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.

2

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.

3

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?

4

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.

5

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.

6

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 Color Number of Roads 1 Yellow 103 2 Light Orange 444 3 Dark Orange 745 4 Light Red 1154 5 Dark Red 1441

*The number of roads for Category's 2 through 5 include each of the previous category's roads

7

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.

8

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://georgewbush-whitehouse.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.