Resolution in Support

TOWN OF OAK ISLAND
Agenda Item: New Business 6
TOWN COUNCIL
Date:
May 7, 2015
AGENDA ITEM MEMO
Issue: Resolution of Support for the City of Boiling Spring Lakes’ Planned Spillway
Project
Department: Admin
Presented by: Lisa Stites, Town Clerk
Presentation: a Power Point the City of Boiling Spring Lakes presented to Brunswick
County is included in the packet
Estimated Time for Discussion: 10 minutes
Subject Summary: The City of Boiling Spring Lakes is pursuing a new spillway project in an
attempt to control flooding on N.C. 87. Boiling Spring Lakes Commissioner Mary Stillwell
contacted Oak Island staff to request the Town Council lend its support to the project since the
City is seeking grant funding. No money is being requested from the Town of Oak Island, merely
the Town’s support for the project. A Resolution of support is included for Council’s
consideration.
Attachments:
 Resolution of Support for the City of Boiling Spring Lakes’ Planned Spillway Project
 Boiling Spring Lakes’ presentation to Brunswick County
Recommendation/Action Needed: Staff recommends Council adopt the Resolution as
presented.
Suggested Motion: I make a motion to adopt the Resolution of Support for the City of Boiling
Spring Lakes’ Planned Spillway Project
Funds Needed: None.
Follow up Action Needed: If the Resolution is adopted, staff will forward it to the appropriate
parties.
RESOLUTION IN SUPPORT OF THE
CITY OF BOILING SPRING LAKES’ PLANNED
SPILLWAY PROJECT
WHEREAS, the City of Boiling Spring Lakes is seeking grant funding to help fund a new
spillway project for N.C. 87; and
WHEREAS, heavy rains from thunderstorms and tropical storms often causes flooding on N.C.
87; and
WHEREAS, the City of Boiling Spring Lakes has a plan to install a new spillway aimed at
correcting the flooding problem on this important thoroughfare; and
WHEREAS, travel on N.C. 87 is important to many in southeastern Brunswick County, not just
the residents of Boiling Spring Lakes; and
WHEREAS, N.C. 87 is one of the few evacuation routes available to Oak Island residents and
visitors in the event an evacuation is mandated ahead of a hurricane; and
WHEREAS, the Town of Oak Island appreciates the opportunity to lend its support to this
much-needed project which has the potential to help thousands of people travel away from the
coast and to safer areas before a hurricane makes landfall; and
WHEREAS, the Town of Oak Island joins the City of Boiling Spring Lakes in requesting
funding for this project.
NOW, THEREFORE BE IT RESOLVED that the Town of Oak Island hereby officially
supports the spillway project and requests that grant funding be allocated as the City of Boiling
Spring Lakes requests.
Adopted this the 12th day of May, 2015.
____________________________________
Mayor Betty W. Wallace
Attested: ________________________________
Lisa P. Stites, CMC
Town Clerk
THE NEED FOR AN ADDITIONAL SPILLWAY
AT THE SANFORD DAM
BOILING SPRING LAKES, NC
Presentation for
The Brunswick County Commissioners
April 20, 2015
The Sanford Dam
• Earth Dam constructed in 1961
• Drainage area of 6,381 acres (10 sq. miles)
• Length of 1584 feet
• Structural height of 30 feet
• Impounds 285 acres of water
• Maximum storage of 3,600 acre-feet
• Designated as a medium size dam
• Classified as “High Hazard”
What is a High Hazard dam?
• Class C (High Hazard) includes dams located where
failure will likely cause loss of life or serious damage to
homes, industrial and commercial buildings, important
public utilities, primary highways, or major railroads.
Dam Hazards Classification
Hazard
Classification
Low
Description
Quantitative Guidelines
Interruption of road service, low
volume roads
Less than 25 vehicles per day
Economic damage
Less than $30,000
Damage to highways, Interruption of 25 to less than 250 vehicles
service
per day
Intermediate
High
Economic damage
$30,000 to less than $200,000
Loss of human life*
Probable loss of 1 or more
human lives
Economic damage
More than $200,000
*Probable loss of human life due to
breached roadway or bridge on or
250 or more vehicles per day
below the dam.
Statistics from NC Dam Safety
“Emergency Action Planning (EAP) Website”
Most dam failure fatalities are not the result of large dams.
Most fatalities are the result of small dam failures.
