Geologic hazards of the Bighorn River Floodplain

This installment continues the series of articles that propose possible solutions to dealing with the geologic hazards of the Bighorn River Floodplain. The following is primarily focused on low-level flooding of several feet above flood stage with damage more or less confined to the floodplain. The limits of the floodplain, upon which most of Thermopolis is situated, are obvious. Stand on Broadway and look west. The west edge of the floodplain is right at Eighth Street where the street begins the climb up to the plateau west of town. The east edge of the floodplain is past the hospital and senior apartments where Warm Springs Road climbs the hill to oilfields on the Thermopolis Anticline. In the future, I will provide a detailed map of the limits of the Bighorn River floodplain as it relates to Thermopolis.

If your home is located on this floodplain, or within about 15 feet elevation above it, get flood insurance. Once the spillway at Boysen Dam is active, the dam can no longer provide flood control but must instead save itself by allowing all excess water to be released. In my article about the “Perfect Storm,” such a scenario is described. Your normal homeowner’s insurance policy does not cover flood damage. The entire floodplain is at risk for flooding.

With regard to mitigating flood damage, we are dealing here with flood crests of up to several feet above flood stage causing flooding due to events such as ice jams and intense rain storms or mountain snow melts during active dam spillway periods. Individual home owners can build low dike systems into their landscaping designs. Any home on the floodplain should be prepared for basement flooding and have a means to reduce first floor incursion of flood waters.

Consider that Greybull has built a levee system to help protect their town from low-level flooding and that we have not. We could protect a considerable area of our town by taking advantage of the railroad grade as a levee. The tracks are at a constant elevation above the floodplain and run along the west side of the river. A dike could be engineered connecting the railroad grade from where it crosses the river (near the Pizza Hut) to the cliff at the former site of the Feed Bag restaurant. The underpass on Park Street would need to have a hydraulically lowered flood gate similar to the tsunami gates in Japan. There are pros and cons to this idea. What do you think? The next installment will address catastrophic flooding events.