Section 4: Hazard Analysis

Transcription

SOUTHSIDE HAMPTON ROADS HAZARD MITIGATION PLAN
HAZARD IDENTIFICATION AND ANALYSIS
INTRODUCTION
This section of the Plan describes the natural hazards that can occur in the Southside Hampton Roads
region and provides information such as general background information, local data (such as the location
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and spatial extent) and historical occurences for each hazard. This section also presents best available
2
data regarding notable historical damages within the region. The hazards discussed in this section are
as follows:
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FLOOD
HURRICANES AND TROPICAL STORMS
SEVERE THUNDERSTORMS
LIGHTNING
TORNADOES
WINTER STORMS AND NOR‟EASTERS
EROSION (COASTAL AND RIVERINE)
EARTHQUAKES
LANDSLIDES
SINKHOLES
DROUGHT
WILDFIRE
DAM/LEVEE FAILURE
TSUNAMIS
EXTREME TEMPERATURES
44 CFR Requirement
Part 201.6(c)(2)(i): The risk assessment shall include a description of the type, location and
extent of all natural hazards that can affect the jurisdiction. The plan shall include information on
previous occurrences of hazard events and on the probability of future hazard events.
Some of these hazards are interrelated (for example, hurricane events can cause flooding and tornado
activity and nor-easters can cause flooding, coastal erosion and winter storm conditions), and thus
discussion of these hazards may overlap where necessary throughout the risk assessment.
To a large extent, historical records are used to identify the level of risk within the planning area—with the
methodological assumption that the data sources cited are reliable and accurate. This section also
provides a series of maps that illustrate the location and spatial extent for those hazards within the region
that have a recognizable geographic boundary (i.e., hazards that are known to occur in particular areas of
1
Significant historical events are based on information made available through the National Oceanic and
Atmospheric Administration (NOAA) unless otherwise cited. In most cases, NOAA information is obtained directly
from NOAA‟s National Climatic Data Center (NCDC), the world‟s largest archive of weather data.
2
Historical damage information is based on best available data and should only be considered approximate figures
for general analysis and planning purposes. More information on the calculation of estimated property damages is
provided in Section 6: Vulnerability Assessment.
4:2
the region such as the 100-year floodplain). For those hazards with potential risk not confined to a
particular geographic area (such as winter storms, thunderstorms and tornadoes), historical event
locations and/or general information on the applicable intensity of these events across the entire planning
area is provided.
It is important to note that for most hazards analyzed in this section, some level of property damage was
possible during any or all of the hazard events cataloged. However, for events that occurred deeper in
the region‟s past, historical records in some instances may show no report of property damage.
Therefore, totals of past property damages derived from historical records are considered to be estimates
and should not be used as a stand-alone indicator of hazard risk.
The next section included in this Plan, the Vulnerability Assessment, further expands upon the foundation
established in this section and provides information on the vulnerability of the jurisdiction in the region to
the hazards presented here.
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SUMMARY OF PRESIDENTIAL DISASTER DECLARATIONS
A presidential disaster declaration is issued when a disaster event has been determined to be beyond the
capabilities of state and local governments to respond. Since 1953— the first year presidential disaster
declarations were issued in the United States—the region has been named in seven such declarations
(Table 4.1). Under a presidential disaster declaration, the state and affected local governments are
eligible to apply for federal funding to pay 75 percent of the approved costs for debris removal,
emergency services related to the storm, and the repair or replacement of damaged public facilities. The
types of natural hazards that led to these disaster declarations in the Southside Hampton Roads region
are ice storms, winter storms and hurricanes.
The most recent disaster to impact the region was Hurricane Isabel which made landfall on September
18, 2003. Hurricane Isabel set records for number of disaster victims, breadth of power outages, dollars
spent for citizen and local government response and recovery, and the largest grant for mitigation
projects for the State. Altogether 100 Commonwealth jurisdictions were declared disaster areas; 93,139
individuals in the declared jurisdictions applied for federal and state assistance; more than $257 million in
state and federal assistance has been provided to individuals and business owners for recovering from
the storm; $105 million was distributed to local governments for debris removal, emergency protective
services and permanent work; and $25,937,544 was provided to support emergency needs such as
water, ice, and generators at critical public facilities.
The second most recent disaster to impact the region occurred during the night of the 24th and lasted
through the 25th of January 2000, when a winter storm produced record breaking snowfall in many areas
of the state. A freezing rain storm on Super Bowl Sunday swept through Virginia and coated much of the
State in heavy ice. As a result, power lines were down and 285,000 Dominion Virginia Power customers
in central Virginia lost power for over three days. The President declared 103 Virginia jurisdictions eligible
for federal disaster assistance on February 28th.
TABLE 4.1: PRESIDENTIAL DISASTER DECLARATIONS ISSUED FOR THE SOUTHSIDE
HAMPTON ROADS REGION
YEAR
DATE
DISASTER
NUMBER
DISASTER TYPE
1972
September 8
339
Tropical Storm Agnes
1996
February 16
1086
Blizzard of 1996
1996
October 23
1135
Hurricane Fran
1998
October 9
1242
Hurricane Bonnie
1999
September 24
1293
Hurricane Floyd
2000
February 28
1318
Severe Winter Storm
2003
September 18
1491
Hurricane Isabel
CITY/COUNTY
Isle of Wight County, Norfolk, Portsmouth,
Suffolk, and Virginia Beach
Suffolk and Virginia Beach
Isle of Wight County and Suffolk
Norfolk, Portsmouth, Suffolk and Virginia
Beach
Suffolk, and Virginia Beach
Isle of Wight County and Suffolk
Suffolk and Virginia Beach
Source: FEMA
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NATIONAL CLIMATIC DATA CENTER STORM EVENT DATABASE
Much of the data on the remaining tables in this section was taken from the National Oceanic and
Atmospheric Administration‟s (NOAA), National Climatic Data Center (NCDC) database. NCDC receives
storm data from the National Weather Service who, in turn, receives their information from a variety of
sources, including, but not limited to: county, state and federal emergency management officials, local law
enforcement officials, skywarn spotters, National Weather Service damage surveys, newspaper clipping
services, the insurance industry and the general public. Information on hazard events not recorded in this
database is discussed in narrative format in each of the following hazard subsections. Because NCDC
data is most accurate beginning from the early to mid 1990‟s it is only marginally useful. In most cases,
local or anecdotal data was used to help supplement the NCDC data to provide a more accurate
depiction of previous hazard occurrences in the region.
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FLOOD
BACKGROUND
Flooding is the most frequent and costly of all natural
hazards in the United States, and has caused more
than 10,000 deaths since 1900. Approximately 90
percent of presidentially declared disasters result
from flood-related natural hazard events. Taken as a
whole, more frequent, localized flooding problems
that do not meet federal disaster declaration
thresholds ultimately cause the majority of damages
across the United States.
Floods are generally the result of excessive
precipitation, and can be characterized as follows:
general floods, in which precipitation occurs over a
given river basin for a long period of time; and flash
Flooding from Hurricane Floyd in Suffolk washes
floods, which are the product of heavy localized
out a road and bridge. Photo courtesy of the City of
precipitation falling in a short time period over a
Suffolk.
given location. The severity of a flood event is
determined by the following factors: a combination of stream and river basin topography and
physiography, hydrology, precipitation and weather patterns, recent soil moisture conditions, and the
degree of vegetative clearing in and around flood-prone areas.
General floods may last for several days or even weeks. The primary types of general flooding include
riverine, coastal and urban flooding. Riverine flooding is a function of excessive precipitation levels and
water runoff volumes within a stream or river. Coastal flooding is typically a result of storm surge, winddriven waves, and heavy rainfall produced by hurricanes, tropical storms, nor‟easters and other large
coastal storms. Urban flooding occurs where man-made development has obstructed the natural flow of
water and decreased the ability of natural groundcover to absorb and retain surface water runoff.
Most flash flooding is caused by slow-moving thunderstorms in a localized area or by heavy rains
associated with hurricanes and tropical storms. Flash flooding can also occur due to accelerated snow
melt, a dam or levee failure, or from a sudden release of water held by an ice jam. Although flash
flooding occurs often along mountain streams, it is also common in urbanized areas where much of the
ground is covered by impervious surfaces. Flash flood waters can move at very high speeds and “walls”
of water have been known to reach heights of 10 to 20 feet. Flash flood waters and the accompanying
debris can uproot trees, roll boulders, destroy buildings, and obliterate bridges and roads.
The periodic flooding of lands including and adjacent to rivers, streams, and shorelines, referred to as the
floodplain, is a natural and inevitable occurrence that can be expected to take place based upon
established recurrence intervals. The recurrence interval of a flood is defined as the average time
interval, in years, expected between a flood event of a particular magnitude and an equal or larger flood.
As the magnitude of a hypothetical flood scenario increases the recurrence interval increases. That is,
the greater the magnitude of a given event, the less likely it will occur over time.
Floodplains are delineated by the frequency of the flood that is large enough to cover them. For example,
the 10-year floodplain will be covered by a 10-year flood (should it occur) and the 100-year floodplain by
the 100-year flood. Flood frequencies such as the 100-year flood are determined by plotting a graph of
the size of all known floods for an area and determining how often floods of a particular size occur.
Another way of expressing the flood frequency is the chance of occurrence (expressed as a percent) in a
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given year of a flood event of a given magnitude. For example, the 100-year flood has a 1 percent
chance of occurring in any given year. Table 4.2 shows flood damage values by fiscal year from a
national perspective.
TABLE 4.2: NATIONAL FLOOD DAMAGE BY FISCAL YEAR (OCTOBER–SEPTEMBER)
FISCAL
YEAR
DAMAGE
1960
$111,168,000
1961
$147,680,000
1962
$86,574,000
1963
$179,496,000
1964
$194,512,000
1965
$1,221,903,000
1966
$116,645,000
1967
$291,823,000
1968
$443,251,000
1969
$889,135,000
1970
$173,803,000
1971
$323,427,000
1972
$4,442,992,000
1973
$1,805,284,000
1974
$692,832,000
1975
$1,348,834,000
1976
$1,054,790,000
1977
$988,350,000
1978
$1,028,970,000
1979
$3,626,030,000
1980
No data
1981
No data
1982
No data
1983
$3,693,572,000
1984
$3,540,770,000
1985
$379,303,000
1986
$5,939,994,000
1987
$1,442,349,000
1988
$214,297,000
1989
$1,080,814,000
1990
$1,636,366,000
1991
$1,698,765,000
1992
$672,635,000
1993
$16,364,710,000
1994
$1,120,149,000
1995
$5,110,714,000
1996
$6,121,753,000
1997
$8,934,923,000
1998
$2,465,048,000
1999
$5,450,375,000
2000
$1,336,744,000
2001
$7,158,700,000
Source: National Weather Service
IMPLICIT PRICE
DEFLATOR
DAMAGE IN
1995 DOLLARS
0.22620
0.22875
0.23180
0.23445
0.23792
0.24241
0.24934
0.25698
0.26809
0.28124
0.29623
0.31111
0.32436
0.34251
0.37329
0.40805
0.43119
0.45892
0.49164
0.53262
0.58145
0.63578
0.67533
0.70214
0.72824
0.75117
0.76769
0.79083
0.81764
0.84883
0.88186
0.91397
0.93619
0.95872
0.97870
1.00000
1.01937
1.03925
1.05199
1.06718
1.08960
1.11539
$491,000,000
$646,000,000
$373,000,000
$766,000,000
$818,000,000
$5,041,000,000
$468,000,000
$1,136,000,000
$1,653,000,000
$3,161,000,000
$587,000,000
$1,040,000,000
$13,698,000,000
$5,271,000,000
$1,856,000,000
$3,306,000,000
$2,446,000,000
$2,154,000,000
$2,093,000,000
$6,808,000,000
No data
No data
No data
$5,260,000,000
$4,862,000,000
$505,000,000
$7,737,000,000
$1,824,000,000
$262,000,000
$1,273,000,000
$1,856,000,000
$1,859,000,000
$718,000,000
$17,069,000,000
$1,145,000,000
$5,111,000,000
$6,005,000,000
$8,597,000,000
$2,343,000,000
$5107,000,000
$1227,000,000
$6418,000,000
U.S. POPULATION
(MILLIONS)
180.671
183.691
186.538
189.242
191.889
194.303
196.560
198.712
200.706
202.677
205.052
207.661
209.896
211.909
213.854
215.973
218.035
220.239
222.585
225.055
227.225
229.466
231.664
233.792
235.825
237.924
240.133
242.289
244.499
246.819
249.464
252.153
255.030
257.783
260.327
262.803
265.229
267.784
270.248
272.691
282.125
284.797
DAMAGE PER
CAPITA
(1995 DOLLARS)
2.72
3.51
2.00
4.05
4.26
25.94
2.38
5.71
8.24
15.60
2.86
5.01
65.26
24.87
8.68
15.31
11.22
9.78
9.40
30.25
0.00
0.00
0.00
22.50
20.62
2.12
32.22
7.53
1.07
5.16
7.44
7.37
2.82
66.22
4.40
19.45
22.64
32.11
8.67
18.73
4.35
22.54
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LOCATION AND SPATIAL EXTENT
Hydrological features are plentiful in the Southside Hampton Roads region. From the Chesapeake Bay,
to the Elizabeth River and branches, the Blackwater River in Isle of Wight County and the Atlantic Ocean
along the shores of Virginia Beach, water is a major part of the way of life in the region. When heavy or
prolonged rainfall events and/or hurricanes, tropical storms and other coastal storms (including
nor‟easters) occur, these rivers, streams and bodies of water are susceptible to some degree of riverine
and coastal flooding. There have been a number of past riverine and coastal flooding events, ranging
widely in terms of location, magnitude and impact. Other flood events that occur in the region are
localized in nature, resulting from heavy rains occurring in a short period of time over urbanized areas
that are not able to adequately handle stormwater runoff. These events typically do not threaten lives or
3
property and do not result in emergency or disaster declarations.
The coastal flooding hazards associated with hurricanes and tropical storms are included separately
under the “flood” hazard. In so doing, the storm surge hazard has been identified as a unique flood and
will be addressed separately from the “100-year” coastal and riverine flood hazard in the Hazard
Identification and Analysis and Vulnerability Assessment sections.
Figures 4.1 through 4.7 show the existing potential flood hazard areas throughout the region based on
the best available GIS data for FEMA‟s identified 100-year floodplains (areas inundated by a flood with a
recurrence interval of once every hundred years, also referred to as the flood with an annual chance of
one percent). The official flood maps for each jurisdiction in the region vary in age. Where available,
more detailed flood hazard data for each participating jurisdiction within the region is provided in Section
5: Vulnerability Assessment.
Figures 4.8 through 4.12 show the storm surge hazard areas that can be expected as the result of
Category 2, 3 and 4 hurricanes, based on the Sea, Lake and Overland Surge from Hurricanes (SLOSH)
model. SLOSH is a computerized model run by the National Weather Service to estimate storm surge
heights resulting from hypothetical hurricanes by taking into account the maximum of maximums of
various category hurricanes as it relates to pressure, size, forward speed and sustained winds. The
regional analysis represents the composite maximum water inundation levels for a series of parallel tracks
making landfall at various points along the coast. The SLOSH model, therefore, is best used for defining
the “worst case scenario” of potential maximum surge for particular locations as opposed to the regional
impact of one singular storm surge event.
3
The vast majority of flood events in the United States do not meet the per capita damage thresholds required to
trigger a presidential disaster declaration and the release of large sums of federal aid. This fact demonstrates the
need for local governments to establish a comprehensive mitigation strategy that includes achievable actions that do
not rely entirely on assistance from the state and federal government.
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SIGNIFICANT HISTORICAL EVENTS4
Many of the historical flood events that have
occurred in the region have been the result of
coastal storms, tropical storms or hurricanes. Other
localized flooding occurs when heavy rains fall
during high tide causing waters that would normally
drain quickly to back up because of the tides. Based
on historical and anecdotal evidence, it is clear that
there is a relatively high frequency of flooding in the
region. Some of the notable flood events to impact
the region are discussed below.
The Storm of 1749 is one of the most notable
storms to occur in this region. It was responsible for
the formation of Willoughby Spit, a formation of land
approximately two miles long and a quarter mile
wide. This storm created a fifteen (15) foot storm
surge that flooded much of the region.
Photo credit: City of Portsmouth.
An unnamed hurricane struck the region on August 23, 1933 and created a high tide in Norfolk of 9.69
feet above Mean Lower Low Water (MLLW), a record for the area. Eighteen people were killed by this
storm that also flooded downtown Norfolk and destroyed homes at Ocean View. Winds were recorded at
70 mph in Norfolk, 82 mph at Cape Henry, and 88 mph at the Naval Air Station in Norfolk.
The Ash Wednesday storm of 1962 produced very high flooding throughout the Southside Hampton
Roads region partly because it occurred during "Spring Tide" (sun and moon phase to produce a higher
than normal tide). The storm moved north off the coast past Virginia Beach and then reversed its course
moving again to the south and bringing with it higher tides and higher waves which battered the coast for
several days. The storm's center was 500 miles off the Virginia Capes when water reached 9 feet at
Norfolk and 7 feet on the coast. Huge waves toppled houses into the ocean and broke through Virginia
Beach's concrete boardwalk and sea wall. Houses on the bay side also saw extensive tidal flooding and
wave damage. The beaches and shorefront had severe erosion. Locals indicated that the damage from
this storm was worse in Virginia Beach than that caused by the 1933 Hurricane. The islands of
Chincoteague and Assateague were completely submerged. Receding water exposed hundreds of
thousands of dead chickens drowned by the flooding. The Virginia Department of Health indicated that it
was an extreme health hazard and asked all women, children and elderly to evacuate. A million dollars in
damage was done to NASA's Wallops Island launch facility and an estimated $4 million in wind and flood
damages occurred to the City of Hampton. Winds were recorded at speeds up to 70 mph causing 40-foot
waves at sea. This storm also produced Virginia's greatest 24-hour snowfall with 33 inches and the
greatest single storm snowfall with 42 inches (these were recorded to the West in the Shenandoah
Mountains).
4
Many of the flood events that have occurred in the Southside Hampton Roads Region have been caused by
hurricanes, tropical storms or nor‟easters that have impacted the region. Therefore, there will be some duplication of
discussions about the significant historical events across the different hazards.
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In September of 1999, Hurricane Floyd was
responsible for wind and flood damage in the Southside
Hampton Roads region. Several trees were uprooted
as wind speeds were recorded between 50 and 80 mph
across the region. Flood waters washed out parts of
Route 10 between Isle of Wight County and Suffolk.
Highway 32, a major evacuation route, was flooded in
Suffolk. Suffolk reported 78 homes and 25 businesses
damaged by floodwaters and many other homes and
businesses were flooded across the region.
In September of 2003, Hurricane Isabel caused
flooding in the region that in some areas was as bad as
the flooding caused by the 1933 hurricane and the Ash
Wednesday Storm of 1962.
Table 4.3 provides information on 21 significant flood
events that are known to have occurred between 1994
Rainfall totals from Hurricane Floyd.
and 2004 in the Southside Hampton Roads region.
Source: NOAA Climate Prediction Center
The flood events documented by the National Climatic
Data Center resulted in a total within the region of no known deaths or injuries, and only approximately
5
$670,000 in total reported property damages.
