Flood Inundation Mapping on the St. Marys River in Camden County

Flood Inundation Mapping
on the St. Marys River in
Camden County, Georgia
from Tropical Storm Debby
July 2012
Presenter - Paul Speich CFM, GISP
GIS Manager
City of Kingsland, Georgia
[email protected]
912-729-8222
From June 22-27 Tropical Storm Debby
impacted the South Georgia-North Florida region
with record rainfall and flooding. The City of
Kingsland GIS Department took the opportunity
to document the extent of the riverine flood water
inundation along the St. Marys River in Georgia
as a baseline for use in future DFIRM updates, as
well a tool in evaluating the accuracy of the extent
of current regulatory flood data for the area.
Over the course of the event, high water marks
were recorded at public access points along the river
up to cresting. The resulting high-high water marks
were GPSed and compared to newly generated
LIDAR contours for the county. With this data, a
new spatial extent of flooding was generated using
the Arc GIS program. This new extent was
compared
to
the
current
DFIRM
data
differences between the two were formulated.
.
and
Results of the exercise showed this event to be a new
record high water event, surpassing previous record
flooding from hurricane Dora in 1964, and that the
current regulatory data for the area is, for the most part,
spatially accurate for a riverine event of this type. Only
Minor modifications to the existing DFIRM as a result of
this event would be needed to match the actual recorded
inundation extent. The new flood data was forwarded to
the FEMA CTP (cooperating technical partner) for
inclusion in the updated flood maps due out in 20132015.
St. Marys River HUC
10 Basin
Georgia
Florida
Storm track passes directly over the St. Marys basin
3” – 5” of rainfall throughout the Basin
Storm track passes south of the St. Marys basin
10” – 25” of rainfall throughout the Basin
USGS Stream gage at
MacClenny, FL. Approximately
60 river miles upstream from
Camden Co. Ga.
High Water Sample Sites
Tropical Storm Debby inundation area
Sample LIDAR generated 2’ contours
Springhill sample area Digital Elevation Model
Springhill sample area inundation
DFIRM Overlay of inundation extent in Springhill
Current study area DFIRM data
Areas inundated, but excluded from the current DFIRM data (under
reported)
Areas included in the current DFIRM data, but not inundated
(over reported).
Summary Table
Summary
• Record Landmark events.
Photos, data, interviews
• Use the most up to date
LiDAR and air photo data.
• Have detailed studies done.
• Protect the floodplain.
Future Actions
•Analysis of affected properties for
substantial damage, repetitive loss.
•Review of building elevation codes and floodplain
management practices for the area.
•Development of a prevention/mitigation plan.
Data Sources; National Weather Service, USGS,
State of Georgia, Nassau County Florida, Camden
County Georgia, City of Kingsland Georgia.
Contact Information
Paul Speich CFM, GISP
City of Kingsland
PO Box 250
Kingsland, Georgia 31548
912-729-8222
[email protected]