Exploring Flood and Drought Data of the Watershed

Using the Advanced Hydrologic Prediction Service from the National Weather Service anyone can look at various information pertaining to a watershed.

The Fourmile Creek Watershed has 7 gauges available to explore (Figure 1)

(All images from https://water.weather.gov/ahps/). 

The symbology of the gauges within the stream indicate:

    6 of the 7 gauges do not have forecasts or probability data available
    5 of the 7 gauges do not have a defined flood category
    1 of the 7 gauges does not have current data available.

Figure 1. Stream gauges within the Fourmile Creek Watershed

Figure 2. Fourmile Creek at Easton Blvd. detailed flood stage information

In Figure 2, a Flood Stage Level of 12.5 feet. Upon double clicking the stream gauge, the image is enlarged and I am given numerous other features to explore. This stream gauge status is updated by past precipitation data as well as forecasted precipitation within 24 hours. I was also able to find more information about multiple flood stage levels (Figure 3).

Figure 3. Scale to Flood categories at Easton Blvd. in the Fourmile Creek Watershed

In 2018, this stream crested at 17.51 feet, the highest on record for this location. There is an option to turn on a FEMA flood layer (Figure 4). When I change the basemap, you can see how the flood plain overlaps with residential neighbhorhoods. Taking this one step further, I looked at the next upstream gauge. While this gauge doesn't have up-to-date forecast data, it's important to note that many agricultural lands are within the floodplain. As such, Polk County Conservation has begun purchasing land from homeowners (both residential and agricultural lands) to restore flood plains and stream channels to their natural channels. One of the main considerations for purchasing lands is to increase storm water management efforts, reducing the effects of erosion and flood waters.

Figure 4. FEMA National Flood Hazard Layer

Figure 5. FEMA National Flood Hazard Layer with Satellite Imagery Basemap

As I stated above, flooding in Fourmile Creek reached an all time high in 2018. During this period, a major flash flood event occurred as a result of thunderstorms stalling out over central Iowa, resulting in 5-10 inches of rain, streams flooding over their banks, and record water levels in both Fourmile Creek and Walnut Creek. A follow-up post will go over this event in depth.