TABLE 4.3: SIGNIFICANT FLOOD EVENTS (1993-2004)
LOCATION
Norfolk,
Virginia
Beach,
Hampton
Roads, and
Isle of
Wight
County
DATE OF
OCCURRENCE
TYPE OF
EVENT
DEATHS/
INJURIES
PROPERTY
DAMAGE
11/17/1994
Coastal
Flooding
0/ 0
$605,000
DETAILS
Strong easterly flow between Hurricane
Gordon, a category 1 storm meandering
150 miles south of Cape Hatteras, and a
strong anticyclone over New England,
caused significant coastal flooding and
damage in the Sandbridge section of
Virginia Beach, beginning around noon on
November 17th. The worst flooding
occurred on the 18th when tides were
running up to 4 feet above normal. The
heaviest damage occurred along 14th
street, where 100 feet of the fishing pier
washed away. Several homes suffered
minor damage, with two requiring extra
work to remain in place. A 1000-foot
stretch of road and several protective steel
bulkheads were damaged. The abovenormal tides caused other minor flooding
in Tidewater. The Nansemond River
overflowed its banks in Suffolk and caused
minor flooding. High tides on the James
and Pagan Rivers caused several roads to
be under water in eastern Isle of Wight
County.
5
Obviously, there has been more monetary flood damage in the region other than that recorded by the National
Climatic Data Center.
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4:10
DATE OF
OCCURRENCE
TYPE OF
EVENT
DEATHS/
INJURIES
PROPERTY
DAMAGE
Norfolk,
Virginia
Beach,
Suffolk, and
Isle of
Wight
County
12/23/1994
Coastal
Flooding
0/ 0
$65,000
Norfolk
7/18/1996
Flash Flood
0/ 0
$0
Virginia
Beach
7/18/1996
Flash Flood
0/ 0
0
Portsmouth
7/24/1999
Flash Flood
0/ 0
$0
Suffolk
Norfolk
7/24/1999
7/24/1999
Flash Flood
Flash Flood
0/ 0
0/ 0
$0
$0
Virginia
Beach
Portsmouth
Norfolk
7/24/1999
Flash Flood
0/ 0
0
8/14/1999
8/14/1999
Flash Flood
Flash Flood
0/ 0
0/ 0
$0
$0
Virginia
Beach
Portsmouth
Suffolk
8/14/1999
Flash Flood
0/ 0
0
9/7/1999
9/7/1999
Flash Flood
Flash Flood
0/ 0
0/ 0
$0
$0
Norfolk
Virginia
Beach
9/7/1999
9/7/1999
Flash Flood
Flash Flood
0/ 0
0/ 0
$0
0
LOCATION
DETAILS
A double-structured storm system
produced minor coastal flooding in the
Tidewater region. The effects were much
less than expected as the main storm
moved well east of the mid-Atlantic before
curling northwest into Long Island. In the
Sandbridge section of Virginia Beach, a
beachfront home collapsed into the sea.
The combination of pounding surf and
wind from Hurricane Gordon in late
November and this event finished off the
home. In addition, a few more bulkheads
were flattened. Several roads in the
Tidewater area suffered minor flooding,
including Rescue Road in the Town of
Smithfield.
One to two inches of rain within six hours
produced flooding along the 300-400 block
of East Little Creek Road. Also, people
were trapped in cars with water waist high
along Campostella Road.
Two to four inches of rain within six hours
produced flooding in the Kempsville area
along Indian River Road and Princess
Anne Road. Also, high water was reported
in the Oceanfront area along Atlantic
Avenue.
Parts of Interstate 264 were covered with
more than 3 feet of water. Some other
roads were impassable. Spotter reported
just over 7 inches of rain in 4 hours.
Many roads were flooded and impassable.
Many roads including Hampton Boulevard
were flooded and impassable.
Many roads were flooded and impassable.
Numerous underpasses flooded.
Numerous primary roads flooded. Many
underpasses flooded.
Numerous primary roads and underpasses
flooded.
No details available
1500 block of Camp Pond Road flooded
out.
No details available
A slow-moving line of thunderstorms with
very heavy rains caused numerous
flooded roads throughout the area, with
some secondary roads impassable.
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4:11
DATE OF
OCCURRENCE
TYPE OF
EVENT
DEATHS/
INJURIES
PROPERTY
DAMAGE
Virginia
Beach,
Hampton
Roads,
Portsmouth
and Isle of
Wight
County
9/15/1999
Flood
0/ 0
$0
Suffolk
9/15/1999
Flood
0/ 0
$0
LOCATION
DETAILS
Very heavy rain from Hurricane Floyd
produced widespread flooding and flash
flooding across much of central and
eastern Virginia, and northeast North
Carolina. Rainfall amounts generally
ranged from 12 to 18 inches in much of
the region. Numerous roads were washed
out due to flooding. Many areas normally
prone only to flooding of poor drainage
and low lying areas experienced
significant flash flooding. Also, there were
enormous agricultural/crop losses due to
the flooding.
ranged from 12 to 18 inches in much of
the Virginia Tidewater. Numerous roads
were washed out due to flooding. Many
areas normally prone only to flooding of
poor drainage and low lying areas
experienced significant flash flooding.
River flooding was extensive and
prolonged in the Chowan River Basin. The
Blackwater, Meherrin and Nottoway Rivers
exceeded flood stage. Also, there were
enormous agricultural/crop losses due to
the flooding.
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4:12
DATE OF
OCCURRENCE
TYPE OF
EVENT
DEATHS/
INJURIES
PROPERTY
DAMAGE
Norfolk
9/15/1999
Flood
0/ 0
$0
Isle of
Wight
Countywide
10/17/1999
Flash Flood
0/ 0
$0
Portsmouth
10/17/1999
Flash Flood
0/ 0
$0
Suffolk
10/17/1999
Flash Flood
0/ 0
$0
Norfolk
10/17/1999
Flash Flood
0/ 0
$0
Virginia
Beach
10/17/1999
Flash Flood
0/ 0
0
Norfolk
7/26/2000
Flash Flood
0/ 0
$0
Suffolk
7/30/2000
Flash Flood
0/ 0
$0
LOCATION
DETAILS
ranged from near 7 inches from eastern
Caroline County to Richmond City to
Brunswick, Lunenburg and Mecklenburg
counties, to 12 to 18 inches in much of the
region. Numerous roads were washed out
due to flooding. Many areas normally
prone only to flooding of poor drainage
and low lying areas experienced
significant flash flooding. Primary routes
out of service included US 460 near
Wakefield, US 58 near Emporia and
Franklin, and Interstate 95 south of
Petersburg to Emporia. River flooding was
extensive and prolonged in the Chowan
River Basin. The Blackwater, Meherrin
and Nottoway Rivers exceeded flood
stage. Water levels in the city of Franklin
were estimated to be several feet above
the flood of record which occurred in
August 1940. The flooding was considered
to be a 500 year flood of record. Also,
there were enormous agricultural/crop
losses due to the flooding.
Very heavy rainfall, locally up to 5 to 9
inches, associated with Hurricane Irene,
resulted in numerous flooded roads and
roads closed due to high water.
inches, associated with Hurricane Irene
Heavy rain flooded roadways and caused
closure of underpasses on Tidewater
Drive in downtown Norfolk. Flooding also
occurred at Chesapeake Boulevard and
Chesapeake Street in the East Ocean
View section of Norfolk.
Heavy rain caused flooding of Kings Fork
Road in the western part of the city.
MAY 2006
4:13
LOCATION
DATE OF
OCCURRENCE
TYPE OF
EVENT
DEATHS/
INJURIES
PROPERTY
DAMAGE
Portsmouth
8/11/2000
Flash Flood
0/ 0
$0
Norfolk
8/11/2000
Flash Flood
0/ 0
$0
Virginia
Beach
8/14/2000
Flash Flood
0/ 0
0
Norfolk
9/5/2000
Flash Flood
0/ 0
$0
Windsor
6/16/2001
Flash Flood
0/ 0
$0
Suffolk
6/16/2001
Flash Flood
0/ 0
$0
Norfolk
7/23/2001
Flash Flood
0/ 0
$0
Norfolk
8/28/2002
Flash Flood
0/ 0
$0
Virginia
Beach
8/28/2002
Flash Flood
0/ 0
0
Norfolk
10/11/2002
Flash Flood
0/ 0
$0
DETAILS
Very heavy rain caused flooding and the
closure of Interstate 264 at Frederick
Boulevard.
Extremely heavy rain caused widespread
flooding of roads in downtown Norfolk. The
intersections of Granby Street and
Brambleton Avenue, Princess Anne Road
and Monticello Avenue, and City Hall
Avenue and Granby Street were all closed
due to high standing water. Also,
underpasses on Campostella Avenue,
Tidewater Drive and Colley Avenue in
Norfolk were closed due to accumulated
water. In Portsmouth, Interstate 264 at
Frederick Boulevard was closed due to
standing water.
Very heavy rain caused widespread
flooding and closure of roads in the vicinity
of Princess Anne Plaza. Also, sections of
Rosemont Road were closed due to
flooding.
Heavy rain from slow-moving
thunderstorms caused the side of an
underpass wall to slide into the road at
Granby Street and Interstate 64 resulting
in road closure.
Knoxville Road, Rose Drive, and
numerous other secondary roads
impassable around Windsor.
Flooding reported near Whaleyville. One
street closed.
Car submerged at the underpass on
Colley Avenue and 21st Street. Also,
numerous roads covered by 1 to 2 feet of
water.
Rainfall amounts of 2 to 3 inches within 2
hours caused roads to be closed or
blocked due to high water. Union Street
and areas near City Hall and Granby were
flooded. Cars were reported stalled out in
deep water, also.
Rainfall amounts of 2 to 3 inches within 2
hours caused some roads to be closed or
blocked due to high water. Rosemont at
the Virginia Beach Boulevard and around
the Kings Grant area were closed or
blocked. Cars were reported stalled out in
deep water, also.
Rainfall amounts between 3 and 3.5
inches caused flooding of some streets
and low lying intersections, including the
intersection of Tidewater Drive and
Virginia Beach Boulevard.
MAY 2006
4:14
DATE OF
OCCURRENCE
TYPE OF
EVENT
DEATHS/
INJURIES
PROPERTY
DAMAGE
10/11/2002
Flash Flood
0/ 0
0
Portsmouth
Suffolk
Airport
9/3/2003
9/3/2003
Flash Flood
Flash Flood
0/ 0
0/ 0
$0
$0
Norfolk
9/3/2003
Flash Flood
0/ 0
$0
Portsmouth
6/10/2004
Flash Flood
0/ 0
$0
Isle of
Wight
7/25/2004
Flash Flood
0/ 0
$0
Norfolk
7/25/2004
Flash Flood
0/ 0
$0
Portsmouth
8/2/2004
Flash Flood
0/ 0
$0
Norfolk
8/2/2004
Flash Flood
0/ 0
$0
0/0
$670,000
LOCATION
Virginia
Beach
TOTAL
DETAILS
Rainfall amounts between 3 and 3.5
inches caused flooding and closure of
Atlantic Avenue between 42nd and 65th
streets.
Waist high water reported on some roads.
Flooding of streets in northern Suffolk.
Water as high as mailboxes in a cul-desac.
Many roads closed due to high water,
including 8000 block of Hampton
Boulevard.
Six inches of water across road at Airline
Boulevard and I264. One foot of water
across road at intersection of Oregon and
Dakota Roads.
Lawnes Creek Bridge on Route 10 near
Rushmere reported closed due to flooding.
Also, several other roads were closed due
to flooding in the northern part of the
county.
Many streets flooded in downtown Norfolk
including Waterside Drive.
Duke and Randolph Streets reported
closed due to high water. Flooding on I264 and Portsmouth Boulevard.
Flooding reported at the intersection of
Park Avenue and Virginia Beach
Boulevard, and at the intersection of
Robinhood Road and I-64 underpass.
Source: National Climatic Data Center (1993 to 2004 data)
PROBABILITY OF FUTURE OCCURRENCES
Flooding remains a highly likely occurrence throughout the identified flood hazard areas of the region.
Smaller floods caused by heavy rains and inadequate drainage capacity will be more frequent, but not as
costly as the large-scale floods which may occur at less frequent intervals, including extended torrential
rainfall and storm surge events associated with hurricanes, tropical storms and nor‟easters. While the
potential for flood is always present, many of the jurisdictions within the region do have policies in place
6
that should help lessen potential property damage due to future floods.
6
The Capability Assessment section of this Plan provides an overview of the programs and policies that each
jurisdiction has in place that are designed to reduce the impacts of the flood hazard.
MAY 2006
4:15
HURRICANES AND TROPICAL STORMS
BACKGROUND
Hurricanes and tropical storms, along with nor‟easters and
typhoons, are classified as cyclones and are any closed
circulation developing around a low-pressure center in which
the winds rotate counter-clockwise in the Northern
Hemisphere (or clockwise in the Southern Hemisphere) and
whose diameter averages 10 to 30 miles across. A tropical
cyclone refers to any such circulation that develops over
tropical waters. Tropical cyclones act as a “safety-valve,”
limiting the continued build-up of heat and energy in tropical
regions by maintaining the atmospheric heat and moisture
balance between the tropics and the pole-ward latitudes.
The primary damaging forces associated with these storms
are high-level sustained winds, heavy precipitation, and
tornadoes. Coastal areas are particularly vulnerable to
storm surge, wind-driven waves, and tidal flooding which can
7
prove more destructive than cyclone wind .
The key energy source for a tropical cyclone is the release of
latent heat from the condensation of warm water. Their
Hurricane Isabel approaches North
formation requires a low-pressure disturbance, warm sea
Carolina and Virginia in September of
surface temperature, rotational force from the spinning of the
2003. (Photo courtesy of NASA)
earth, and the absence of wind shear in the lowest 50,000
feet of the atmosphere. The majority of hurricanes and
tropical storms form in the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico during the official Atlantic
hurricane season, which encompasses the months of June through November. The peak of the Atlantic
hurricane season is in early to mid-September. Based on a long-term average, approximately six storms
reach hurricane intensity per year.
Figure 4.13 shows, for any particular location, the chance of a hurricane or tropical storm affecting the
area sometime during the Atlantic hurricane season. The figure was created by the National Oceanic and
Atmospheric Administration‟s (NOAA) Hurricane Research Division, using data from 1944 to 1999. The
figure shows the number of times a storm or hurricane was located within approximately 100 miles (165
kilometers) of a given spot in the Atlantic basin.
7
For purposes of this risk assessment, coastal flood hazards associated with hurricanes and tropical storm events
are included separately under the “flood” hazard.
MAY 2006
4:16
FIGURE 4.13: EMPIRICAL PROBABILITY OF A NAMED HURRICANE OR TROPICAL STORM
Source: National Oceanic and Atmospheric Administration, Hurricane Research Division
As an incipient hurricane develops, barometric pressure (measured in millibars or inches) at its center
falls and winds increase. If the atmospheric and oceanic conditions are favorable, it can intensify into a
tropical depression. When maximum sustained winds reach or exceed 39 miles per hour, the system is
designated a tropical storm, given a name, and is monitored by the National Hurricane Center in Miami,
Florida. When sustained winds reach or exceed 74 miles per hour the storm is deemed a hurricane.
Hurricane intensity is further classified by the Saffir-Simpson Scale which rates hurricane intensity on a
scale of 1 to 5, with 5 being the most intense. The Saffir-Simpson Scale is shown in Table 4.4.
TABLE 4.4: SAFFIR-SIMPSON SCALE
CATEGORY
MAXIMUM SUSTAINED WIND SPEED (MPH)
1
2
3
4
5
74–95
96–110
111–130
131–155
155 +
MINIMUM SURFACE
STORM SURGE
PRESSURE (MILLIBARS)
(FEET)
Greater than 980
979–965
964–945
944–920
Less than 920
3–5
6–8
9–12
13–18
19+
Source: Federal National Hurricane Center
MAY 2006
4:17
The Saffir-Simpson Scale categorizes hurricane intensity linearly based upon maximum sustained winds,
barometric pressure, and storm surge potential, which are combined to estimate potential damage.
Categories 3, 4, and 5 are classified as “major” hurricanes, and while hurricanes within this range
comprise only 20 percent of total tropical cyclones making landfall, they account for over 70 percent of the
damage in the United States. Table 4.5 describes the damage that could be expected for each hurricane
category.
TABLE 4.5: HURRICANE DAMAGE CLASSIFICATIONS
STORM
DAMAGE LEVEL
CATEGORY
DESCRIPTION OF DAMAGES
No real damage to building structures. Damage primarily
to unanchored mobile homes, shrubbery, and trees. Also,
some coastal flooding and minor pier damage.
1
MINIMAL
2
MODERATE
Some roofing material, door, and window damage.
Considerable damage to vegetation, mobile homes, etc.
Flooding damages piers and small craft in unprotected
moorings may break their moorings.
3
EXTENSIVE
Some structural damage to small residences and utility
buildings, with a minor amount of curtainwall failures.
Mobile homes are destroyed. Flooding near the coast
destroys smaller structures, with larger structures damaged
by floating debris. Terrain may be flooded well inland.
4
EXTREME
More extensive curtainwall failures with some complete
roof structure failure on small residences. Major erosion of
beach areas. Terrain may be flooded well inland.
5
PHOTO EXAMPLE
Complete roof failure on many residences and industrial
buildings. Some complete building failures with small utility
CATASTROPHIC buildings blown over or away. Flooding causes major
damage to lower floors of all structures near the shoreline.
Massive evacuation of residential areas may be required.
Sources: National Hurricane Center and the Federal Emergency Management Agency
A storm surge is a large dome of water often 50 to 100 miles wide and rising anywhere from four to five
feet in a Category 1 hurricane up to 20 feet in a Category 5 storm. The storm surge arrives ahead of the
storm‟s actual landfall and the more intense the hurricane is, the sooner the surge arrives. Water rise can
be very rapid, posing a serious threat to those who have not yet evacuated flood-prone areas. A storm
surge is a wave that has outrun its generating source and become a long period swell. The surge is
always highest in the right-front quadrant of the direction in which the hurricane is moving. As the storm
approaches shore, the greatest storm surge will be to the north of the hurricane eye. Such a surge of
high water topped by waves driven by hurricane force winds can be devastating to coastal regions,
causing severe beach erosion and property damage along the immediate coast.
Storm surge heights and associated waves are dependent upon the shape of the continental shelf
(narrow or wide) and the depth of the ocean bottom (bathymetry). A narrow shelf, or one that drops
MAY 2006
4:18
steeply from the shoreline and subsequently produces deep water close to the shoreline, tends to
produce a lower surge but higher and more powerful storm waves.
Damage during hurricanes may also result from spawned tornadoes and inland flooding associated with
heavy rainfall that usually accompanies these storms. Hurricane Floyd, for example, was at one time a
Category 4 hurricane racing towards the North Carolina coast. As far inland as Raleigh, the state capital
located more than 100 miles from the coast, communities were preparing for winds exceeding 100 miles
per hour. While Floyd made landfall as a Category 2 hurricane it caused the worst inland flooding
disaster in North Carolina‟s history. Rainfall amounts exceeded 20 inches in certain locales and 67
counties sustained damages.
Similar to hurricanes, nor‟easters are ocean storms capable of causing substantial damage to coastal
areas in the Eastern United States due to their strong winds and heavy surf. Nor'easters are named for
the winds that blow in from the northeast and drive the storm up the East Coast along the Gulf Stream, a
band of warm water that lies off the Atlantic coast. They are caused by the interaction of the jet stream
with horizontal temperature gradients and generally occur during the fall and winter months when
moisture and cold air are plentiful.
Nor‟easters are known for dumping heavy amounts of rain and snow, producing hurricane-force winds,
and creating high surf that causes severe beach erosion and coastal flooding. There are two main
components to a nor'easter: (1) a Gulf Stream low-pressure system (counter-clockwise winds) generated
off the southeastern U.S. coast, gathering warm air and moisture from the Atlantic, and pulled up the East
Coast by strong northeasterly winds at the leading edge of the storm; and (2) an Arctic high-pressure
system (clockwise winds) which meets the low-pressure system with cold, arctic air blowing down from
Canada. When the two systems collide, the moisture and cold air produce a mix of precipitation and have
the potential for creating dangerously high winds and heavy seas. As the low-pressure system deepens,
the intensity of the winds and waves increase and can cause serious damage to coastal areas as the
8
storm moves northeast.
