Establishing A Flood Relief Center in Pahrump, Nevada

BACKGROUND

The Federal Emergency Management Agency (FEMA) defines flooding as: a general and temporary condition of partial or complete inundation of normally dry land areas from: (1) The overflow of inland or tidal waters; (2) The unusual and rapid accumulation or runoff of surface waters from any source; (3) Mudslides.

Flooding is the most frequent and costly natural disaster according to the American Red Cross. The subsequent damage can cause power outages, disrupt transportation, damage buildings, and create landslides. It is therefore important that an adequate location be chosen for a disaster relief site well in advance of an actual flood to ensure resources are available and provided to all those affected.

Nevada receives relatively high rainfall and therefore is at-risk for floods and flash floods. The state has experienced a number of costly floods, such as the 1999 Las Vegas Flash Flood.

Figure 1 displays the monthly normal precipitation values for Nevada in December. The map was generated using inverse distance weighted interpolation (IDW) with a power of 2, meaning that distance (proximity to weather stations with precipitation data) was given little weight in determining the precipitation values of areas without available data from NOAA. Figure 1's results had a mean error value of 0.00126.

Figure 1. Map of normal precipitation values for the month of December in Nevada.

Out of the entire state of Nevada, Pahrump is a town with particularly high flood risk (it receives 3.76 inches of rain in December on average). For this reason, this report focuses on the town for analysis of a suitable location for a flood relief center.

Pahrump and the rest of Nye County lie east of Death Valley and west of Las Vegas. Pahrump has experienced a population increase in its floodplain by 54.6%. There are not many natural bodies of nearby, but flash flooding in arroyos puts residents there in danger. In 2010, the county had roughly 9,300 homes in FEMA floodplains. By 2016, it had nearly 14,400.

To determine a suitable location for a flood disaster relief site, the following criteria was considered:

terrain slope
elevation
proximity to roads (within 2 miles)
relation to fault lines (avoid locations above a fault line)

Figure 2. Site suitability map of proposed locations for a disaster relief center in the event of a flood in Pahrump, Nevada.

The following values were used to reclassify the elevation and slope of the USGS raster file:

Elevation:0-250m: 0 points250-500m: 1 points500-750m: 2 points750-1000m: 3 points 1000-1250m: 4 points1250-1500m: 5 points1500-2000m: 6 points2000-3618m: NO DATA
Terrain slope:0 -1 degrees: 5 points (most desirable)1 - 3 degrees: 4 points3 - 5 degrees: 3 points5 - 10 degrees: 1 pointAbove 10 degrees: 0 points

For elevation, elevations and their corresponding number of points are positively correlated because higher elevations were prioritized because they are further out of the flood zone. However, slopes exceeding 2000m received no points because it would be inefficient to build a relief center at such high elevations. For slope, the lower the number of degrees, the higher the number of points it received. Under ideal circumstances, the relief center would be built on terrain with a slope ranging from 1 to 0 degrees. The raster calculator tool was used to first add the values of the reclassified slope and elevation raster layers, and then filter through all existing scores to only display those of 9 or above (using the equation: ("score.tif">=9)*"score.tif").

To ensure that suitable sites were at least within 2 miles of an existing road, a buffer with a 2 mile radius was applied to all regions earning a score of 9 or above. In addition, a buffer was applied to the shapefile of fault lines so as to prevent all suitable sites from being located on a fault line. Therefore, maximizing the safety of the location selected (in the event of an earthquake).

Figure 3. 3D visualization model of a suitable flood relief center in Pahrump (see legend from Figure 2). Red lines represent fault lines and gray lines represent roads.

ANALYSIS

Most sites do not meet all 4 desired criteria (11 is an ideal, however rather unrealistic score). The most feasible places to establish a relief center are zones with scores of 9 that overlap those with a score of 10.

Further analysis should focus on additional factors such as population density. While elevation, slope, and proximity to roads and fault lines are all important factors that must be met, to maximize the number of people the center is able to serve it would be ideal to choose a location where population is most heavily concentrated. Other factors could include: proximity to utilities and supermarkets (where bulk items could be found to replenish the center).

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SOURCES

https://www.cheatsheet.com/culture/american-cities-homes-danger-flooding.html/https://earthquake.usgs.gov/hazards/qfaults/https://www.nevadadot.com/doing-business/about-ndot/ndot-divisions/engineering/location/geospatial-datahttps://www.ncdc.noaa.gov/cdo-webhttps://earthexplorer.usgs.gov/https://www.arcgis.com/home/item.html?id=f7f805eb65eb4ab787a0a3e1116ca7e5

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