Dam failures resulting in fatalities:
• 86% of the fatalities have resulted from dams between 20 and 49 feet
in height
• 47% of the fatalities have resulted from dams with a drainage area
less than 2 square miles
• 75 % of the fatalities have resulted from dams with a drainage area
less than 10 square miles
• 7 dams had less than 300 acre-feet of reservoir storage area
This description fits many of North Carolina's dams
What our dam looks like today
Crest elevation 39.0 ft.
Some definitions
A 100-year flood
 a flood event that has a 1% probability of occurring in
any given year.
Probable Maximum Precipitation (PMP)
"...the theoretical maximum precipitation for a given
duration under modern meteorological conditions."
The theoretically greatest depth of precipitation for a
given duration that is physically possible over a particular
drainage area at a certain time of year
NORTH CAROLINA DAM SAFETY LAWS AND REGULATIONS
Three main concerns
1. Worst case scenario
• The Dam is overtopped at elevation 39.0 ft. and we lose the
impoundment with potential loss of life and property.
2. Excessive flooding
• We cannot keep pace with the watershed and flooding damages
roads, property, and eliminates Route 87 as an evacuation route for
communities south of BSL.
3. Creation of “sink holes”
• Current use of the gates to adjust lake levels in advance of storms
helps to create or accelerate the formation of sink holes. The new
spillway will maintain consistent levels during storms, without
manual operation. No need to depress water by 2 feet!
What could happen after overtopping
Evacuation Routes – 87, 211 and 133
Users:
Oak Island
Caswell Beach
Southport
St. James
Boiling Spring Lakes
Military Ocean Terminal Sunny Point
Brunswick Nuclear Plant/ Duke Energy
Route 87 – Our hurricane evacuation route!
2005, Tropical Storm Tammy
2005, Hurricane Ophelia
1999, Hurricane Floyd
1998, Hurricane Bonnie
1996, Hurricane Bertha
1996, Hurricane Fran
Road Elevation 34.4 ft
Other key roads flood at this location
• Isolate Residents
• Prevent Emergency
Services Response
 EMS facility is
located on north
side of Rt. 87
• Examples:
 Boiling Spring Rd
(SR1539)
 Fairway Dr.
 South Shore Dr.
 Elm Rd
Sinkholes have drained the lake
Impact on our community
How do we operate our existing gates?
• Existing gates in the outlet structure are manually operated to
maintain consistent lake levels (not recommended).
• Repeated manual operation creates future risk of gate failures.
• “Drain down” rates limited to 1 ft./day by NC Dam Safety, to prevent
slope impacts along the lake edge.
• Safety issue - equipment cannot be operated during rainfall due to
lightning shock hazard. So we predict when to lower levels.
• New spillway “open top” will enable consistent water levels without
manual operation!
• Outlet Control
New Spillway
Top of Dam
Existing Spillway
Discharge Pipes
Four (4) new
discharge pipes of
60” Diameter
Endorsements
• Wilmington District, US Army Corps of Engineers
“There is real potential for the dam to be overtopped for storms just
above the 100-year event threatening the integrity of the dam”
• Progress Energy Brunswick Nuclear Plant
“We support and endorse Boiling Spring Lake’s effort to increase
Sanford Dam’s spillway capacity, which is necessary to eliminate the
blockage of Highway 87”
• Brunswick County Department of Energy Management
• Brunswick County Commissioners (in 2008)
What have we spent in the past?
Prior Work
Year
Approximate
Expenditures
Install a grout curtain, recoat the inside of original 54" pipes,
install pipe couplings, gate modifications and install subdrains
1978
$100,000 (estimated)
Re-lining the original pipes with 40" inserts and grouting void
spaces between
1989
$92,000
Adding pipe extensions, grouting, and toe drain installation
1991
$75,000
Reconstruction of the downstream face of the dam at the
spillway
2001
$124,000
Install four (4) new hydrogates replaced at the existing spillway
2007
$110,000
Engineering Design services for the new Spillway
2013
$130,000
Approximate Total of These Efforts
$630,000
Funding This Critical Project
Partnership
% Participation
Boiling Spring Lakes
Brunswick County
25%
25% - 50%
Estimated Contributions
$500,000 (dedicated already)
$500,000 - $1,000,000
State of North Carolina
?
?
Federal Agencies
?
?
Estimated Project Cost (2013)
$2,200,000
How do we proceed with funding?
Spillway Project Schedule
First year of project schedule in months Second year of project schedule in months
Tasks
1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th
Final Design Review by NC Dam Safety *****
FEMA's CLOMR/LOMR Process
Advertisement for Construction Bids
Pre-Bid Meeting with Contractors
Bid Review Period
Contract Award and Notice to Proceed
Construction Period
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*********approx. 10 months *********