8
Depending on the location of jurisdictions participating in the Southside Hampton Roads Hazard Mitigation Plan,
nor‟easters are viewed as winter storm or coastal events, as the coastal storm characteristics and coastal impacts of
nor‟easters are limited to coastal communities. The Dolan-Davis Nor‟easter Intensity Scale, which shows levels of
coastal degradation based on beach and dune erosion, overwash and coastal property damage is particularly
relevant to jurisdictions such as Virginia Beach, and to a lesser extent Norfolk, Portsmouth and parts of Isle of Wight
County.
MAY 2006
4:19
Since the mid-1800s, numerous tropical cyclones
have affected Virginia on a statewide basis, causing
the deaths of an estimated 228 people and costing
the Commonwealth more than a billion dollars in
damages. The eyes of over 70 storms have tracked
directly across Virginia with 11 having made landfall
on or within 60 miles of the Virginia Coast. The
region is geographically located in an area that can
expect to experience hurricane damage in any given
year.
In fact, 106 such storms have passed within 75 miles
of the Southside Hampton Roads region since 1851
(Figure 4.14), 29 of which crossed directly through
the region. 2 Category 3 hurricanes passed within
75 miles of the region (both unnamed storms in 1879
and 1899), 14 were Category 2 hurricanes, 31 were
Category 1 hurricanes and 117 were tropical storms.
Of the storms that passed through the region,
Hurricane Ivan was the most recent in 2004.
Remains of a restaurant in Isle of Wight County
after Hurricane Isabel. Photo credit: Isle of Wight
County
Hurricane winds impact each jurisdiction uniformly. All building stock, infrastructure and critical facilities
are equally vulnerable to these hazards. Vulnerability maps showing infrastructure and critical facilities
that are at risk to these hazards are found in Appendix B.
MAY 2006
4:20
SIGNIFICANT HISTORICAL EVENTS9
The National Weather Service began keeping weather records on January 1, 1871. Prior to that,
information on past hurricanes and tropical storms to impact the Southside Hampton Roads region were
taken from ships logs, accounts from local citizens, newspapers and other source. There are several
10
historical references to major storms that affected coastal Virginia in the 1600's and 1700's . Some of
these storms were strong enough to alter land masses, including the widening of the Lynnhaven River
(September 6, 1667) and formation of Willoughby Spit (October 19, 1749). These reports also indicate
severe flooding caused by these storms (12-15 feet of flooding in some cases).
Better records have been kept since 1871. One for the first of the storms to be well documented was a
hurricane that occurred in October 1878 that resulted in Cobb and Smith Islands on the Eastern Shore
being completely submerged.
One of the worst storms to impact the region occurred in August 1933 when a hurricane known as the
Chesapeake-Potomac Hurricane of 1933 passed just west of the Hampton Roads area. The storm
made landfall in northeastern North Carolina and moved northwest. This hurricane produced the record
high tide for the area which exists today, at a level of 9.69 feet above Mean Lower Low Water. The
highest sustained wind was clocked was 88 mph at the Naval Air Station (NAS). Less than a month later,
another hurricane struck the area with winds again clocked at 88 mph at NAS, but tides only rose to 8.3
feet above Mean Lower Low Water.
Another unnamed storm occurred in September of 1944 creating the fastest 1 minute wind speed to ever
be recorded in the area (134 mph at Cape Henry). Gusts were estimated to 150 mph. The local National
Weather Service office recorded 72 mph winds with gusts to 90 mph.
Although the center of circulation for Hurricane Hazel did not pass within 75 miles of the region, wind
speeds of 78 mph were recorded at Norfolk Airport with gusts up to 100 mph and an unofficial reading of
130 mph was also reported in Hampton.
In 1960 Hurricane Donna passed through the region with a fastest 1 minute wind speed of 73 mph at
Norfolk Airport, 80 mph at Cape Henry and estimated 138 mph at Chesapeake Light Ship. Lowest
pressure of 28.65 inches holds the area record for a tropical storm. 3 deaths were documented in
association with this hurricane.
On August 27, 1998, Hurricane Bonnie tracked over the region after passing over the northern Outer
Banks. Winds speeds were sustained at 46 mph with gust to 64 mph at Norfolk Airport. Four to seven
inches of rain combined with near hurricane force winds knocked out power to 320,000 customers across
Virginia. Highest tide was recorded at 6.0 feet above Mean Lower Low Water. This was the most
significant storm to impact the region since 1960 (Hurricane Donna)
On September 6, 1999, Hurricane Floyd passed directly over Virginia Beach on a track similar to
Hurricane Donna in 1960. Wind speeds were recorded at 31 mph with gust to 46 mph. Rainfall amounts
of 12-18" were recorded in portions of eastern Virginia causing extensive flooding in portions of the
Southside Hampton Roads region.
Just as the rest of the country has experienced, Southeastern Virginia has felt the impacts of very active
hurricane seasons for the past ten years. In 1996, Hurricanes Bertha and Fran impacted the region,
followed by Hurricane Danny in 1997, Hurricane Bonnie in 1998, and Hurricanes Dennis, Floyd, and Irene
9
As previously mentioned, many of the significant hurricane, coastal storm and tropical storm events were also
significant flooding events. As such, many of the significant historical events for hurricanes may also be discussed in
the description of the flood hazard.
10
The first historical reference to a major hurricane that could have affected the Virginia coast was in August 24,
1635.
MAY 2006
4:21
in 1999. Although each of these storms were downgraded by the time they reached the Southside
Hampton Roads region, they each created problems for the region when they passed through, two of
which resulted in Federal Disaster declarations (Bonnie and Floyd) for the region. Tropical storms Helene
in 2000 and Kyle occurred in 2002, and most recently, Hurricane Isabel caused major damage in the
region in 2003 (winds speeds of 54 mph with gusts to 75 mph in Norfolk and significant beach erosion
was reported).
Table 4.5 shows the historical storm tracks within 75 miles of Southside Hampton Roads region since
1851 that are the basis for Figure 4.14.
TABLE 4.5: HISTORICAL STORM TRACKS WITHIN 75 MILES OF THE REGION (SINCE 1851)
DATE OF OCCURRENCE
STORM NAME
WIND SPEED
(MPH)
STORM CATEGORY
8/25/1851
9/10/1854
8/20/1856
9/17/1859
9/27/1861
11/2/1861
9/18/1863
10/26/1872
9/29/1874
9/17/1876
10/23/1878
8/18/1879
9/9/1880
9/10/1881
9/11/1882
9/23/1882
9/12/1883
8/26/1885
7/2/1886
9/11/1888
10/12/1888
9/25/1889
6/17/1893
10/23/1893
9/29/1894
10/10/1894
9/23/1897
10/26/1897
8/18/1899
10/31/1899
7/11/1901
6/16/1902
9/15/1904
9/1/1908
8/25/1918
12/3/1925
9/19/1928
8/23/1933
9/16/1933
9/6/1935
9/18/1936
8/2/1944
9/14/1944
10/20/1944
6/26/1945
7/7/1946
8/14/1953
8/31/1954
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
UNNAMED
BARBARA
CAROL
45
45
60
60
70
80
70
45
70
90
105
115
80
70
45
45
45
80
40
40
60
45
65
50
85
75
70
60
120
65
80
40
65
50
40
45
45
80
90
75
100
50
105
40
50
65
105
100
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
CATEGORY 1 HURRICANE
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
MAY 2006
4:22
TABLE 4.5: HISTORICAL STORM TRACKS WITHIN 75 MILES OF THE REGION (SINCE 1851)
DATE OF OCCURRENCE
STORM NAME
WIND SPEED
(MPH)
STORM CATEGORY
8/12/1955
9/20/1955
7/10/1959
7/30/1960
9/12/1960
9/14/1961
9/1/1964
9/17/1967
8/28/1971
6/22/1972
7/1/1981
9/30/1983
9/14/1984
9/27/1985
8/18/1986
9/25/1992
7/13/1996
7/24/1997
8/28/1998
9/16/1999
9/24/2000
10/12/2002
9/18/2003
8/14/2004
CONNIE
IONE
CINDY
BRENDA
DONNA
UNNAMED
CLEO
DORIA
DORIA
AGNES
BRET
DEAN
DIANA
GLORIA
CHARLEY
DANIELLE
BERTHA
DANNY
BONNIE
FLOYD
HELENE
KYLE
ISABEL
CHARLEY
80
70
40
50
105
40
45
40
65
50
60
65
60
105
80
65
75
45
85
80
45
45
100
40
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
TROPICAL STORM
Source: National Hurricane Center
It is likely that the region will be impacted by hurricanes and tropical storms in the future. The region is
less likely to experience the effects of a major (Category 3 or stronger) hurricane, however it remains a
possibility. The effects of smaller hurricanes (Categories 1 and 2 with wind speeds from 74-110 miles per
hour) and tropical storms (sustained wind speeds of at least 39 miles per hour and torrential rains) will be
more frequent, as storms making landfall along the North Carolina and Virginia coastlines could impact
the region in any given year.
MAY 2006
4:23
SEVERE THUNDERSTORMS
BACKGROUND
According to the National Weather Service, more than 100,000 thunderstorms occur each year, though
only about 10 percent of these storms are classified as “severe.” Although thunderstorms generally affect
a small area when they occur, they are very dangerous because of their ability to generate tornadoes,
hailstorms, strong winds, flash flooding, and damaging lightning. While thunderstorms can occur in all
regions of the United States, they are most common in the central and southern states because
atmospheric conditions in those regions are most ideal for generating these powerful storms.
Thunderstorms are caused when air masses of varying temperatures meet. Rapidly rising warm moist air
serves as the “engine” for thunderstorms. These storms can occur singularly, in lines, or in clusters.
They can move through an area very quickly or linger for several hours.
The National Weather Service collected data for thunder days, number and duration of thunder events,
and lightening strike density for the 30-year period from 1948 to 1977. A series of maps was generated
showing the annual average thunder event duration, the annual average number of thunder events, and
the mean annual density of lightning strikes.
Figure 4.15 illustrates thunderstorm hazard severity based on the annual average number of thunder
events from 1948 to 1977.
FIGURE 4.15: ANNUAL AVERAGE NUMBER OF THUNDER EVENTS
Source: Federal Emergency Management Agency
MAY 2006
4:24
Straight-line winds, which in extreme cases have the potential to cause wind gusts that exceed 100 miles
per hour, are responsible for most thunderstorm wind damage. One type of straight-line wind, the
downburst, can cause damage equivalent to a strong tornado and can be extremely dangerous to
aviation. Figure 4.16 shows how the frequency and strength of extreme windstorms vary across the
United States. The map was produced by the Federal Emergency Management Agency (FEMA) and is
based on 40 years of tornado history and over 100 years of hurricane history. Zone IV, the darkest area
on the map, has experienced both the greatest number of tornadoes and the strongest tornadoes. As
shown by the map key, wind speeds in Zone IV can be as high as 250 MPH.
FIGURE 4.16: WIND ZONES IN THE UNITED STATES
MAY 2006
4:25
Hailstorms are another potential damaging
outgrowth of severe thunderstorms. Early in the
developmental stages of a hailstorm, ice crystals
form within a low-pressure front due to the rapid
rising of warm air into the upper atmosphere and the
subsequent cooling of the air mass. Frozen droplets
gradually accumulate on the ice crystals until, having
developed
sufficient
weight,
they fall as
precipitation—as balls or irregularly shaped masses
of ice greater than 0.75 in. (1.91 cm) in diameter.
The size of hailstones is a direct function of the size
and severity of the storm. High velocity updraft
winds are required to keep hail in suspension in
thunderclouds. The strength of the updraft is a
function of the intensity of heating at the Earth‟s
surface. Higher temperature gradients relative to
elevation above the surface result in increased
suspension time and hailstone size. Figure 4.17
shows the annual frequency of hailstorms in the
United States.
Large hail collects on streets and grass during a
severe thunderstorm. Larger stones appear to be
nearly two to three inches in diameter. (NOAA
Photo
Library,
NOAA
Central
Library;
OAR/ERL/National Severe Storms Laboratory)
FIGURE 4.17: ANNUAL FREQUENCY OF HAILSTORMS IN THE UNITED STATES
MAY 2006
4:26
Thunderstorms are common throughout the state of Virginia, and have been known to occur during all
months of the year. In addition to the high winds associated with these events, thunderstorms can also
bring dangerous lightning that can cause fires, property damage and may cause death or serious injury.
Thunderstorms can also produce hail, which can cause varying degrees of property and crop damage.
According to the National Climatic Data Center, the region has experienced a recorded 112 severe
thunderstorm events since 1950 resulting in 1 reported death, 15 injuries and approximately $595,000 in
property damage.
Severe thunderstorms impact each jurisdiction uniformly. All building stock, infrastructure and critical
facilities are equally vulnerable to these hazards. Vulnerability maps showing infrastructure and critical
facilities that are at risk to these hazards are found in Appendix B.
SIGNIFICANT HISTORICAL EVENTS
Table 4.6 provides details of historical severe thunderstorm activity in the region as recorded by the
11
National Climatic Data Center.
TABLE 4.6: SIGNIFICANT SEVERE THUNDERSTORM EVENTS (1950-2004)
LOCATION
Virginia
Beach
Virginia
Beach
Virginia
Beach
Virginia
Beach
Norfolk
Norfolk
Suffolk
Norfolk
Virginia
Beach
Virginia
Beach
Virginia
Beach
Virginia
Beach
Virginia
Beach
Suffolk
Norfolk
Norfolk
DATE OF
MAGNITUDE DEATHS/
OCCURRENCE
(KNOTS)
INJURIES
PROPERTY
DAMAGE
7/9/1956
62 knots.
0/0
$0
8/10/1956
0 knots.
0/0
$0
4/8/1957
55 knots.
0/0
$0
3/13/1958
0 knots.
0/0
$0
2/18/1960
5/17/1960
5/21/1962
2/13/1966
N/A
N/A
N/A
N/A
0/0
0/0
0/0
0/0
$0
$0
$0
$0
2/13/1966
55 knots.
0/0
$0
1/27/1967
0 knots.
0/0
$0
4/30/1968
60 knots.
0/0
$0
7/17/1968
0 knots.
0/0
$0
7/1/1969
0 knots.
0/0
$0
7/3/1969
6/21/1970
7/16/1972
N/A
N/A
N/A
0/0
0/0
0/0
$0
$0
$0
DETAILS
No description available
11
While the Severe Thunderstorm hazard is understood to include lightning and hail as hazardous elements, tables
are provided with lightning and hail activity presented separately with the understanding that some duplication of
deaths, injuries and property damage may occur when comparing all three tables. The Southside Hampton Roads
Mitigation Planning Committee determined that the lightning hazard should be discussed and analyzed as a separate
hazard, independent from the thunderstorm discussion and analysis.
MAY 2006
4:27
LOCATION
Virginia
Beach
Virginia
Beach
Norfolk
Virginia
Beach
Norfolk
Isle of
Wight
Isle of
Wight
Isle of
Wight
Norfolk
Virginia
Beach
Virginia
Beach
Norfolk
Isle of
Wight
Norfolk
Virginia
Beach
Norfolk
Virginia
Beach
Virginia
Beach
Portsmouth
Virginia
Beach
Virginia
Beach
Virginia
Beach
Virginia
Beach
Suffolk
Isle of
Wight
Norfolk
Norfolk
Virginia
Beach
Norfolk
Norfolk
Portsmouth
Suffolk
Norfolk
Norfolk
Norfolk
Isle of
Wight
DATE OF
MAGNITUDE DEATHS/
OCCURRENCE
(KNOTS)
INJURIES
PROPERTY
DAMAGE
7/10/1973
56 knots.
0/0
$0
8/12/1973
0 knots.
0/0
$0
4/4/1974
N/A
0/0
$0
4/5/1974
0 knots.
0/0
$0
6/20/1974
60 knots
0/0
$0
6/23/1974
N/A
0/0
$0
6/23/1974
N/A
0/0
$0
8/29/1974
N/A
0/0
$0
2/24/1975
N/A
0/0
$0
3/19/1975
0 knots.
0/0
$0
3/19/1975
0 knots.
0/0
$0
3/24/1975
50 knots
0/0
$0
4/25/1975
N/A
0/0
$0
4/25/1975
55 knots
0/0
$0
4/25/1975
65 knots.
0/0
$0
7/29/1976
65 knots
0/0
$0
10/9/1976
0 knots.
0/0
$0
10/9/1976
0 knots.
0/0
$0
6/6/1977
N/A
0/0
$0
6/6/1977
0 knots.
0/0
$0
6/6/1977
53 knots.
0/0
$0
7/1/1977
0 knots.
0/0
$0
6/3/1978
0 knots.
0/0
$0
5/23/1979
N/A
0/0
$0
2/23/1980
52 knots
0/0
$0
4/4/1980
4/4/1980
52 knots
85 knots
0/0
0/0
$0
$0
4/4/1980
85 knots.
0/0
$0
7/5/1980
8/15/1980
6/16/1982
6/16/1982
6/16/1982
6/16/1982
8/11/1982
61 knots
57 knots
N/A
N/A
60 knots
60 knots
N/A
0/0
0/0
0/0
0/0
0/0
0/0
0/0
$0
$0
$0
$0
$0
$0
$0
5/8/1984
N/A
0/0
$0
DETAILS
MAY 2006
4:28
LOCATION
Portsmouth
Norfolk
Virginia
Beach
Virginia
Beach
Virginia
Beach
Isle of
Wight
Virginia
Beach
Virginia
Beach
Virginia
Beach
Norfolk
Virginia
Beach
Virginia
Beach
Virginia
Beach
Virginia
Beach
Suffolk
Isle of
Wight
Virginia
Beach
Virginia
Beach
Virginia
Beach
Virginia
Beach
Suffolk
Virginia
Beach
Virginia
Beach
Virginia
Beach
Norfolk
Virginia
Beach
Virginia
Beach
Virginia
Beach
Virginia
Beach
Virginia
Beach
DATE OF
MAGNITUDE DEATHS/
OCCURRENCE
(KNOTS)
INJURIES
PROPERTY
DAMAGE
5/8/1984
5/8/1984
N/A
57 knots
0/0
0/0
$0
$0
5/8/1984
53 knots.
0/0
$0
6/5/1985
60 knots.
0/0
$0
6/5/1985
52 knots.
0/0
$0
10/15/1985
N/A
0/0
$0
7/9/1986
69 knots.
0/0
$0
7/9/1986
69 knots.
0/0
$0
7/9/1986
55 knots.
0/0
$0
6/2/1987
60 knots
0/0
$0
7/31/1987
0 knots.
0/0
$0
6/26/1988
50 knots.
0/0
$0
3/15/1989
60 knots.
0/0
$0
3/15/1989
50 knots.
0/0
$0
3/30/1989
N/A
0/0
$0
3/31/1989
52 knots
0/0
$0
3/31/1989
65 knots.
0/0
$0
3/31/1989
54 knots.
0/0
$0
5/6/1989
0 knots.
0/1
$0
5/6/1989
0 knots.
0/0
$0
6/2/1989
N/A
0/0
$0
6/2/1989
70 knots.
0/6
$0
6/15/1989
70 knots.
0/0
$0
9/23/1989
52 knots.
0/0
$0
2/9/1990
N/A
0/0
$0
5/10/1990
0 knots.
0/0
$0
5/10/1990
0 knots.
0/0
$0
6/8/1990
0 knots.
0/0
$0
6/8/1990
0 knots.
0/5
$0
6/22/1990
60 knots.
0/0
$0
DETAILS
MAY 2006
4:29
LOCATION
Virginia
Beach
Isle of
Wight
Suffolk
Virginia
Beach
Virginia
Beach
Isle of
Wight
Isle of
Wight
Virginia
Beach
Virginia
Beach
Isle of
Wight
Virginia
Beach
Virginia
Beach
Virginia
Beach
Virginia
Beach
Isle of
Wight
Virginia
Beach
Suffolk
Virginia
Beach
Virginia
Beach
Suffolk
Virginia
Beach
Suffolk
Isle of
Wight
Virginia
Beach
Virginia
Beach
Virginia
Beach
Isle of
Wight
Suffolk
Portsmouth
Portsmouth
Portsmouth
Norfolk
DATE OF
MAGNITUDE DEATHS/
OCCURRENCE
(KNOTS)
INJURIES
PROPERTY
DAMAGE
6/22/1990
0 knots.
