STORM SURGE AND EVACUATION ROUTES:
DOG RIVER WATERSHED
Sarah Hill
Hurricanes and storm surges are not an uncommon occurrence along the Gulf
coast. Knowing in which areas flooding will occur will better prepare residents of the
Dog River Watershed during a hurricane. The purpose of this paper is to show the areas
affected by multiple category storm surges and evacuation routes best taken if leaving
under flooded conditions. Research will be conducted using elevation models created
from ArcGIS along with road patterns and average storm surge heights for each category
hurricane. Using these models and maps, I will be able to determine where storm surge
reaches and which roads are best fit for evacuation routes.
Keyword: storm surge, elevation models, evacuation
Introduction
Hurricanes are not uncommon for people living on the Gulf coast. On average,
Alabama’s coast is hit once every 7.5 years by a hurricane, and hit about once every 1.5
years by tropical storms (Chaney, 2012). “Storm surge, one of the most damaging
components of a hurricane, is a massive dome of water often 50 miles wide that sweeps
across the coast near the area where the eye of the hurricane makes landfall” (Jewell,
2012). “Prior to the mid to late 1960s storm surge flooding was the major cause of
hurricane-related deaths but has accounted for only about six percent of all hurricane
deaths from 1970 through 2002…However, storm surge is still a potential killer and is a
primary reason coastal areas are evacuated when they are threatened by hurricanes”
(Storm Surge, 2005). During Hurricane Katrina in 2004, New Orleans was unprepared
for the storm surge that hit. Rescues were delayed leaving victims stranded, roads to
evacuation safe houses were cut off, and supply routes were completely flooded. As a
result, over 1,800 citizens of New Orleans died (The White House, 2005). Educating the
public will prevent casualties due to the lack of understanding the threat of a storm surge.
Parts of the Dog River Watershed are affected by all category storm surges
(Figure 1). The areas affected are within the eastern side of the watershed. The western
half of the watershed is more elevated and therefore less affected by storm surge.
The purpose of this paper is to educate the public through use of geographic
information systems (GIS) about multiple category storm surge potential and to show
which roads will be partially or completely flooded during a storm surge event. Provided
will be detailed road maps showing evacuation routes to be taken when the storm surge
hits. Mapping the roads that will be partially or completely flooded during a storm surge
event will be very beneficial not only for those evacuating to higher areas but also to land
rescue crews answering emergency calls from stranded victims.
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Figure 1 shows the extent of category's 1 through 5 hurricane storm surge.
Research Question
The Dog River Watershed, as shown in Figure 1, is affected by storm surges of
each category hurricane. Which roads will be flooded, either partially or completely?
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Methods
The methods I used to complete my research are explained below. I first created a
map to determine where the storm surge would reach within the Dog River Watershed
(Fig 1). The data used was collected from the City of Mobile’s GIS database. After
determining where the threat of storm surge occurred, I needed elevation data in order to
determine which roads would be flooded. The elevation data, in the form of DEMs, were
collected from the US Department of Agriculture Geospatial Data website. I then created
through ArcGIS 9.3 hillshade and contour models to better display the elevation data (Fig
2&3). Since each road line segment has a range of elevations because of changes in the
topography, I judged each road segment by its minimum elevation. This showed me the
minimum height that each road had to be in order to escape flooding. To get these
minimum road elevations, I had to create an integer raster from the contour layer. After
obtaining that, I spatially joined it to the roads layer, joining each road segment elevation
with its appropriate road. I then took the elevations of the roads and compared them to
the elevation of the Dog River surge heights provided by the Army Corps of Engineers.
This comparison determined which roads would be completely or partially flooded in the
event of a storm.
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Figure 2 displays the elevation of the Dog River Watershed through a hillshade model.
The lighter colors show higher elevations while the darker show lower elevations.
Figure 3 displays a contour map of the Dog River Watershed. Each contour line
represents two meters.
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Results
My results are displayed in Table 1 and Figure 4. Using the minimum elevations
of the road segments and the elevation of the area, I was able to determine which roads
would be partially or completely flooded in any category storm surge. There are 103
roads that will affected by a Category 1 storm surge; 444 will be affected by a Category
2; 745 will be affected by a Category 3; 1,154 will be affected by a Category 4; and
1,1441 will be affected by a Category 5 storm surge.In the map below, yellow is used to
show which roads will be partially to completely flooded in a Category 1 hurricane; light
orange is used to display which would be affected by a Category 2; dark orange is used to
show which would be affected by a Category 3; light red is used to display, which would
be affected by a Category 4; and red shows which would be affected by a Category 5.
Table 1 shows the number of roads within the Dog River Watershed that will be partially
or completely flooded by storm surge
Partially or Completely Flooded Roads within the Dog River Watershed
Category
1
2
3
4
5
Color
Yellow
Light Orange
Dark Orange
Light Red
Dark Red
Number of Roads
103
444
745
1154
1441
*The number of roads for Category's 2 through 5 include each of the previous
category's roads
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Figure 4 is a map showing which roads will be partially or completely flooded in a storm
surge. Note that the roads for Category’s 2 through 5 will also include the previous
category’s roads.
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Conclusion
My project concludes that there are areas within the Dog River Watershed that are
affected by all category hurricane storm surges. As a result, there are also many roads
within the Watershed that are affected by all category hurricane storm surges. Through
the use of GIS, I was able to determine the elevations of these roads and map out which
were not to be used in the event of a hurricane due to being completely or partially
flooded (Figure 4). This research can be used as education tool for the citizens of the
Dog River Watershed as well as for rescue crews answering emergency calls. Knowing
the storm surge potential in their area and which roads are safe to travel during flooded
conditions will allow for last minute evacuations to higher ground and easier and more
efficient rescue missions from emergency personnel.
References Cited
Chaney, Philip L. "Climate." Encyclopedia of Alabama. Accessed March 2, 2012.
http://encyclopediaofalabama.org/face/Article.jsp?id=h-1283.
Jewell, Beth. "Storm Surge: NOAA Hurricane Education." National Oceanic and
Atmospheric Association. Accessed March 2, 2012.
http://www.climate.noaa.gov/education/hurricanes/stormsurge.pdf.
Storm Surge: A “Rising” Concern Among Coastal Residents [online]. (2005) [Accessed
March 22, 2012]. Available from:
http://www.magazine.noaa.gov/stories/mag178.htm.
The White House. (2005). “Chapter four: A week of crisis (august 29 - september 5)”.
Retrieved from website: http://georgewbushwhitehouse.archives.gov/reports/katrina-lessons-learned/chapter4.html
US Army Corps of Engineers. "Mobile County 1999 Hurricane Surge Map." Accessed
March 2, 2012.
http://www.sam.usace.army.mil/stormmap/images/MsurgeSML.jpg.
US Army Corps of Engineers. “Mobile County, Alabama Hurricane Surge Atlas
Introduction.” Accessed April 20, 2012.
http://chps.sam.usace.army.mil/ushesdata/alabama/AL_PDFs/mobileintropage.
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