0/0
$0
7/1/1990
N/A
0/0
$0
7/1/1990
N/A
0/0
$0
7/1/1990
55 knots.
0/0
$0
7/1/1990
60 knots.
0/0
$0
7/11/1990
N/A
0/0
$0
7/12/1990
N/A
0/0
$0
7/12/1990
55 knots.
0/0
$0
7/12/1990
0 knots.
0/0
$0
9/7/1990
N/A
0/0
$0
9/7/1990
0 knots.
0/0
$0
10/18/1990
60 knots.
0/0
$0
3/29/1991
52 knots.
0/0
$0
3/29/1991
0 knots.
0/0
$0
5/1/1991
N/A
0/0
$0
5/1/1991
0 knots.
0/0
$0
8/4/1991
N/A
0/0
$0
8/19/1991
60 knots.
0/0
$0
8/19/1991
52 knots.
0/0
$0
9/19/1991
N/A
0/0
$0
9/19/1991
0 knots.
0/0
$0
2/15/1992
N/A
0/0
$0
7/18/1992
N/A
0/0
$0
7/18/1992
0 knots.
0/0
$0
7/18/1992
50 knots.
0/0
$0
7/27/1992
55 knots.
0/0
$0
7/31/1992
N/A
0/0
$0
7/31/1992
8/9/1992
8/28/1992
8/28/1992
8/28/1992
N/A
N/A
52 knots
N/A
55 knots
0/0
0/0
0/0
0/0
0/0
$0
$0
$0
$0
$0
DETAILS
MAY 2006
4:30
LOCATION
Isle of
Wight
Isle of
Wight
Isle of
Wight
Isle of
Wight
Isle of
Wight
Isle Of
Wight
Portsmouth
Norfolk
Airport
Isle of
Wight
DATE OF
MAGNITUDE DEATHS/
OCCURRENCE
(KNOTS)
INJURIES
PROPERTY
DAMAGE
9/4/1993
N/A
0/0
$1,000
9/22/1994
N/A
0/0
$50,000
9/22/1994
N/A
0/0
$5,000
5/19/1995
N/A
0/0
$0
11/11/1995
N/A
0/0
$75,000
1/19/1996
N/A
0/0
$0
1/19/1996
56 knots
0/0
$0
1/19/1996
54 knots
0/0
$0
3/15/1996
N/A
0/0
$0
Suffolk
3/15/1996
N/A
0/0
$0
Isle of
Wight
5/11/1996
N/A
0/0
$5,000
Windsor
6/12/1996
N/A
0/0
$2,000
Smithfield
6/15/1996
N/A
0/0
$3,000
Smithfield
6/15/1996
N/A
0/0
$3,000
Smithfield
6/24/1996
N/A
0/0
$7,000
Norfolk
6/24/1996
N/A
0/0
$10,000
Smithfield
7/18/1996
N/A
0/0
$5,000
Suffolk
7/18/1996
N/A
0/0
$3,000
Virginia
Beach
7/18/1996
0 knots.
0/0
$2,000
Portsmouth
7/31/1996
N/A
0/0
$3,000
Suffolk
7/31/1996
N/A
0/0
$4,000
7/31/1996
0 knots.
0/0
$2,000
5/1/1997
N/A
0/0
$5,000
Virginia
Beach
Isle of
Wight
DETAILS
One tree and several large branches were
down near Walters on Route 258.
Numerous trees and power lines down
throughout the county. Several barns are
damaged, and small grain silo and tractorsemi trailer overturned in the Orbit/Lake
Butler area.
Trees down on power lines on Rte. 10 and
258.
Numerous large trees were downed.
Three to six inch diameter tree limbs were
blown off of 12 trees along Route 58
between South Hampton County line and
Suffolk.
Numerous trees and power lines downed
throughout the county. The worst damage
was occurred near Rushmore and
Windsor.
Several trees uprooted onto wires near the
Blackwater River.
Numerous trees downed.
Two telephone poles downed on Route
258.
Several trees and storage shed blown
down near Route 13 and Route 616.
Roof partially blown off a house on
Minnesota Avenue.
Several trees blown down along Route 10
in Smithfield. Tree was blown down onto a
car at Benns Church Golf Course.
Numerous trees and power lines blown
down.
Several trees blown down on Atlantic
Avenue.
Several trees and power lines blown
down.
Several trees and power lines blown
down. Also, sheet metal torn off storage
building.
Large tree blown down on Back Cove
Road.
A tree fell down on house.
MAY 2006
4:31
LOCATION
Whaleyville
, Suffolk
DATE OF
MAGNITUDE DEATHS/
OCCURRENCE
(KNOTS)
INJURIES
PROPERTY
DAMAGE
7/6/1997
N/A
0/0
$10,000
7/16/1997
N/A
0/0
$2,000
7/16/1997
N/A
0/0
$5,000
Suffolk
7/19/1997
N/A
0/0
$5,000
Portsmouth
4/9/1998
N/A
0/0
$2,000
Suffolk
Airport
4/9/1998
N/A
0/0
$100,000
Suffolk
4/9/1998
N/A
0/0
$2,000
Virginia
Beach
4/9/1998
52 knots.
0/0
$10,000
Virginia
Beach
5/21/1998
82 knots.
0/0
$0
Suffolk
6/3/1998
N/A
0/0
$3,000
Windsor
6/16/1998
N/A
0/0
$3,000
Isle of
Wight
6/16/1998
N/A
0/0
$2,000
Portsmouth
6/16/1998
N/A
0/0
$2,000
Portsmouth
6/16/1998
N/A
0/0
$2,000
Portsmouth
6/16/1998
N/A
0/0
$2,000
Suffolk
6/16/1998
N/A
0/0
$3,000
Norfolk
6/16/1998
N/A
0/0
$5,000
Norfolk
6/16/1998
58 knots
0/0
$0
Virginia
Beach
6/16/1998
0 knots.
0/0
$2,000
Portsmouth
2/28/1999
N/A
0/0
$5,000
Suffolk
2/28/1999
N/A
0/0
$1,000
Norfolk
2/28/1999
70 knots
0/0
$0
Portsmouth
3/3/1999
53 knots
0/0
$0
4/23/1999
76 knots.
0/0
$0
4/23/1999
0 knots.
0/0
$5,000
5/24/1999
N/A
0/0
$2,000
Holland,
Suffolk
Norfolk
Virginia
Beach
Virginia
Beach
Suffolk
Airport
DETAILS
Several trees blown onto power lines.
Also, an old two story farm building was
collapsed.
Several trees fell down.
Numerous trees blown down.
Metal furniture blown off porch into river
and shingles blown off of houses.
Trees down on power lines.
Damage occurred to three tied down
airplanes. One of the planes was lifted up
and crashed into the other two. Also, a
panel was blown off a hangar and
temporary tents were destroyed.
Several trees fell down.
Sixty MPH straight-line wind caused
damages to the part of a metal roof of a
fire station and a storage building.
Concrete wall of the storage building was
caved in when supports gave away.
Several trees were down and a few trees
limbs fell down on houses. A car was
blown a couple hundred feet.
Several trees twisted down causing power
outages.
Several trees were down.
Numerous tree limbs and debris blown
onto Route 164 in Twin Pines area.
Dugout roof at baseball field blown off at
Churchland high school.
Four pine trees blown down at Churchland
high school.
Numerous trees were down.
Several trees down and damaged a few
homes.
Wind gust of 58 knots (67 mph) was
recorded at Norfolk International Airport.
A few trees were down.
Trees and wires were down on two
houses.
Large tree down blocking Route 460.
Wind gust of 81 mph reported by Norfolk
International Airport Tower.
Wind gust to 61 mph reported at WAVY
TV 10.
Cape Henry Tower reported wind gust of
76 knots (87 mph).
A motel on Shore Drive suffered window
damages.
Several trees were down near Suffolk
Airport.
MAY 2006
4:32
LOCATION
DATE OF
MAGNITUDE DEATHS/
OCCURRENCE
(KNOTS)
INJURIES
PROPERTY
DAMAGE
Norfolk
Virginia
Beach
Suffolk
Isle of
Wight
5/24/1999
N/A
0/0
$2,000
5/24/1999
0 knots.
0/0
$1,000
7/7/1999
N/A
0/0
$1,000
7/24/1999
N/A
0/0
$2,000
Portsmouth
7/24/1999
N/A
0/0
$1,000
Windsor
7/28/1999
N/A
0/0
$1,000
Norfolk
7/28/1999
N/A
0/0
$1,000
Virginia
Beach
7/28/1999
0 knots.
0/0
$1,000
Windsor
8/11/1999
N/A
0/0
$1,000
Suffolk
8/14/1999
N/A
0/0
$2,000
Norfolk
8/20/1999
N/A
0/0
$15,000
Suffolk
8/26/1999
N/A
0/0
$1,000
Norfolk
8/26/1999
N/A
0/0
$2,000
Isle of
Wight
5/29/2000
40 knots
1/ 3
$0
Portsmouth
6/18/2000
50 knots
0/0
$2,000
Norfolk
6/18/2000
67 knots
0/0
$100,000
Portsmouth
Virginia
Beach
6/19/2000
50 knots
0/0
$2,000
6/19/2000
50 knots.
0/0
$4,000
Norfolk
7/19/2000
50 knots
0/0
$2,000
DETAILS
Trees were down
Large tree limbs down near Salem Woods.
Large trees were down.
A large tree fell down and many tree limbs
were down.
A large tree fell on power lines.
A large tree blocked road and fell on
power lines.
Large tree was down off Kings Road near
London Bridge area.
Two large tree limbs were down on Route
460.
Roofs were blown off of a motel and an
apartment building in the East Ocean View
section of the city. Also, some structural
damage occurred to the apartment
building. Another hotel in East Ocean View
suffered minor roof damage.
Numerous power lines were down by large
tree branches.
Wind blew house off jacks and power lines
were down in Ocean View.
A powerful storm system off the North
Carolina and Virginia coast produced high
winds and waves over the James River.
One man was killed and three others were
treated for hypothermia from the still-cold
water when their 16 foot fishing boat
capsized in the James River. Effects from
the high winds did not extend very far
inland.
Trees blown down on Linear Crescent.
A severe thunderstorm hit downtown
Norfolk and Portsmouth as the OpSail
2000 Festival was ending, sending
vendors scurrying to fold tents and
spectators running for cover. Several tall
ships broke free of their moorings and
several sailors were knocked into the
Elizabeth River. Part of a brick wall was
knocked down at Bute and Botetourt
Streets, and another wall partially
collapsed at a building on Front Street in
Norfolk. A large tree fell into the Painted
Lady Restaurant at 17th and Monticello
Avenue in Norfolk.
High winds blew down several trees.
High winds blew down several trees onto
power lines at Colony Trailer Park.
Trees were blown down on power lines
and caused power outages in the Colonial
Place section of the city.
MAY 2006
4:33
LOCATION
DATE OF
MAGNITUDE DEATHS/
OCCURRENCE
(KNOTS)
INJURIES
PROPERTY
DAMAGE
Norfolk
8/1/2000
50 knots
0/0
$0
Suffolk
8/16/2000
N/A
0/0
$2,000
Suffolk
8/16/2000
50 knots.
0/0
$2,000
Isle of
Wight
12/24/2001
N/A
0/0
$15,000
4/19/2002
61 knots.
0/0
$5,000
5/2/2002
N/A
0/0
$2,000
5/13/2002
N/A
0/0
$2,000
5/13/2002
5/13/2002
5/13/2002
N/A
N/A
N/A
0/0
0/0
0/0
$2,000
$2,000
$2,000
5/13/2002
0 knots.
0/0
$2,000
Virginia
Beach
5/18/2002
0 knots.
0/0
$1,000
Portsmouth
2/22/2003
50 knots
0/0
$2,000
Norfolk
2/22/2003
50 knots
0/0
$5,000
2/22/2003
50 knots.
0/0
$2,000
2/22/2003
50 knots.
0/0
$2,000
5/8/2003
62 knots.
0/0
$0
6/7/2003
50 knots.
0/0
$5,000
Suffolk
6/13/2003
50 knots.
0/0
$2,000
Norfolk
Virginia
Beach
Isle of
Wight
7/9/2003
59 knots
0/0
$0
7/9/2003
50 knots.
0/0
$2,000
8/17/2003
50 knots
0/0
$2,000
Suffolk
8/17/2003
50 knots.
0/0
$2,000
Suffolk
8/17/2003
50 knots.
0/0
$5,000
Windsor
3/7/2004
50 knots
0/0
$2,000
Suffolk
3/7/2004
50 knots.
0/0
$4,000
Suffolk
5/23/2004
50 knots.
0/0
$2,000
Holland
5/26/2004
50 knots.
0/0
$2,000
Virginia
Beach
Suffolk
Isle of
Wight
Portsmouth
Suffolk
Norfolk
Virginia
Beach
Virginia
Beach
Virginia
Beach
Virginia
Beach
Suffolk
DETAILS
High winds blew down trees on North
Lloyd Street near downtown Suffolk. Also,
dime-sized hail fell in the Route 460/Route
13-32/North Main Street corridor near
downtown Suffolk.
High winds blew down trees at the 300
block of Drum Hill Road.
High winds with the passage of a cold
front turned camper upside down and
ripped siding off of house in the Smithfield
area.
Roof and siding peeled off of a building at
Back Bay Wildlife Refuge.
One foot diameter trees were down.
Trees were down.
Trees were down.
Trees were down.
Trees and power lines down.
Trees were down.
Numerous tree limbs were down in
Thoroughgood area. Spotter estimated a
wind gust of 55 mph.
Trees were down.
Numerous trees and power lines were
down. Also, some minor damage occurred
to houses.
Parts of a building blown into the road.
One tree down on a house in Holland
section of Suffolk.
Trees fell on power lines on Northampton
Boulevard.
Several trees were down on road.
Trees down on Everets Road. Trees down
on Edwards Road.
A tree fell down on a house.
Trees were down on Mill Swamp Road
causing power outages.
Trees were down at 2700 Block of Arches
Mill Road and along the Kings Highway
Bridge Road.
Numerous trees were down throughout
city.
Trees and power lines were down.
MAY 2006
4:34
LOCATION
DATE OF
MAGNITUDE DEATHS/
OCCURRENCE
(KNOTS)
INJURIES
PROPERTY
DAMAGE
Smithfield
6/10/2004
50 knots
0/0
$2,000
Suffolk
6/10/2004
50 knots.
0/0
$2,000
6/25/2004
50 knots.
0/0
$2,000
6/30/2004
7/7/2004
50 knots.
50 knots.
0/0
0/0
$2,000
$2,000
7/7/2004
50 knots.
0/0
$2,000
7/7/2004
50 knots.
0/0
$2,000
7/14/2004
50 knots
0/0
$2,000
7/14/2004
50 knots.
0/0
$2,000
3/8/2005
50 knots
0/0
$2,000
1/15
$595,000
Virginia
Beach
Suffolk
Suffolk
Virginia
Beach
Virginia
Beach
Smithfield
Virginia
Beach
Windsor
TOTAL
DETAILS
Three trees were down along Smithfield
Boulevard near Hunter Way.
Two trees were down in the vicinity of
Trumpet Drive and Okelly Drive.
Trees and power lines were down.
Trees down on Kings Highway.
Trees down.
Numerous trees down west of oceanfront.
Trees down along 3600 block of Virginia
Beach Boulevard.
Trees down on Route 10 and Burrells Bay
Road.
Trees down at North Landing and Princess
Anne Road.
Trees down along Central Hill Road.
Source: National Climatic Data Center
Table 4.7 shows a summary of reported hail events for the Southside Hampton Roads region between
1950 and 2004. A total of 48 hail events are known to have impacted the region since 1957, resulting in a
total of approximately $15,040,000 in property damage. The size of the recorded hailstones ranged from
0.5 inches to 2.5 inches.
TABLE 4.7: REGIONAL HAIL ACTIVITY (1950-2004)
LOCATION
Virginia Beach
Virginia Beach
Virginia Beach
Virginia Beach
Virginia Beach
Virginia Beach
Isle of Wight
Virginia Beach
Norfolk
Suffolk
Virginia Beach
Virginia Beach
Suffolk
Suffolk
Suffolk
Virginia Beach
Isle of Wight
Suffolk
Virginia Beach
Virginia Beach
Virginia Beach
Virginia Beach
Isle of Wight
DATE OF
OCCURRENCE
MAGNITUDE
PROPERTY DAMAGE
1/10/1957
4/8/1957
6/14/1963
5/7/1967
7/3/1968
10/14/1971
6/23/1974
6/23/1974
6/6/1977
8/5/1983
6/27/1985
6/2/1989
6/8/1990
7/1/1990
7/1/1990
7/1/1990
5/1/1991
5/1/1991
5/1/1991
5/1/1991
7/18/1992
7/18/1992
9/4/1993
0.67 in.
1.00 in.
0.75 in.
1.75 in.
2.00 in.
1.50 in.
1.75 in.
1.00 in.
1.75 in.
1.00 in.
0.75 in.
0.75 in.
1.75 in.
1.00 in.
2.50 in.
2.50 in.
1.75 in.
2.00 in.
1.00 in.
1.00 in.
1.00 in.
1.00 in.
1.75 in.
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$1,000
DETAILS
No details available.
MAY 2006
4:35
DATE OF
OCCURRENCE
MAGNITUDE
PROPERTY DAMAGE
Portsmouth
3/15/1996
0.50 in.
$0
Norfolk
Virginia Beach
Isle of Wight
Portsmouth
Norfolk
3/15/1996
3/15/1996
6/24/1996
6/24/1996
6/24/1996
6/24/1996
0.88 in.
1.25 in.
1.00 in.
1.75 in.
1.75 in.
0.75 in.
$0
$0
$0
$0
$0
$0
7/3/1996
7/3/1996
7/3/1996
7/18/1996
7/31/1996
3/29/1997
3/29/1997
3/29/1997
3/29/1997
5/1/1997
1.75 in.
0.88 in.
1.00 in.
1.00 in.
0.75 in.
1.00 in.
1.75 in.
1.25 in.
0.75 in.
1.75 in.
$0
$0
$0
$0
$0
$0
$0
$0
$0
$25,000
5/1/1997
5/1/1997
1.50 in.
1.75 in.
$0
$10,000,000
5/1/1997
1.75 in.
$5,000,000
7/16/1997
9/8/1997
3/21/1998
5/8/1998
5/8/1998
5/8/1998
5/8/1998
6/15/1998
2/28/1999
7/24/1999
9/7/1999
3/11/2000
3/11/2000
3/11/2000
4/17/2000
0.88 in.
1.00 in.
0.75 in.
1.00 in.
1.00 in.
0.88 in.
0.88 in.
0.75 in.
0.75 in.
0.75 in.
0.75 in.
0.75 in.
0.75 in.
1.00 in.
0.75 in.
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
$0
LOCATION
Virginia Beach
Portsmouth
Portsmouth
Virginia Beach
Portsmouth
Portsmouth
Portsmouth
Suffolk
Norfolk
Virginia Beach
Portsmouth
Suffolk
Norfolk
Virginia Beach
Norfolk
Virginia Beach
Norfolk
Isle of Wight
Suffolk
Norfolk
Virginia Beach
Suffolk
Suffolk
Portsmouth
Suffolk
Portsmouth
Norfolk
Norfolk
Smithfield
DETAILS
Marble size hail
reported in
Churchland section
of Portsmouth.
Dime size hail
occurred at Bayside
Hospital.
Many homes were
damaged by hail.
Hail caused
widespread damage
to homes,
businesses and
vehicles.
Hail caused
widespread damage
to homes,
businesses, and
vehicles.
0.75 inch diameter
hail reported by a
spotter on Carver
Road in Smithfield.
MAY 2006
4:36
LOCATION
DATE OF
OCCURRENCE
MAGNITUDE
PROPERTY DAMAGE
DETAILS
4/17/2000
0.75 in.
$0
4/21/2000
0.88 in.
$0
5/10/2000
1.75 in.
$10,000
5/27/2000
6/18/2000
6/22/2000
1.75 in.
1.00 in.
0.75 in.
$2,000
$0
$0
8/16/2000
8/16/2000
0.75 in.
0 kts.
$0
$2,000
4/15/2002
4/15/2002
4/19/2002
6/1/2002
6/1/2002
0.75 in.
1.00 in.
1.75 in.
0.75 in.
1.75 in.
$0
$0
$0
$0
$0
5/3/2003
5/29/2003
8/17/2003
8/17/2003
7/7/2004
4/23/2005
4/23/2005
1.00 in.
1.00 in.
0.75 in.
1.25 in.
0.75 in.
1.00 in.
1.00 in.
$0
$0
$0
$0
$0
$0
$0
0.75 inch diameter
hail reported just
west of Holland in
southwestern Suffolk.
0.88 inch diameter
hail reported in
Kempsville section of
Virginia Beach.
Hail up to 1.75
inches reported from
Ocean Lakes
towards the
oceanfront.
Dime sized hail fell
along Sweatt Road.
Dime-sized hail fell in
the Route 460/Route
13-32/North Main
Street corridor near
downtown Suffolk.
Dime to golf ball size
hail between Little
Creek and
Thoroughgood
sections, and west
end of Virginia Beach
oceanfront.
Suffolk
Virginia Beach
Virginia Beach
Suffolk
Virginia Beach
Suffolk
Windsor
Suffolk
Isle of Wight
Isle of Wight
Virginia Beach
Norfolk
Virginia Beach
Suffolk
Portsmouth
Isle of Wight
Virginia Beach
Norfolk
Norfolk
Virginia Beach
TOTAL
78 Events
$15,040,000
Severe thunderstorms will remain a highly likely occurrence for region. Hail will also be experienced in
the region in the future due to such storms.
MAY 2006
4:37
LIGHTNING
BACKGROUND
Lightning is a discharge of electrical energy resulting from
the buildup of positive and negative charges within a
thunderstorm, creating a “bolt” when the buildup of
charges becomes strong enough. This flash of light
usually occurs within the clouds or between the clouds
and the ground.
A bolt of lightning can reach
temperatures approaching 50,000 degrees Fahrenheit.
Lightning rapidly heats the sky as it flashes but the
surrounding air cools following the bolt. This rapid
heating and cooling of the surrounding air causes
thunder. On average, 89 people are killed each year by
lightning strikes in the United States.
Multiple
cloud-to-ground
and
cloud-to-cloud
lightning strokes observed during a nighttime
thunderstorm. (Photo courtesy of NOAA Photo
Library, NOAA Central Library; OAR/ERL/ National
Severe Storms Laboratory)
According to the National Lightning Safety Institute,
Virginia had nineteen (19) lightning-related deaths from
th
1990 to 2003 ranking the state fourteenth (14 ) in the United States in such deaths. This breaks down to
th
be 0.19 deaths per million people ranking Virginia as the twenty-seventh (27 ) most at risk state in
regards to lightning-caused death per population density.
According to the Virginia Department of Emergency Management, lightning has killed 62 people in
Virginia and injured at least 252 people between 1959 and 2003. It is believed that many additional
injuries go unreported. Nationally, from 1959 through 1994, lightning injured 13,057 people and killed
3,239, mostly men between the ages of 20 and 40. Nationally, most strikes occurred between 1 p.m. and
5 p.m. during weekends. The National Lightning Detection System identified an average of seven million
cloud-to-ground lightning strikes per year, resulting in one lightning casualty once every 86,000 strikes.
Figure 4.18 shows average lightning flash density per square mile, per year as reported by Global
Atmospherics, Inc. This graphic shows that the Virginia Beach area is a relative „hot spot” for lightning
strike activity.
MAY 2006
4:38
FIGURE 4.18: AVERAGE LIGHTNING FLASH DENSITY – 1990-1996
Source: Virginia Power, displayed on the NOAA website
According to the National Lightning Safety Institute, damage estimates reported by government agencies
(such as NCDC) do not accurately represent actual losses due to underestimation or underreporting of
actual damages. Nationwide, realistic lightning costs and losses may reach $4 to $5 billion per year
including losses associated with forest fires, insurance claims and damages to warehouses, aircraft,
electrical infrastructure and nuclear power plants.
According to the National Climatic Data Center database of storm events, 12 lightning events not directly
associated with a thunderstorm event are known to have impacted the region since 1950, resulting in 3
known deaths, 7 known injuries and over $106,000 in reported property damage, as shown in Table 4.8.
PROBABILITY OF FUTURE OCCURENCES
The Southside Hampton Roads region will continue to be at risk to the lighting hazard.
MAY 2006
4:39
TABLE 4.8: LIGHTNING ACTIVITY IN THE SOUTHSIDE HAMPTON ROADS REGION (1950-2004)
DATE OF
OCCURRENCE
DEATHS/
INJURIES
PROPERTY
DAMAGE
Smithfield
6/20/1996
0/0
$0
Portsmouth
5/6/1996
0/0
$5,000
Suffolk
4/1/1998
0/0
$4,000
Suffolk
8/1/1999
0/2
$10,000
Norfolk
6/14/1994
0/2
$0
Norfolk
6/16/1996
0/0
$2,000
Norfolk
8/26/1996
0/2
$0
Norfolk
7/30/2000
0/0
$45,000
Norfolk
8/11/2001
1/0
$0
Virginia Beach
3/15/1996
0/0
Virginia Beach
5/6/1996
0/0
Virginia Beach
7/30/2000
1/1
Virginia Beach
7/1/2004
1/0
LOCATION
$0
$40,000
$0
TOTAL
3/7
$0
DETAILS
Lightning strike caused power outages to 5,600
customers in the Smithfield area.
Lightning strike caused power surge that created
problems with city's central computer system. Also
it damaged city's radio system.
Lightning strike caused damage to a one-story
house. Several rooms had plaster blown off the
walls due to the strike's force. The roof and boxing
were also damaged.
Several homes at Blue Teal Court were struck by
lightning and several people were hospitalized.
A bolt of lightning struck and critically injured a 50year-old woman and a 38-year-old man playing in
a golf tournament at Greenbrier Country Club. Both
suffered severe burns.
Lightning strike knocked down a large oak tree that
fell onto a road.
Lightning strike seriously injured two boys who
were sitting on the bench of a picnic table beneath
a tree.
Lightning struck six homes in the Ghent and Ocean
View sections of Norfolk. One bolt hit a tree on Old
Ocean View Road and started a fire. The burning
tree then fell into a nearby home. Occupants of the
house escaped without injury.
A woman struck by lightning while on boat.
Lightning started a small fire near Kempsville Road
and Centerville Turnpike. About 2000-2500
Virginia Power customers lost power.
Lightning strike caused fires that damaged the
roofs of two houses.
Lightning struck and killed a man doing yard work
near a tree in the Great Neck Point section of
Virginia Beach.
A roofer, working at Providence Road Elementary
School, was struck by lightning and later died.
$106,000
MAY 2006
4:40
TORNADOES
BACKGROUND
A tornado is a violent windstorm characterized by a twisting, funnel-shaped cloud extending to the
ground. Tornadoes are most often generated by thunderstorm activity (but sometimes result from
hurricanes and tropical storms) when cool, dry air intersects and overrides a layer of warm, moist air
forcing the warm air to rise rapidly. The damage caused by a tornado is a result of the high wind velocity
and wind-blown debris, also accompanied by lightning or large hail. According to the National Weather
Service, tornado wind speeds normally range from 40 to more than 300 miles per hour. The most violent
tornadoes have rotating winds of 250 miles per hour or more and are capable of causing extreme
destruction and turning normally harmless objects into deadly missiles.
Each year, an average of over 800 tornadoes is
reported nationwide, resulting in an average of 80
deaths and 1,500 injuries (NOAA, 2002). They are
more likely to occur during the spring and early
summer months of March through June and can
occur at any time of day, but are likely to form in the
late afternoon and early evening. Most tornadoes
are a few dozen yards wide and touch down briefly,
but even small short-lived tornadoes can inflict
tremendous damage. Highly destructive tornadoes
may carve out a path over a mile wide and several
miles long.
Waterspouts are weak tornadoes that form over
warm water and are most common along the Gulf
Coast and southeastern states.
Waterspouts
occasionally move inland, becoming tornadoes that
cause damage and injury.
However, most
waterspouts dissipate over the open water causing
threats only to marine and boating interests.
Typically a waterspout is weak and short-lived, and
because they are so common, most go unreported
unless they cause damage.
The most comprehensively observed tornado in
history, this tornado south of Dimmitt, Texas
developed June 2, 1995 curving northward across
Texas Highway 86 where it entirely removed 300
feet of asphalt from the road tossing it more than
600 feet into an adjacent field. It also caused F4
damage at an isolated rural residence just north of
the road. (NOAA Photo Library, NOAA Central
Library;
OAR/ERL/National
Severe
Storms
Laboratory)
The destruction caused by tornadoes ranges from light to inconceivable depending on the intensity, size,
and duration of the storm. Typically, tornadoes cause the greatest damages to structures of light
construction such as residential homes (particularly mobile homes), and tend to remain localized in
impact. The Fujita-Pearson Scale for Tornadoes was developed to measure tornado strength and
associated damages, and is shown in Table 4.9.
MAY 2006
4:41
TABLE 4.9: FUJITA-PEARSON SCALE FOR TORNADOES
F-SCALE
NUMBER
INTENSITY
PHRASE
WIND
SPEED
F0
Gale
tornado
40-72
MPH
F1
Moderate
tornado
73-112
MPH
F2
Significant
tornado
113-157
MPH
F3
Severe
tornado
158-206
MPH
F4
Devastating
tornado
207-260
MPH
F5
Incredible
tornado
261-318
MPH
F6
Inconceivable
tornado
319-379
MPH
TYPE OF DAMAGE POSSIBLE
Some damage to chimneys; breaks branches off trees; pushes
over shallow-rooted trees; damages to sign boards.
The lower limit is the beginning of hurricane wind speed; peels
surface off roofs; mobile homes pushed off foundations or
overturned; moving autos pushed off the roads; attached garages
may be destroyed.
Considerable damage. Roofs torn off frame houses; mobile
homes demolished; boxcars pushed over; large trees snapped or
uprooted; light object missiles generated.
Roof and some walls torn off well-constructed houses; trains
overturned; most trees in forest uprooted.
Well-constructed houses leveled; structures with weak
foundations blown off some distance; cars thrown and large
missiles generated.
Strong frame houses lifted off foundations and carried
considerable distances to disintegrate; automobile sized missiles
fly through the air in excess of 100 meters; trees debarked; steel
re-enforced concrete structures badly damaged.
These winds are very unlikely. The small area of damage they
might produce would probably not be recognizable along with the
mess produced by F4 and F5 wind that would surround the F6
winds. Missiles, such as cars and refrigerators would do serious
secondary damage that could not be directly identified as F6
damage. If this level is ever achieved, evidence for it might only
be found in some manner of ground swirl pattern, for it may never
be identifiable through engineering studies.
Source: The Tornado Project, 2002
According to the NOAA Storm Prediction Center (SPC), the highest concentration of tornadoes in the
United States has been in Oklahoma, Texas, Kansas and Florida respectively. Although the Great Plains
region of the Central United States does favor the development of the largest and most dangerous
tornadoes (earning the designation of “tornado alley”), Florida experiences the greatest number of
tornadoes per square mile of all U.S. states (SPC, 2002). Figure 4.19 shows tornado activity in the
United States based on the number of recorded tornadoes per 1,000 square miles.
MAY 2006
4:42
FIGURE 4.19: TORNADO ACTIVITY IN THE UNITED STATES
Source: American Society of Civil Engineers
The tornadoes associated with tropical cyclones are most frequent in September and October when the
incidence of tropical storm systems is greatest. This type of tornado usually occurs around the perimeter
of the storm, and most often to the right and ahead of the storm path or the storm center as it comes
ashore. These tornadoes commonly occur as part of large outbreaks and generally move in an easterly
direction.
MAY 2006
4:43
When compared with other states, Virginia ranks 29th in number of tornado events, 25th in tornado
deaths, 26th in tornado injuries and 28th in damages. These rankings are based upon data collected for
all states and territories for tornado events between 1950 and 2003 (Storm Prediction Center, 2003).
Figure 4.20 illustrates the approximate location where confirmed tornadoes have touched down in the
region. The Fujita Scale classification of each tornado is indicated next to each occurrence.
MAY 2006
4:44
According to National Climatic Data Center records, the region has experienced 50 tornado events from
1950 through December of 2004, causing 1 death, 10 injuries and approximately $5,126,000 million in
property damage (Table 4.10). Details for each event, where available, have also been recorded in this
table.
TABLE 4.10: TORNADO EVENTS IN SOUTHSIDE HAMPTON ROADS REGION (1950-2004)
LOCATION
Norfolk
Norfolk
Portsmouth
Suffolk
Isle of
Wight
Norfolk
Norfolk
Virginia
Beach
Norfolk
Norfolk
Portsmouth
Virginia
Beach
Suffolk
Suffolk
Suffolk
Norfolk
Virginia
Beach
Norfolk
Suffolk
Virginia
Beach
Virginia
Beach
Isle of
Wight
Suffolk
Virginia
Beach
DATE OF
DEATHS/
MAGNITUDE
OCCURRENCE
INJURIES
PROPERTY
DAMAGE
4/8/1957
5/27/1957
7/10/1959
10/9/1959
F1
F
F1
F2
0/2
0/0
0/0
0/0
$250,000
$3,000
$3,000
$25,000
2/18/1960
F1
0/0
$25,000
4/8/1962
4/11/1962
F1
F0
1/0
0/1
$250,000
$3,000
10/25/1967
F1
0/0
$25,000
4/30/1968
8/10/1968
11/3/1971
F1
F1
F1
0/0
0/0
0/4
$250,000
$0
$2,500,000
7/27/1972
F1
0/2
$25,000
5/20/1973
5/28/1973
3/19/1975
6/6/1977
F0
F1
F1
F
0/0
0/0
0/0
0/0
$0
$3,000
$25,000
$25,000
10/2/1977
F
0/0
$25,000
4/4/1980
3/30/1981
F1
F2
0/1
0/0
$250,000
$250,000
7/4/1981
F1
0/0
$25,000
8/3/1988
F2
0/0
$250,000
11/28/1988
F2
0/0
$250,000
3/29/1991
F0
0/0
$25,000
8/15/1992
F0
0/0
$0
Isle of
Wight
8/6/1993
F0
0/0
$0
Isle of
Wight
10/5/1995
F0
0/0
$10,000
Isle of
Wight
10/5/1995
F0
0/0
$10,000
Smithfield
7/12/1996
F1
0/0
$25,000
DETAILS
A tornado was sighted at the Franklin
Airport. This is open area and no damage
was noted.
Brief tornado touched down uprooted a
large oak tree and several cedar/pine
trees. It tore roof off of garage.
Tornado touched down briefly in a wooded
farm area. Outbuildings were damaged;
tree tops blown out; and several trees
down just north of Burnt Mills Lake.
Small tornado damaged 10-15 homes and
several trees in the Moorfield subdivision
of Smithfield.
MAY 2006
4:45
LOCATION
DATE OF
DEATHS/
MAGNITUDE
OCCURRENCE
INJURIES
PROPERTY
DAMAGE
Norfolk
7/24/1997
F1
0/0
$400,000
Norfolk
7/24/1997
F0
0/0
$100,000
Smithfield
7/30/1997
N/A
0/0
$0
Portsmouth
7/30/1997
N/A
0/0
$0
Suffolk
7/30/1997
N/A
0/0
$0
Norfolk
7/30/1997
N/A
0/0
$0
Virginia
Beach
7/30/1997
N/A
0/0
$0
Virginia
Beach
4/9/1998
F0
0/0
$0
Norfolk
4/8/2000
N/A
0/0
$0
Norfolk
6/19/2000
N/A
0/0
$0
Virginia
Beach
7/24/2000
F0
0/0
$20,000
DETAILS
Tornado path started just south of
Poindexter Street on Guerriere Street in
Norfolk. The tornado then continued
north-northeast into the Berkley Avenue
Industrial Park before crossing into the
southern portion of Norfolk and lifting after
causing damage on Roseclair and Joyce
Streets. One business, a car wash was
destroyed, and six buildings sustained
major roof damages in the Roseclair and
Joyce Street areas of Norfolk.
Tornado first touched down west of Route
460 between Liberty Street and Indian
River Road. The tornado tracked northnortheast across Indian River Road and
across the eastern branch of the Elizabeth
River before lifting east of Harbor Park and
south of I-264. It caused minor damages
to several residential structures.
Several waterspouts were reported over
the James River.
Several waterspouts were reported just
north of Portsmouth at the intersection of
the southern Chesapeake Bay and the
James River.
Several waterspouts were reported over
the James River.
north of Norfolk over the southern
Chesapeake Bay.
north of Virginia Beach over the southern
Chesapeake Bay
A fairly long tracking tornado touched
down in portions of Chesapeake and
Virginia Beach. The tornado was first
detected in the Riverwalk section of the
city of Chesapeake around 4:30 PM. The
tornado tracked east-northeastward
through the Greenbrier section of
Chesapeake and moved through the city
of Virginia Beach along a KempsvilleRosemont-Lynnhaven axis. The tornado
damage was generally of F0 intensity
(weak) along the entire track in both
Chesapeake and Virginia Beach.
Norfolk emergency manager reported a
waterspout north of Ocean View.
A waterspout that formed over Back Bay
came ashore at Campbell Landing Road
and destroyed a 20 by 30 foot outbuilding
before dissipating. Many trees were blown
down and camper shells and lawn
furniture were tossed across the
neighborhood.
MAY 2006
4:46
LOCATION
DATE OF
DEATHS/
MAGNITUDE
OCCURRENCE
INJURIES
PROPERTY
DAMAGE
Norfolk
8/20/2000
N/A
0/0
$0
Norfolk
10/9/2000
N/A
0/0
$0
Virginia
Beach
10/9/2000
N/A
0/0
$0
Suffolk
5/21/2001
F0
0/0
$25,000
Suffolk
6/1/2001
F1
0/0
$15,000
Suffolk
2/22/2003
F0
0/0
$25,000
Virginia
Beach
8/8/2003
F0
0/0
$5,000
Norfolk
9/18/2003
F0
0/0
$0
Suffolk
6/25/2004
F1
0/0
$2,000
Suffolk
6/25/2004
F0
0/0
$2,000
Virginia
Beach
7/12/2004
N/A
0/0
$0
Virginia
Beach
8/14/2004
N/A
0/0
$0
1/10
$5,126,000
TOTAL
50 Events
DETAILS
A waterspout formed in Hampton Roads
harbor between Norfolk and Newport
News.
A waterspout formed off Ocean View
Beach, and then quickly dissipated.
A waterspout was observed by the Coast
Guard near Lynnhaven Inlet.
Tornado (F0) occurred in the 5000 block of
Manning Road. Several small outbuildings
were destroyed.
A tornado touched down near Jackson
Road about 8:10 PM. The damage path
for this tornado was approximately 100
feet wide. The tornado skipped up and
down for about a mile along a path to the
northeast of Turlington Road. It uprooted
a number of trees and took shingles off
roofs. The tornado became a funnel cloud
which touched down again around 8:15
PM just south of Sleepy Hole Road and
passed through a part of Sleepy Hole Golf
Club. The tornado continued north
northeast through Chatham Woods after
causing extensive damage along Burning
Tree Lane. The total path length in the
northern part of the county was about 1
mile long and 100 yards wide. Numerous
trees were down and a number of houses
lost siding and some roofing material.
Several 50-60 foot trees pushed over into
houses.
Tornado (F0) briefly touched down with
minor damage reported at Salem Crossing
Shopping Center. It caused minor
damage to a movie theater and adjacent
post office knocking down antennae and
some mailboxes. Fire department
observed narrow funnel and swirling
debris at the surface.
Brief F0 tornado occurred in association
with Hurricane Isabel. No damage was
reported.
F1 tornado downed numerous trees near
intersection of Route 660 and Route 668.
F0 tornado downed several trees on
Cypress Chapel Road in Whaleyville.
Funnel cloud reported between
Sandbridge Beach and Back Bay. No
damage reported.
Originally reported as a tornado, but never
touched down.
MAY 2006
4:47
It is likely that the region will continue to experience weak to moderately intense tornadoes. It is unlikely
that very strong tornadoes (F3, F4 or F5) will strike the area, though it does remain possible.
MAY 2006
4:48
WINTER STORMS AND NOR’EASTERS
BACKGROUND
A winter storm can range from a moderate snow over a period of a few hours to blizzard conditions with
blinding wind-driven snow that lasts for several days. Some winter storms may be large enough to affect
several states, while others may affect only a single community. Many winter storms are accompanied by
low temperatures and heavy and/or blowing snow, which can severely impair visibility.
Winter storms may include snow, sleet, freezing rain,
or a mix of these wintry forms of precipitation.
Sleet—raindrops that freeze into ice pellets before
reaching the ground—usually bounce when hitting a
surface and do not stick to objects; however, sleet
can accumulate like snow and cause a hazard to
motorists. Freezing rain is rain that falls onto a
surface with a temperature below freezing, forming a
glaze of ice. Even small accumulations of ice can
cause a significant hazard, especially on power lines
and trees. An ice storm occurs when freezing rain
falls and freezes immediately upon impact.
Communications and power can be disrupted for
days, and even small accumulations of ice may
cause extreme hazards to motorists and
pedestrians.
A freeze is weather marked by low temperatures,
especially when below the freezing point (zero
degrees Celsius or thirty-two degrees Fahrenheit).
Agricultural production is seriously affected when
temperatures remain below the freezing point.
A heavy layer of ice was more weight than this tree
in Kansas City, Missouri could withstand during a
January 2002 ice storm that swept through the
region bringing down trees, power lines and
telephone lines. (Photo by Heather Oliver/FEMA
News Photo)
Nor’easters are extra-tropical events that produce strong winds and precipitation in the form of heavy
rain, ice or snow. They can cause increases in tidal elevations (storm surge), wind speed, and erosion.
These cyclonic storms, called nor‟easters because of the direction of the storm winds, can last for several
days and can impact very large areas.
The presence of the Gulf Stream off the eastern seaboard in the winter season acts to dramatically
enhance the surface horizontal temperature gradients within the coastal zone. This is particularly true off
the Virginia coastline where, on average, the Gulf Stream is closest to land north of 32 degrees latitude.
During winter offshore cold periods, these horizontal temperature gradients can result in rapid and intense
destabilization of the atmosphere directly above and shoreward of the Gulf Stream. This air mass
modification or conditioning period often precedes wintertime coastal extra-tropical cyclone development.
It is the temperature structure of the continental air mass and the position of the temperature gradient
along the Gulf Stream that drives this cyclone development. As a low pressure deepens, winds and
waves can uninhibitedly increase and cause serious damage to coastal areas as the storm generally
moves to the northeast.
The coastal counties of Virginia are most vulnerable to the impacts of nor‟easters. Since the storms often
occur at night, and typically make landfall with less warning than hurricanes (due to their rapid formation
along the coast), residents may be caught at home unprepared. On the other hand, nor‟easters typically
MAY 2006
4:49
occur during the tourist off-season when fewer non-residents are visiting the coast. As with hurricanes,
structural vulnerability to nor‟easters is proportional to the strength of the structure, with mobile homes
being particularly vulnerable.
TABLE 4.11: DOLAN-DAVIS NOR’EASTER INTENSITY SCALE
STORM CLASS
BEACH EROSION
DUNE EROSION
PROPERTY
DAMAGE
OVERWASH
1
(Weak)
Minor changes
None
No
No
2
(Moderate)
Modest; mostly to
lower beach
Minor
No
Modest
3
(Significant)
Erosion extends
across beach
Can be significant
No
4
(Severe)
Severe beach
erosion and
recession
Extreme beach
erosion
Severe dune
erosion or
destruction
Dunes destroyed
over extensive
areas
On low beaches
Loss of many
structures at local
level
Loss of structures at
community- scale
5
(Extreme)
Massive in sheets
and channels
Extensive at
regional-scale;
millions of dollars
MAY 2006
4:50
Historical evidence indicates that the Southside Hampton Roads region has been impacted by varying
degrees of snow storms and ice storms over the last century. In terms of receiving measurable snowfall,
the National Climatic Data Center estimates that there is statistically an 85.8 percent probability that the
region will receive measurable snowfall in any given year; a 78.9 percent probability in winter; and a 24.4
percent probability in spring (Table 4.12).
Figure 4.21 shows the number of days (annually) with snowfall greater than one inch. Figure 4.22
shows region‟s winter storm hazard risk as determined in the Virginia State Hazard Mitigation Plan.
Winter storms impact each jurisdiction uniformly. All building stock, infrastructure and critical facilities are
equally vulnerable to these hazards. Vulnerability maps showing infrastructure and critical facilities that
are at risk to these hazards are found in Appendix B.
TABLE 4.12: PROBABILITY OF RECEIVING A MEASURABLE SNOWFALL
JURISDICTION
Isle of Wight
Norfolk
Portsmouth
Suffolk
Virginia Beach
TOTALS:
ANNUAL
PROBABILITY
WINTER
PROBABILITY
SPRING
PROBABILITY
FALL
PROBABILITY
No data
89.8%
No data
92.5%
75%
85.8%
No data
88.7%
No data
87.2%
60.7%
78.9%
No data
35.8%
No data
26.9%
10.5%
24.4%
No data
5.6%
No data
6.9%
2.1%
4.9%
Source: NOAA, National Climatic Data Center, Snow Climatology Page
According to the National Climatic Data Center, the Southside Hampton Roads region has experienced
24 significant winter storm events including snow and ice storms, extreme cold, and freezing rain since
1993 (Table 4.13). These events account for $20,120,000 in property damages for the affected areas,
which includes multiple counties. The region received presidential disaster declarations from major winter
storms in 1996 (the Blizzard of ‟96) and 2000. Some of the more significant winter storms to impact the
region in the twentieth century are discussed below.
On March 1-3, 1927 a nor'easter hit the region with high winds gusting to 62 mph at Cape Henry and 52
mph at Norfolk. Heavy snow fell across North Carolina into Virginia and travel was delayed for two to
three days. In Virginia Beach, high tide and heavy surf on March 2 inflicted considerable damage. The
beaches in some places were washed back 50 feet and denuded of the overlying sand, exposing the clay
beneath.
On April 11, 1956, a severe Nor'easter gave gale winds (greater than 40 mph) and unusually high tides
to the Tidewater Virginia area. At Norfolk, the strongest gust was 70 mph. The strong northeast winds
blew for almost 30 hours and pushed up the tide, which reached 4.6 feet above normal in Hampton
Roads. Thousands of homes were flooded by the wind-driven high water and damages were large. Two
ships were driven aground. Waterfront fires were fanned by the high winds. The flooded streets made
access to firefighters very difficult, which added to the losses.
On January 30-31, 1966, a blizzard struck Virginia and the Northeast U.S. It was the second snowstorm
to hit Virginia in a week. The first storm dumped 9 inches in Norfolk. With fresh snow on the ground, arctic
air settled in and temperatures dropped into the teens. The second storm dumped one to two feet of snow
MAY 2006
4:51
over a large part of the state. Intense winds and drifting snow continued and kept roads closed for several
days after the storm. Temperatures dropped into the single digits with some falling below zero. Wind chill
temperatures were dangerously low.
The winter of 1976-1977 was the coldest winter on the East Coast of the past century. Storms across
the state dropped a few more inches every few days to keep a fresh coating on the streets that were just
clearing from the previous storms. The average temperature for the month of January in Norfolk was
29.2°F which was 12° below normal. The prolonged cold wave caused oil and natural gas shortages and
President Carter asked people to turn thermostats down to conserve energy. The major elements of this
winter were the cold temperatures. There was little snowfall associated with this winter in the Southside
Hampton Roads region.
The “Presidents Day Storm” of February 1979 dropped 7 inches on snow on Norfolk on February 18-19
and 13 inches of snow were recorded for the entire month. The following winter, 20 inches fell in Virginia
Beach and a foot of snow fell in Norfolk in a storm that hit the region in February. On March 1, another
foot of snow fell in Norfolk and the total snowfall amount of 41.9 inches for Norfolk was the snowiest
winter ever recorded in eastern Virginia.
The “Superstorm of March ’93,” was also known as “The Storm of the Century” for the eastern United
States, due to its large area of impact, all the way from Florida and Alabama through New England.
Impacts in the Southside Hampton Roads region were not as severe, but this storm still caused major
disruption across a large portion of the country.
The “1996 Blizzard” from January 6 to January 13, 1996 affected much of the eastern seaboard. In
Virginia, the winter storm left up to 36 inches of snow in portions of the state. In the Southside Hampton
Roads region, most of the communities saw at least a foot of snow between January 6 and January 12.
Many other descriptions of historical occurrences of winter storms and nor‟easters can be found online at
http://www.vaemergency.com/newsroom/history/winter.cfm
MAY 2006
4:52
TABLE 4.13: WINTER STORM ACTIVITY IN THE SOUTHSIDE HAMPTON ROADS REGION (19982004)
LOCATION
DATE OF
OCCURRENCE
TYPE OF
EVENT
Isle of Wight
County
9
jurisdictions,
including Isle
of Wight
17
jurisdictions,
including Isle
of Wight
20
jurisdictions,
including Isle
of Wight
33
jurisdictions,
including Isle
of Wight
40
jurisdictions,
including Isle
of Wight
12/28/1993 Winter
Weather
1/6/1996 Winter
Storm
25
jurisdictions,
including Isle
of Wight
1/19/2000 Winter
Storm
7
jurisdictions,
including Isle
of Wight
1/25/2000 Winter
Storm
4
jurisdictions,
including Isle
of Wight
2/2/1996 Winter
Storm
2/16/1996 Winter
Storm
3/7/1996 Winter
Storm
12/23/1998 Ice Storm
12/3/2000
Winter
Storm
PROPERTY
DAMAGE
DETAILS
$0 No description available.
$50,000 No description available.
$0 A winterstorm tracked northeast from the gulf coast
states to off the Virginia coast. It spread a mixture of
snow, sleet and some freezing rain from the lower
Chesapeake Bay southwest into south central Virginia.
$0 A storm tracked northeast from western South Carolina
Thursday night to off the North Carolina coast Friday
morning. Then it moved off north and spread heavy
snow across Virginia.
$0 A low pressure area developed over the Carolinas and
then tracked off Virginia coast. It spread light snow
across central and eastern Virginia.
$20,000,000 A major ice storm affected central and eastern Virginia
from Wednesday into Friday. A prolonged period of
freezing rain and some sleet resulted in ice
accumulations of one half inch to one inch in many
locations. The heavy ice accumulations on trees and
power lines caused widespread power outages across
the region. Approximately 400,000 customers were
without power during the maximum outage period.
Some customers were without power for about ten
days. Many accidents occurred due to slippery road
conditions, especially bridges and overpasses. Many
secondary roads were impassable due to fallen tree
limbs or whole trees.
$0 Two to three inches of snow fell overnight as an area of
low pressure passed south of the region. The highest
amounts were measured along a line from Caroline
county in the north, through the city of Richmond, then
along the southern shore of the James River.
$20,000 A significant winter storm dropped 8 to 12 inches of
snow across portions of eastern Virginia. There was
blowing and drifting of snow from winds which gusted
over 40 mph at times. The snow mixed with sleet and
freezing rain occasionally during the late morning
hours. In Isle of Wight County, strong winds pushed the
Pagan River onto South Church Street. Isle of Wight
County snowfall totaled 7 to 8 inches.
$50,000 A winter storm struck parts of extreme southern and
southeastern Virginia. The storm affected a relatively
small area, but the areas that had snow received some
hefty totals. Windsor reported 4 inches of snowfall.
Local law enforcement agencies reported scores of
accidents, several of which involved injuries. Schools
were closed the following day.
MAY 2006
4:53
LOCATION
DATE OF
OCCURRENCE
TYPE OF
EVENT
PROPERTY
DAMAGE
27
jurisdictions,
including Isle
of Wight
2/22/2001
Winter
Storm
$0
18
jurisdictions,
including Isle
of Wight
1/2/2002
Winter
Storm
$0
19
jurisdictions,
including Isle
of Wight
12/4/2002
Winter
Storm
$0
43
jurisdictions,
including Isle
of Wight
1/6/2003
Winter
Weather/
mix
$0
27
jurisdictions,
including Isle
of Wight
1/16/2003
Winter
Storm
0
12
jurisdictions,
including Isle
of Wight
1/23/2003
Winter
Weather/
mix
$0
17
jurisdictions,
including Isle
of Wight
2/15/2003
Winter
Storm
$0
24
jurisdictions,
including Isle
of Wight
1/9/2004
Winter
Storm
$0
14
jurisdictions,
including Isle
of Wight
1/25/2004
Winter
Storm
$0
DETAILS
A winter storm produced 1 to 4 inches of snow across
south central and eastern Virginia. Local law
enforcement agencies reported numerous accidents,
some of which involved injuries. Many schools were
dismissed early on the day of the storm, and several
schools in the area were either closed or had a delayed
opening the following day due to slippery road
conditions.
A winter storm produced 8 to as much as 12 inches of
snow across south central and southeast Virginia.
Local law enforcement agencies reported numerous
accidents. Most schools in the area were closed
Thursday and Friday due to very slippery road
conditions.
A winter storm produced 1 to 4 inches of snow along
with 1/4 to 1/2 inch of ice from south central Virginia
northeast through the middle peninsula and Virginia
northern neck. Numerous trees and power lines were
reported down due to ice accumulations, resulting in
scattered power outages. Local law enforcement
agencies also reported numerous accidents. Most
schools in the area were closed Thursday and Friday
due to power outages and very slippery road
conditions.
A weak winter storm produced only a dusting to 1 inch
of snow across portions of central and eastern Virginia.
Accumulations from this storm were mostly on cars and
grassy areas, with roadways remaining generally wet
although some slush was reported.
A winter storm produced 4 to 8 inches of snow across
portions of central and eastern Virginia. Local law
enforcement agencies reported numerous accidents.
Most schools in the area were closed Friday due to
very slippery road conditions.
A winter storm produced around one inch of snow
across portions of south central and southeast Virginia.
Local law enforcement agencies reported several
accidents.
A winter storm produced 1 to 3 inches of snow, along
with sleet and 1/4 to 1/2 inch of ice accumulation,
across central and eastern Virginia. Local law
enforcement agencies reported numerous accidents.
Most schools in the area were closed Monday due to
very slippery road conditions.
Two to as much as five inches of snow fell across
portions of central, south central, and southeast
Virginia. The snow produced very slippery roadways,
which resulted in several accidents.
Two to as much as four inches of snow and sleet fell
across portions of eastern and southeast Virginia. The
snow and sleet produced very slippery roadways,
which resulted in numerous accidents and school
closings for a few days.
MAY 2006
4:54
DATE OF
OCCURRENCE
TYPE OF
EVENT
PROPERTY
DAMAGE
2/15/2004
Winter
Storm
$0
12/19/2004
Winter
Weather/
mix
$0
12/26/2004
Winter
Storm
$0
1/19/2005
Winter
Weather/
mix
$0
1/20/2005
Winter
Weather/
mix
$0
36
jurisdictions,
including Isle
of Wight
2/3/2005
Winter
Weather/
mix
$0
TOTAL
24 Events
LOCATION
22
jurisdictions,
including Isle
of Wight
43
jurisdictions,
including Isle
of Wight
10
jurisdictions,
including Isle
of Wight
43
jurisdictions,
including Isle
of Wight
41
jurisdictions,
including Isle
of Wight
DETAILS
One to three inches of snow fell across portions of
south central and southeast Virginia. The snow
produced very slippery roadways, which resulted in
several accidents and school closings for a few days.
One half inch to as much as three inches of snow fell
across central and eastern Virginia. The snow
produced slippery roadways, which resulted in several
accidents.
A winter storm produced a narrow band of six to as
much as fourteen inches of snow across the Virginia
Eastern Shore, Hampton Roads, and interior southeast
Virginia. The snow caused very hazardous driving
conditions, which resulted in numerous accidents.
Smithfield in Isle of Wight county reported 12 inches
and Isle of Wight reported 11 inches.
One half inch to as much as two inches of snow fell
across central and eastern Virginia. The snow
accidents.
One half inch to as much as three inches of snow fell
across much of central and eastern Virginia. The snow
accidents. .
One half inch to two inches of snow fell across much of
central and eastern Virginia. A few isolated areas
reported close to four inches. The snow produced
slippery roadways, which resulted in several accidents.
Smithfield in Isle of Wight county reported 2.3 inches of
snow.
$20,120,000
12
Winter storms will remain a likely occurrence for the region. While storms will be more likely to produce
small amounts of snow, sleet or freezing rain, larger storms, though less frequent in occurrence, could
also impact the region.
12
Damages are based on the methodological assumption that damages were equally distributed among impacted
counties. While this may not produce an exact estimate of property damage within the region, it is deemed sufficient
for planning purposes within this context.
MAY 2006
4:55
EROSION (COASTAL AND RIVERINE)
BACKGROUND
Erosion is the gradual breakdown and movement of land due to both physical and chemical processes of
water, wind, and general meteorological conditions. Natural, or geologic, erosion has occurred since the
Earth‟s formation and continues at a very slow and uniform rate each year. Major storms such as
hurricanes and tropical storms may cause more sudden, rapid erosion by combining heavy rainfall, high
winds, heavy surf and storm surge to significantly impact river banks and the shoreline.
As it relates to natural hazards that threaten property damage,
there are two types of erosion to be concerned: riverine erosion
and coastal erosion. The primary concern of both riverine and
coastal erosion is the gradual removal of rock, vegetation and
other sediment materials from river banks, stream beds and
shorelines that result in soil instability and possible damages to
property and infrastructure.
Riverine erosion is a long term geologic process that reshapes
river beds and stream banks as sediment is excavated and
transported downstream. Typically, it occurs faster during periods
of high velocity flows brought on by heavy rainfall, stormwater
runoff and/or dam releases. Riverine erosion is most often
mitigated through local sediment and erosion control projects, such
as the construction of armored revetments and bulkheads or the
replacement of vegetation that serves to stabilize eroding soils.
The riverine erosion hazard is also greatly minimized through the
designation of riparian buffers and the enforcement of regulatory
setbacks from eroding river banks.
Erosion threatens to damage a
waterfront home. (Photo courtesy of
FEMA)
Coastal erosion is a significant, long term hazard that threatens to
undermine waterfront homes, businesses, and public facilities along our all of our nation‟s shorelines,
eventually rendering them uninhabitable or unusable. Coastal erosion is driven by number of natural
influences such as rising sea level, large storms such as tropical storms, nor‟easters and hurricanes,
storm surge, flooding and powerful ocean waves. Manmade influences such as coastal development,
offshore dredging or shoreline stabilization projects can also exacerbate coastal erosion, even when
initially intended to minimize immediate or erosion effects. According to FEMA, coastal erosion has been
a factor in more than 25 federal disaster designations during the past twenty years.
The average annual erosion rate on the Atlantic coast is roughly 2 to 3 feet per year. States bordering
the Gulf of Mexico have the nation‟s highest average annual erosion rates (6 feet per year). That being
said, erosion rates vary greatly from location to location and year to year. Both the Atlantic and Gulf
coasts are bordered by a chain of roughly 300 barrier islands, which are composed primarily of loose
sand and are the most dynamic land masses along the open-ocean coast. Barrier island coastlines have
been retreating landward for thousands of years in response to slowly rising sea levels.
A recent study by The Heinz Center (2000), Evaluation of Erosion Hazards, states that over the next 60
years, erosion may claim one out of four houses within 500 feet of the U.S. shoreline. It also states that
nationwide, erosion may be responsible for approximately $500 million in property loss to coastal property
owners per year, including both damage to structures and loss of land. To the homeowners living within
areas subject to coastal erosion, the risk posed by erosion is comparable to the risk from flooding and
MAY 2006
4:56
other natural hazard events. While not as sudden, coastal erosion clearly influences the stability and
condition of coastal property and beaches when such other events occur.
Although some riverine erosion occurs in various locations along the rivers that flow through the
Southside Hampton Roads region, there are no riverine erosion hazard data or maps available at this
time to conduct a region-wide analysis. Riverine erosion concerns are localized in nature and are best
suited for site-specific analyses.
Coastal erosion is a significant concern in the Southside Hampton Roads region. According to the
Virginia Institute of Marine Sciences (VIMS), the Atlantic and Chesapeake Bay coasts surrounding the
area are very dynamic in terms of shoreline change and sediment transport processes. VIMS and other
agencies occasionally perform studies to determine long term shoreline change patterns for various
locations across the region. However, these studies are largely intended to track shoreline and dune
evolution through natural and manmade alterations, and not designed to determine erosion rates or areas
of coastal erosion. While the Federal Emergency Management Agency does not map erosion hazard
13
areas, it does map the highest risk areas for coastal flooding with wave action (“V zones”) . For
purposes of this analysis it can generally be assumed that areas identified as coastal high hazard zones
are also at risk to the effects of coastal erosion. While coastal flooding is typically a short term event,
coastal erosion may best be described as a relatively slow natural process occurring over the long term,
with occasional major impacts wrought by coastal storm and flooding hazards.
Another
complicating
factor
in
accurately
determining specific coastal erosion hazard areas is
the continuous implementation of shoreline
reinforcement or nourishment projects completed
by federal, state and local government agencies.
Typically, areas of high concern with regard to long
term erosion are addressed through shoreline
hardening or stabilization projects, such as
seawalls,
breakwaters
and
beach
sand
replenishment. For example, in 2002, the Virginia
Beach Erosion Control and Hurricane Protection
Project was completed, protecting more than six
miles from the imminent hazards of coastal erosion
through sand renourishment. Many other projects
have been completed in the region and still others
14
are pending approval and/or funding . The ability
to continue successfully mitigating the effects of
coastal erosion hazards throughout the region will
depend on regular shoreline monitoring and the
design and implementation of site-specific
solutions, as has been done in the past.
This photo, taken while the Virginia Beach Erosion
Control and Hurricane Protection Project was
underway, shows the significant difference between
the unimproved area and the area of the widened
beach berm already completed. (Source: City of
Virginia Beach)
HISTORICAL OCCURENCES
No significant riverine erosion events have been recorded in the region. Coastal erosion events often
occur in conjunction with hurricanes, tropical storms and nor‟easters.
13
14
For more information on FEMA V-zones, refer to the Flood hazard.
In countering the effects of coastal erosion, Virginia Beach‟s shoreline has been renourished annually since 1951.
MAY 2006
4:57
PROBABILITY OF FUTURE OCCURENCES
Over time, riverine and coastal erosion will continue to occur in the Southside Hampton Roads region.
Coastal erosion will be more immediate and severe during hurricanes, tropical storms and nor‟easters.
MAY 2006
4:58
EARTHQUAKES
BACKGROUND
An earthquake is the motion or trembling of the ground produced by sudden displacement of rock in the
Earth's crust. Earthquakes result from crustal strain, volcanism, landslides or the collapse of caverns.
Earthquakes can affect hundreds of thousands of square miles; cause damage to property measured in
the tens of billions of dollars; result in loss of life and injury to hundreds of thousands of persons; and
disrupt the social and economic functioning of the affected area.
Most property damage and earthquake-related
deaths are caused by the failure and collapse of
structures due to ground shaking. The level of
damage depends upon the amplitude and duration of
the shaking, which are directly related to the
earthquake size, distance from the fault, site and
regional geology.
Other damaging earthquake
effects include landslides, the down-slope movement
of soil and rock (mountain regions and along
hillsides), and liquefaction, in which ground soil loses
the ability to resist shear and flows much like quick
sand. In the case of liquefaction, anything relying on
the substrata for support can shift, tilt, rupture or
collapse.
Many roads, including bridges and elevated
highways, were damaged by the 6.7 magnitude
earthquake that impacted the Northridge, California
area January 17, 1994. Approximately 114,000
structures were damaged and 72 deaths were
attributed to the event. Damage costs were
estimated at $25 billion. (FEMA News Photo)
Most earthquakes are caused by the release of
stresses accumulated as a result of the rupture of
rocks along opposing fault planes in the Earth‟s
outer crust. These fault planes are typically found
along borders of the Earth's 10 tectonic plates.
These plate borders generally follow the outlines of the continents, with the North American plate
following the continental border with the Pacific Ocean in the west, but following the mid-Atlantic trench in
the east. As earthquakes occurring in the mid-Atlantic trench usually pose little danger to humans, the
greatest earthquake threat in North America is along the Pacific Coast.
The areas of greatest tectonic instability occur at the perimeters of the slowly moving plates, as these
locations are subjected to the greatest strains from plates traveling in opposite directions and at different
speeds. Deformation along plate boundaries causes strain in the rock and the consequent buildup of
stored energy. When the built-up stress exceeds the rocks' strength, a rupture occurs. The rock on both
sides of the fracture is snapped, releasing the stored energy and producing seismic waves, generating an
earthquake.
Earthquakes are measured in terms of their magnitude and intensity. Magnitude is measured using the
Richter Scale, an open-ended logarithmic scale that describes the energy release of an earthquake
through a measure of shock wave amplitude (see Table 4.14). Each unit increase in magnitude on the
Richter Scale corresponds to a 10-fold increase in wave amplitude, or a 32-fold increase in energy.
Intensity is most commonly measured using the Modified Mercalli Intensity (MMI) Scale based on direct
and indirect measurements of seismic effects. The scale levels are typically described using roman
numerals, with a I corresponding to imperceptible (instrumental) events, IV corresponding to moderate
(felt by people awake), to XII for catastrophic (total destruction). A detailed description of the Modified
Mercalli Intensity Scale of earthquake intensity and its correspondence to the Richter Scale is given in
Table 4.15.
MAY 2006
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TABLE 4.14: RICHTER SCALE
RICHTER MAGNITUDES
Less than 3.5
3.5-5.4
EARTHQUAKE EFFECTS
Generally not felt, but recorded.
Often felt, but rarely causes damage.
Under 6.0
At most slight damage to well-designed buildings. Can cause major damage to
poorly constructed buildings over small regions.
6.1-6.9
Can be destructive in areas up to about 100 kilometers across where people live.
7.0-7.9
Major earthquake. Can cause serious damage over larger areas.
Great earthquake. Can cause serious damage in areas several hundred
kilometers across.
Source: United States Geological Survey
8 or greater
TABLE 4.15: MODIFIED MERCALLI INTENSITY SCALE FOR EARTHQUAKES
SCALE
INTENSITY
DESCRIPTION OF EFFECTS
I
Instrumental
II
Feeble
Some people feel it
III
Slight
Felt by people resting; like a truck rumbling by
IV
Moderate
V
Slightly Strong
VI
Strong
VII
CORRESPONDING
RICHTER SCALE
MAGNITUDE
Detected only on seismographs
<4.2
Felt by people walking
Sleepers awake; church bells ring
<4.8
Trees sway; suspended objects swing, objects fall off
shelves
<5.4
Very Strong
Mild Alarm; walls crack; plaster falls
<6.1
VIII
Destructive
Moving cars uncontrollable; masonry fractures, poorly
constructed buildings damaged
IX
Ruinous
X
Disastrous
XI
Very Disastrous
XII
Catastrophic
Some houses collapse; ground cracks; pipes break open
Ground cracks profusely; many buildings destroyed;
liquefaction and landslides widespread
Most buildings and bridges collapse; roads, railways,
pipes and cables destroyed; general triggering of other
hazards
Total destruction; trees fall; ground rises and falls in waves
<6.9
<7.3
<8.1
>8.1
Figure 4.23 shows the probability that ground motion will reach a certain level during an earthquake. The
data show peak horizontal ground acceleration (the fastest measured change in speed, for a particle at
ground level that is moving horizontally due to an earthquake) with a 10 percent probability of
exceedance in 50 years. The map was compiled by the U.S. Geological Survey (USGS) Geologic
Hazards Team, which conducts global investigations of earthquake, geomagnetic, and landslide hazards.
MAY 2006
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FIGURE 4.23: PEAK ACCELERATION WITH 10 PERCENT PROBABILITY OF EXCEEDANCE IN
50 YEARS
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Virginia is affected by both the New Madrid Fault in Missouri and the Charleston Fault in South Carolina.
During the last 200 years, both of these faults have generated earthquakes measuring greater than 8 on
the Richter Scale. There is also an area of frequent, yet very weak, earthquake activity located to the
southwest of Charlottesville, Virginia.
Figure 4.24 shows the earthquake intensity level associated with the Southside Hampton Roads region,
based on the national U.S. Geological Survey map of peak acceleration with 10 percent probability of
exceedance in 50 years. According to this data, the entire region can be considered to be in a low
earthquake risk zone, with a peak ground acceleration value (%g) of 1 and 2.
MAY 2006
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Table 4.16 lists the 7 significant earthquake events that have impacted the Southside Hampton Roads
region as compiled from National Geophysical Data Center records for the period 1638 to 1985.
TABLE 4.16: SIGNIFICANT SEISMIC EVENTS IN THE SOUTHSIDE HAMPTON ROADS REGION
LOCATION
Norfolk
Norfolk
Norfolk
Norfolk
Norfolk
Norfolk
Norfolk
Suffolk
Suffolk
DATE OF OCCURRENCE
12/16/1811
8/28/1833
9/1/1886
2/21/1916
4/21/1918
3/1/1925
9/5/1944
9/1/1886
4/21/1918
15
MMI
5
3
5
3
2
2
3
5
2
DISTANCE FROM
EPICENTER (MILES)
1188
N/A
560
581
N/A
1339
881
527
N/A
Source: National Geophysical Data Center
Earthquakes of significant magnitude are unlikely occurrences for the Southside Hampton Roads region,
though the proximity of the region to the Charleston Fault could increase the possibility of feeling some
impact of a large earthquake if it were to occur along that fault line.
15
Modified Mercalli Intensity (MMI) scale for earthquakes.
MAY 2006
4:63
LANDSLIDES
BACKGROUND
A landslide is the downward and outward movement of slope-forming soil, rock, and vegetation, which is
driven by gravity. Landslides may be triggered by both natural and human-caused changes in the
environment, including heavy rain, rapid snow melt, steepening of slopes due to construction or erosion,
earthquakes, volcanic eruptions, and changes in groundwater levels.
There are several types of landslides: rock falls, rock
topple, slides, and flows.
Rock falls are rapid
movements of bedrock, which result in bouncing or
rolling. A topple is a section or block of rock that
rotates or tilts before falling to the slope below. Slides
are movements of soil or rock along a distinct surface
of rupture, which separates the slide material from the
more stable underlying material. Mudflows, sometimes
referred to as mudslides, mudflows, lahars or debris
avalanches, are fast-moving rivers of rock, earth, and
other debris saturated with water. They develop when
water rapidly accumulates in the ground, such as
heavy rainfall or rapid snowmelt, changing the soil into
a flowing river of mud or "slurry." Slurry can flow
Landslides can damage or destroy roads, railroads,
pipelines, electrical and telephone lines, mines, oil
rapidly down slopes or through channels, and can
wells, buildings, canals, sewers, bridges, dams,
strike with little or no warning at avalanche speeds.
seaports, airports, forests, parks, and farms. (Photo
Slurry can travel several miles from its source, growing
by Lynn Forman)
in size as it picks up trees, cars, and other materials
along the way. As the flows reach flatter ground, the
mudflow spreads over a broad area where it can accumulate in thick deposits.
Landslides are typically associated with periods of heavy rainfall or rapid snow melt and tend to worsen
the effects of flooding that often accompanies these events. In areas burned by forest and brush fires, a
lower threshold of precipitation may initiate landslides. Some landslides move slowly and cause damage
gradually, whereas others move so rapidly that they can destroy property and take lives suddenly and
unexpectedly. Among the most destructive types of debris flows are those that accompany volcanic
eruptions. A spectacular example in the United States was a massive debris flow resulting from the 1980
eruptions of Mount St. Helens, Washington. Areas near the bases of many volcanoes in the Cascade
Mountain Range of California, Oregon and Washington are at risk from the same types of flows during
future volcanic eruptions.
Areas that are generally prone to landslide hazards include previous landslide areas; the bases of steep
slopes; the bases of drainage channels; and developed hillsides where leach-field septic systems are
used. Areas that are typically considered safe from landslides include areas that have not moved in the
past; relatively flat-lying areas away from sudden changes in slope; and areas at the top or along ridges,
set back from the tops of slopes.
In the United States, it is estimated that landslides cause up to $2 billion in damages and from 25 to 50
deaths annually. Globally, landslides cause billions of dollars in damage and thousands of deaths and
injuries each year. Figure 4.25 delineates areas where large numbers of landslides have occurred and
areas which are susceptible to landsliding in the conterminous United States. This map layer is provided
in the U.S. Geological Survey Professional Paper 1183, Landslide Overview Map of the Conterminous
United States, available online at:
MAY 2006
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http://landslides.usgs.gov/html_files/landslides/nationalmap/national.html.
FIGURE 4.25: LANDSLIDE OVERVIEW MAP OF THE CONTERMINOUS UNITED STATES
MAY 2006
4:65
Figure 4.26 shows general indication of areas that may be susceptible to landslides according to the
United States Geological Survey. Minor landslide events are possible in localized, steep-sloped areas
during extremely wet conditions. Portions of eastern Isle of Wight County and Suffolk are moderately at
risk to landslides. This is an area where bluffs are present along the James River.
There is no history of significant landslide events in the region.
Landslides remain a possible occurrence in localized areas of the Southside Hampton Roads region, but
impacts from such events would likely cause minimal localized damage.
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SINKHOLES
BACKGROUND
Sinkholes are a natural and common geologic feature in areas with underlying limestone and other rock
types that are soluble in natural water. Most limestone is porous, allowing the acidic water of rain to
percolate through their strata, dissolving some limestone and carrying it away in solution. Over time, this
persistent erosive process can create extensive underground voids and drainage systems in much of the
carbonate rocks. Collapse of overlying sediments into the underground cavities produces sinkholes.
The three general types of sinkholes are:
subsidence, solution, and collapse.
Collapse
sinkholes are most common in areas where the
overburden (the sediments and water contained in
the unsaturated zone, surficial aquifer system, and
the confining layer above an aquifer) is thick, but the
confining layer is breached or absent. Collapse
sinkholes can form with little warning and leave
behind a deep, steep sided hole.
Subsidence
sinkholes form gradually where the overburden is
thin and only a veneer of sediments is overlying the
limestone.
Solution sinkholes form where no
overburden is present and the limestone is exposed
at land surface.
Collapses, such as the sudden formation of
sinkholes, may destroy buildings, roads, and
utilities. (Photo: Bettmann)
Sinkholes occur in many shapes, from steep-walled
holes to bowl or cone shaped depressions. Sinkholes are dramatic because the land generally stays
intact for a while until the underground spaces get too big. If there is not enough support for the land
above the spaces, then a sudden collapse of the land surface can occur. Under natural conditions,
sinkholes form slowly and expand gradually. However, human activities such as dredging, constructing
reservoirs, diverting surface water, and pumping groundwater can accelerate the rate of sinkhole
expansions, resulting in the abrupt formation of collapse sinkholes.
Although a sinkhole can form without warning, specific signs can signal potential development:





Slumping or falling fence posts, trees, or foundations
Sudden formation of small ponds
Wilting vegetation
Discolored well water
Structural cracks in walls, floors
Sinkhole formation is aggravated and accelerated by urbanization. Development increases water usage,
alters drainage pathways, overloads the ground surface, and redistributes soil. According to FEMA, the
number of human-induced sinkholes has doubled since 1930, insurance claims for damages as a result
of sinkholes has increased 1,200 percent from 1987 to 1991, costing nearly $100 million.
Existing soil types in the Southside Hampton Roads region are not conducive to the formation of natural
sinkholes. There is a higher potential for soil piping and/or erosion caused by leakage from drainage
pipes, culverts, etc.
MAY 2006
4:67
There have been no reported sinkhole occurrences in the region. Most sinkholes in this region are
caused by pipes underneath the ground that form cracks due to age and over time leaks erode the dirt
and soil around it.
Sinkholes remain a possible occurrence in localized areas of the region, but impacts from such events
would likely cause minimal localized damage.
MAY 2006
4:68
DROUGHT
BACKGROUND
Drought is a natural climatic condition caused by an
extended period of limited rainfall beyond that which
occurs naturally in a broad geographic area. High
temperatures, high winds and low humidity can
worsen drought conditions, and can make areas
more susceptible to wildfire. Human demands and
actions can also hasten drought-related impacts.
Droughts are frequently classified as one of four
types: meteorological, agricultural, hydrological or
socio-economic.
Meteorological droughts are
typically defined by the level of “dryness” when
compared to an average or normal amount of
precipitation over a given period of time. Agricultural
A USGS streamflow gaging station at the Ogeechee
droughts relate common characteristics of drought to
River near Eden, Georgia in July 2000 illustrates
their specific agricultural-related impacts. Emphasis
the drought conditions that can severely affect
tends to be placed on factors such as soil water
water supplies, agriculture, stream water quality,
deficits, water needs based on differing stages of
recreation, navigation and forest resources. (Photo
crop development, and water reservoir levels.
courtesy of the United States Geological Survey)
Hydrological drought is directly related to the effect
of precipitation shortfalls on surface and groundwater supplies. Human factors, particularly changes in
land use, can alter the hydrologic characteristics of a basin. Socio-economic drought is the result of
water shortages that limit the ability to supply water-dependent products in the marketplace. Figure 4.27
shows the Palmer Drought Severity Index (PDSI) summary map for the United States from 1895 to 1995.
PDSI drought classifications are based on observed drought conditions and range from -0.5 (incipient dry
spell) to -4.0 (extreme drought). As can be seen, the Eastern United States has historically not seen as
many significant long-term droughts as the Central and Western regions of the country.
FIGURE 4.27: PALMER DROUGHT SEVERITY INDEX, 1895-1995 PERCENT OF TIME IN
SEVERE AND EXTREME DROUGHT
Source: National Drought Mitigation Center
MAY 2006
4:69
Drought typically impacts a large area that cannot be confined to geographic boundaries; however, some
regions of the United States are more susceptible to drought conditions than others. According to the
Palmer Drought Severity Index (PDSI) Summary Map for the United States, the Commonwealth of
Virginia as a whole is in a zone of 5 percent to 9.99 percent PDSI less than or equal to -3 (-3 indicating
severe drought conditions) meaning that drought conditions are a relatively low to moderate risk for the
Southside Hampton Roads region. Furthermore, it is assumed that the region would be uniformly
exposed to this hazard and that the spatial extent of that impact would potentially be large. It is important
to note however, that drought conditions typically do not cause significant damage to the built
environment.
The drought of record for Virginia occurred in 1931 when the statewide average rainfall amount was 7.64
inches compared to an average mean rainfall amount of 17.89. This was during this period that also saw
the Great Dust Bowl that helped lead to the Great Depression.
Since 1993, the National Climatic Data Center has recorded only 2 instances of drought to impact the
16
Southside Hampton Roads region (Table 4.17). Though instances are recorded on a monthly basis by
the National Climatic Data Center, events are usually part of ongoing drought conditions that last several
months or years.
In addition to this official drought record, periods of drought-like conditions are also known to have
impacted the region in 200, 2002, 2003 and 2005. Water restrictions have been put into place as far back
as three years and shallow wells are known to have lost water in and around the region.
According to State of Virginia records, a declaration of a State of Emergency Due to Extreme Drought
Conditions was executed by the Governor of Virginia on August 30, 2005. The Executive Order was to
be effective from August 30, 2002 through June 30, 2003. Isle of Wight County is currently (2005)
seeking federal disaster drought aid because of drought conditions effecting crop production.
TABLE 4.17: OCCURRENCES OF DROUGHT IN THE SOUTHSIDE HAMPTON ROADS REGION
(1993-2004)
LOCATION
17
jurisdictions,
including
Isle of Wight
20
jurisdictions,
including
Isle of Wight
DATE OF
OCCURRENCE
10/31/1993
DETAILS
Unusually dry weather during the summer and early fall led to many communities
in southeastern Virginia to place water conservation measures into effect in
October 1993.
9/1/1997
A very dry period from May through September resulted in drought-like conditions
across much of central and eastern Virginia. Monthly rainfall departures from
normal for Norfolk included: -2.21 inches in May, -2.73 inches in June, -3.05 inches
in August, and -1.93 inches in September. This caused significant crop damage
throughout much of the area which was estimated to be around $63.8 million.
16
Drought occurrences recorded by the National Climatic Data Center are not necessarily unique events, as many
instances of drought persist through multiple reporting periods. This is reflected in the details provided for some longenduring occurrences in Table 4.17.
MAY 2006
4:70
Based on current and seasonal outlook drought maps available through the National Weather Service‟s
17
Climate Prediction Center and the National Drought Mitigation Center , there is no concern for imminent
or forecasted drought occurrences. However, based on past events, it certainly remains possible over
the long-term that the Southside Hampton Roads region will experience recurring drought conditions
when precipitation falls below normal for extended periods of time. Based on climate data, the region will
likely continue to experience occasional periods of extreme heat, but not nearly as severe as other
regions of the country.
17
Current and seasonal drought outlook maps are made available by the National Drought Mitigation Center at
www.drought.unl.edu/dm/index.html.
MAY 2006
4:71
WILDFIRE
BACKGROUND
A wildfire is any fire occurring in a wildland area (i.e., grassland, forest, brush land) except for fire under
18
prescription. Wildfires are part of the natural management of the Earth‟s ecosystems, but may also be
caused by natural or human factors. Over 80 percent of forest fires are started by negligent human
behavior such as smoking in wooded areas or improperly extinguishing campfires. The second most
common cause for wildfire is lightning.
There are three classes of wildland fires: surface fire,
ground fire, and crown fire. A surface fire is the most
common of these three classes and burns along the
floor of a forest, moving slowly and killing or
damaging trees. A ground fire (muck fire) is usually
started by lightning or human carelessness and
burns on or below the forest floor. Crown fires
spread rapidly by wind and move quickly by jumping
along the tops of trees. Wildland fires are usually
signaled by dense smoke that fills the area for miles
around.
On Sunday, August 6, 2000, several forest fires
State and local governments can impose fire safety
converged near Sula, Montana, forming a firestorm
regulations on home sites and developments to help
that overran 100,000 acres and destroyed 10
curb wildfire. Land treatment measures such as fire
homes. Temperatures in the flame front were
access roads, water storage, helipads, safety zones,
estimated at more than 800 degrees. (Photo by
buffers, firebreaks, fuel breaks, and fuel
John McColgan/U.S. Forest Service Firefighter)
management can be designed as part of an overall
fire defense system to aid in fire control. Fuel
management, prescribed burning, and cooperative land management planning can also be encouraged to
reduce fire hazards.
Fire probability depends on local weather conditions, outdoor activities such as camping, debris burning,
and construction, and the degree of public cooperation with fire prevention measures. Drought conditions
and other natural disasters (hurricanes, tornadoes, etc.) increase the probability of wildfires by producing
fuel in both urban and rural settings. Forest damage from hurricanes and tornadoes may block interior
access roads and fire breaks, pull down overhead power lines, or damage pavement and underground
utilities.
Many individual homes and cabins, subdivisions, resorts, recreational areas, organizational camps,
businesses, and industries are located within high fire hazard areas. The increasing demand for outdoor
recreation places more people in wildlands during holidays, weekends, and vacation periods.
Unfortunately, wildland residents and visitors are rarely educated or prepared for the inferno that can
sweep through the brush and timber and destroy property in minutes.
In July 2003, the Virginia Department of Forestry released a GIS-based wildfire risk assessment for the
Commonwealth of Virginia. While this assessment is not recommended for site-specific determinations of
18
Prescription burning, or “controlled burn,” undertaken by land management agencies is the process of igniting fires
under selected conditions, in accordance with strict parameters.)
MAY 2006
4:72
wildfire vulnerability, the data was utilized in this Plan as an indicator of potential areas of wildland/urban
interface concern within the Southside Hampton Roads region, as shown in Figure 4.28. Essentially,
potential wildfire risk areas are presented in three categories indicating the relative level of threat to the
community: High, Moderate and Low.
There are 679 areas that are classified High wildfire threat areas. When compared with aerial imagery it
appears that these areas are lightly developed wooded areas, including some marshland and other forms
of undeveloped land. There are 563 relatively large areas that are classified as Moderate wildfire threat
areas. These areas include both undeveloped and developed land. Most of the land area of Isle of Wight
County and the western two-thirds of Suffolk have been classified as Moderate or High wildfire threat
areas. Much of the remainder of the region, including most of Portsmouth, Norfolk and Virginia Beach,
are classified as Low wildfire threat areas. This includes heavily developed commercials areas and
several residential areas. These more heavily developed areas represent a slightly greater threat with
regard to the spread of urban fires.
According to Virginia Department of Forestry records, the region experiences an average of 12 wildfire
events per year, the majority of which are caused by open burning, arson and smokers. The majority of
recorded events have taken place in Isle of Wight County and no events have been recorded in
Portsmouth and Norfolk. Only minor property damages—generally amounting to less than $15,000 per
year—have been recorded as resulting from wildfire events. Table 4.18 shows the damages of wildfire
events in the region between 1995 and 2002.
TABLE 4.18: OCCURRENCES OF WILDFIRE IN THE SOUTHSIDE HAMPTON ROADS REGION
JURISDICTION
Virginia Beach
YEAR
FREQUENCY
BURNED ACRES
DAMAGE
1995
1996
1
1
10
0.5
$0
$0
1997
2001
2
4
8
28
225
263.5
$0
$0
$0
1995
10
17.5
$0
1996
1997
3
8
1.25
8.5
$0
$500
1998
1999
4
3
9
1.5
$600
$0
2000
2001
5
17
50
6.5
61.65
105.9
$3,000
$0
$4,100
1995
14
154.7
$33,750
1996
1997
2
5
121
132
$8,000
$20,960
1999
2000
3
2
10.5
30
$5,400
$0
2001
1
27
38
486.2
$3,000
$71,110
85
855.6
$75,210
Virginia Beach Total
Isle of Wight County
Isle of Wight County Total
Suffolk
Suffolk Total
TOTAL
Source: Virginia Department of Forestry
MAY 2006
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Wildfires remain a highly likely occurrence for the region, though most will likely continue to occur in less
urban areas and be small in size before being contained and suppressed.
MAY 2006
4:74
DAM / LEVEE FAILURE
BACKGROUND
Worldwide interest in dam and levee safety has risen significantly in recent years. Aging infrastructure,
new hydrologic information, and population growth in floodplain areas downstream from dams and near
levees have resulted in an increased emphasis on safety, operation and maintenance.
There are approximately 80,000 dams in the United
States today, the majority of which are privately
owned.
Other owners include state and local
authorities, public utilities and federal agencies. The
benefits of dams are numerous: they provide water
for drinking, navigation and agricultural irrigation.
Dams also provide hydroelectric power, create lakes
for fishing and recreation, and save lives by
preventing or reducing floods.
Though dams have many benefits, they also can
pose a risk to communities if not designed, operated
and maintained properly. In the event of a dam
failure, the energy of the water stored behind even a
small dam is capable of causing loss of life and great
property damage if development exists downstream
of the dam. If a levee breaks, scores of properties
are quickly submerged in floodwaters and residents
may become trapped by this rapidly rising water.
The failure of dams and levees has the potential to
place large numbers of people and great amounts of
property in harm‟s way.
Lake Burnt Mills in Suffolk. (Photo courtesy of City
of Suffolk)
MAY 2006
4:75
19
According to the National Inventory of Dams maintained by the U.S. Army Corps of Engineers , there are
37 major dams located in the Southside Hampton Roads region (Table 4.19). Major dams are defined as
dams being 50 feet or more in height, or with a normal storage capacity of 5,000 acre-feet or more, or
with a maximum storage capacity of 25,000 acre-feet or more. Of the major dams located in the region,
three are classified as “high” hazards where failure or mis-operation of the dam could cause loss of
human life. It is important to note that these hazard classifications are not related to the physical
condition or structural integrity of the dam (nor the probability of its failure) but strictly to the potential for
adverse downstream effects if the dam were to fail.
The state regulatory agency for dams is the Virginia Department of Conservation and Recreation through
the Dam Safety and Floodplain Management Program.
TABLE 4.19: MAJOR DAMS IN THE SOUTHSIDE HAMPTON ROADS REGION
NAME OF DAM
HAZARD CLASSIFICATION
YEAR BUILT
NORMAL
STORAGE
(ACRE FEET)
High
High
High
Significant
Low
Significant
1942
1963
1959
1962
1921
1912
7,449
14,620
6,372
1,000
10,600
6,025
Lake Burnt Mills Dam
Western Branch Dam
Lake Mead Dam
C-Pond Dam
Lake Prince Dam
Lake Cohoon Dam
Source: National Inventory of Dams
Figure 4.29 shows the location of all major and state-regulated dams in the region, and notes which of
those are classified as high, intermediate and low hazard.
In Suffolk, during Hurricane Floyd in 1999, Speight‟s Run spillway was compromised rendering Turlington
Road impassable. Other dams in Suffolk were overtopped by what was reported as 8 feet of water.
There is no other record of any damages, deaths or injuries associated with dam failure in the Southside
Hampton Roads region.
Dam failure remains an unlikely occurrence for all major and non-regulated dams in the Southside
Hampton Roads region. The Virginia Department of Conservation and Recreation is tasked with
monitoring the routine inspection and maintenance of those dams that present the greatest risk or are in
need of structural repair.
19
The National Inventory of Dams was developed by the U.S. Army Corps of Engineers in cooperation with FEMA's
National Dam Safety Program. The full inventory contains over 75,000 dams, of which 7,700 are classified as major,
and is used to track information on the country's water control infrastructure.
MAY 2006
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TSUNAMI
BACKGROUND
The word tsunami is Japanese and means “harbor wave.” A tsunami is one or a series of great waves
that are created by an earthquake, landslide, volcanic eruption, submarine earthquake or other undersea
disturbances. From the area of disturbance, tsunami waves will travel outward in all directions. Tsunamis
can originate hundreds or even thousands of miles away from coastal areas. A tsunami is not the same
as a tidal wave.
The time between wave crests may be five to 90
minutes and the open ocean wave speed may
average 450 miles per hour. As tsunami waves
approach shallow coastal waters, they appear to
be of normal size. Although the waves slow down
as they reach shallow water, the energy remains
constant. When tsunami waves crash into the
shoreline, they may be as high as 100 feet. Areas
at greatest risk are less than 50 feet above sea
level and within one mile of the shoreline. Rapid
changes in the ocean water level may indicate that
a tsunami is approaching. Most deaths during a
tsunami are the result of drowning. Associated
risks include flooding, polluted water supplies, and
damaged gas lines.
Tsunami Hazard Zone signs are posted at coastal
access points or other low-lying areas that would
clearly be vulnerable to a large, locally generated
tsunami. Signs are placed at locations agreed upon
by local and state governmental authorities.
Tsunami Evacuation Route markers are used to
designate the evacuation routes established by
local jurisdictions in cooperation with emergency
management officials. (Photos courtesy of
Washington State Department of Transportation)
In the United States, tsunamis have historically
affected the West Coast (Figure 4.30), but the
threat of tsunami inundation is also possible on the Atlantic Coast. Pacific Ocean tsunamis are classified
as local, regional, or Pacific-wide. Regional tsunamis are most common. Pacific-wide tsunamis are much
less common, with the last one being recorded in 1964, but are larger waves that have high potential to
cause destruction.
The Pacific Tsunami Warning Center was established in 1949 at Ewa Beach, Hawaii to monitor
conditions in the Pacific Ocean and to provide warnings in case of tsunamis. According to the Pacific
Tsunami Warning Center Laboratory in Novosiirsk, 796 tsunamis were observed or recorded in the Pacific
Ocean between 1900 and 2001. Approximately 117 caused casualties and damage and at least nine
caused widespread destruction throughout the Pacific. The greatest number of tsunamis during any oneyear was 19 in 1938, but all were minor and caused no damage. There was no single year of the period
that was free of tsunamis.
MAY 2006
4:77
FIGURE 4.30: PRIMARY TSUNAMI HAZARD AREAS
There is no historical evidence of tsunami events directly affecting the Southside Hampton Roads region.
However—although tsunamis are more frequently associated with Pacific Rim states—historical evidence
does indicate that tsunamis have affected the Eastern United States. In fact, 40 tsunamis and tsunami20
like waves have been documented in the Eastern United States since 1600 .
Tsunami events along the East Coast are not the result of traditional sources of tsunami waves (i.e.,
subduction zones such as the Cascadia Subduction Zone), but rather are typically the result of slumping
or landsliding associated with local earthquakes or with wave action associated with strong storms such
as hurricanes. Other possible causes of tsunami-like activity along the East Coast could include
explosive decompression of underwater methane deposits, the impact of a heavenly body (i.e., an
asteroid, comet or oceanic meteor splashdown) or a large underwater explosion. One significant
contributing factor to tsunami-related damage is the massive amount of moving debris possible during a
tsunami event—including manmade debris such as boats and also on-shore debris as the tsunami strikes
land.
20
This was documented in an article written by representatives from the National Geophysical Data Center in Volume
20, Number 3 of The International Journal of The Tsunami Society.
MAY 2006
4:78
To cite one commonly referenced example in terms of Atlantic tsunamis, a severe earthquake registering
7.2 on the Richter Scale on November 18, 1929 in the Grand Banks of Newfoundland generated a
tsunami that caused considerable damage and loss of life at Placentia Bay, Newfoundland and is also
known to have impacted upon the New England shoreline and was recorded as far south as Charleston,
South Carolina. Tsunamis were also generated by the Charleston Earthquake of 1886 and the New
Madrid earthquakes of 1811 and 1812. Additionally, a magnitude 8 earthquake in November 1755 may
have caused 10-foot waves along the East Coast.
Two off-shore areas are currently under investigation according to a 2002 National Geophysical Data
Center report. One area of interest consists of large cracks northeast of Cape Hatteras that could foretell
of the early stages of an underwater landslide that could result in a tsunami. The other area of interest
consists of submarine canyons approximately 150 kilometers from Atlantic City, New Jersey. Significant
factors for consideration with regard to these areas are recent discoveries along the East Coast that
demonstrate the existence of pressurized hydrates and pressurized water layers in the continental shelf.
This has produced speculation among the scientific community on possible triggers that could cause
sudden and perhaps violent releases of compressed material that could factor into landslide events and
the resulting tsunami waves.
There is still much uncertainty as to the severity of the tsunami threat to the East Coast. With only 40
events recorded since 1600, the probability of future occurrences, while possible, is unlikely. However,
this does not mean that jurisdictions in the region should not plan for a tsunami occurrence.
MAY 2006
4:79
EXTREME TEMPERATURES
BACKGROUND
Extreme heat is defined as temperatures that hover ten degrees or
more above the average high temperature for the region and last for
several weeks. Humid conditions may also add to the discomfort of
high temperatures. Health risks from extreme heat include heat
cramps, heat fainting, heat exhaustion and heat stroke. According to
the National Weather Service, heat is the leading weather-related
killer in the United States and has killed more people than lightning,
tornadoes, floods and hurricanes combined in the last 10 years.
However, most deaths are attributed to prolonged heat waves in large
cities that rarely experience hot weather. The elderly and the ill are
most at-risk, along with those who exercise outdoors in hot, humid
weather.
Photo courtesy of Environmental
Protection Agency
Extreme cold is generally associated with extreme winter storms. Extreme cold is a deceptive killer as it
indirectly causes injury and death resulting from exhaustion and overexertion, hypothermia and frostbite
from wind chill and asphyxiation.
According to the Office of the Chief Medical Examiner for the Commonwealth of Virginia, there were 30
deaths recorded in Virginia that were the result of extreme heat or cold. Summertime temperatures in the
Southside Hampton Roads region can easily climb into the high 90 to low 100 degree range with high
humidity rates. The region is also vulnerable to extreme winter weather occurrences that can bring
extreme cold temperatures and wind-chill.
While temperature extremes occur fairly frequently in the region, the National Climatic Data Center
(NCDC) has only recorded two extreme temperature events recorded that have impacted the region. The
first was in August of 1995 and the second was in May of 1996. There are no reported instances of
extreme cold weather recorded by NCDC.
PROBABILITY OF FUTURE EVENTS
It is possible that the Southside Hampton Roads region will experience periods of extreme temperatures
in the future.
MAY 2006
4:80
DATA SOURCES
The following primary data sources were among those used to collect the information presented in this
section.
American Society of Civil Engineers (ASCE), “Facts About Windstorms”
(www.windhazards.org/facts.cfm)
Bureau of Reclamation, U.S. Department of the Interior
(www.usbr.gov/)
Federal Emergency Management Agency (FEMA)
(www.fema.gov)
Lin Cao, Wei-Ning Xiang, and Joseph C. Wilson, Department of Geography and Earth Sciences University of North
Carolina at Charlotte
(www.lightningsafety.com/nlsi_lhm/GIS_study.html)
National Climatic Data Center (NCDC), U.S. Department of Commerce, National Oceanic and Atmospheric Administration
(http://lwf.ncdc.noaa.gov/oa/ncdc.html)
National Drought Mitigation Center, University of Nebraska-Lincoln
(www.drought.unl.edu/index.htm)
National Geophysical Data Center
(www.ngdc.noaa.gov)
National Hurricane Center, National Oceanic & Atmospheric Administration (NOAA)
(www.nhc.noaa.gov)
National Lightning Safety Institute
(www.lightningsafety.com)
National Severe Storms Laboratory (NSSL), U.S. Department of Commerce, National Oceanic and Atmospheric
Administration
(www.nssl.noaa.gov)
National Weather Service (NWS), U.S. Department of Commerce, National Oceanic and Atmospheric Administration
(www.nws.noaa.gov)
North Carolina Geological Survey
(www.geology.enr.state.nc.us)
Storm Prediction Center (SPC), U.S. Department of Commerce, National Oceanic and Atmospheric Administration,
National Weather Service
(www.spc.noaa.gov)
The Tornado Project, St. Johnsbury, Vermont
(www.tornadoproject.com)
United States Geological Survey (USGS), U.S. Department of the Interior
(www.usgs.gov)
MAY 2006

Section 4: Hazard Analysis

Transcription

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