RESPEC Tool Helps Communities Manage Flood Events

Watertown, SD—Officials from Brookings and Watertown got a glimpse Friday of a new flood forecasting tool that may help their communities better survive Mother Nature’s occasional onslaughts of water. Flooding in 2011 on the Missouri River caused a major state-driven mobilization to protect property in north Sioux City. Much of that effort was done in the wrong place. So, South Dakota hired RESPEC Engineering of Rapid City to develop a model of the Big Sioux River north of Watertown to its confluence with the Missouri River near Sioux City. Called the Big Sioux River Flood Information Project, the model is nearly complete, and will help direct future flood fights. Because of Watertown’s historic flood problems, RESPEC spent significant time developing a variety of maps for the city.

Local officials will be able to input different scenarios. For example, if Lake Kampeska was a foot below full, as it was in April 1997, forecasters could estimate what would happen if the peak flow was 7,800 cubic feet per second, as it was that year. The model will show emergency officials which areas will be impacted first and later as the flood progresses. It allows officials to add different parameters, such as closing gaps in the dikes on 10th Avenue and Third Avenue. When operational, the model will run continuously, allowing city officials to monitor periods of significant rainfall and predict flood impacts in real time. “Basically, the model tells us that when it rains, how much water is coming, how much it will spread out and how deep it will be,” said Jared Oswald, RESPEC’s manager of watershed management. “This is a tool built to help plan for and manage flood events.”

During the past couple of years, RESPEC has gathered as much information about the Big Sioux River basin as possible. It used stream gauges managed by the U.S. Geological Survey for historical data. It discovered gaps of information and is working with the S.D. Department of Environment and Natural Resources to locate 23 more gauging stations along the basin.The lack of stream gauging was vivid in Brookings. The Big Sioux River does not threaten Brookings. Instead, Six Mile Creek, a tributary to the Big Sioux, is that city’s flood nightmare. But there is no stream gauge above Brookings to warn city officials trouble is imminent. A new gauge will be installed soon because of the modeling effort.

In Watertown, the model reveals what many of us familiar with local flooding already know. Sioux Conifer Road essentially acts as a levy forcing more water into Lake Kampeska than naturally occurs. Conversely, it protects the city from an earlier onslaught of flooding. Once water starts flowing over Sioux Conifer Road, lake levels stop rising and flooding increases through the city. The model also shows that a levy constructed on the Big Sioux’s west side south of Fourth Avenue serves little purpose. If the city desired, the model could show what would happen if that levy were raised.

Another scenario RESPEC programmed into the model is an ice jam at the bridge on U.S. Highway 212. We should hope that never happens as much of the south half of town from our swimming pool to the east side of U.S. Highway 81 would be flooded. Oswald said the model will help officials “in a real-time flood fight” as well as enabling them to be proactive. “Perhaps you can build in some possible defensive measures now,” he said.

Already, Sioux Falls and north Sioux City are using the preliminary model to consider alternatives. The southeastern part of South Dakota faces a double threat from the Missouri and Big Sioux and flooding is never far from mind, as it is in Watertown. Oswald noted that at a recent meeting in north Sioux City it was revealed that the snowpack in the upper Missouri basin is as moisture laden as it was in 2011 and the Oahe Reservoir is fuller. Long range forecasts do not, however, call for the rain that triggered the last flood.

One can only hope Mother Nature agrees.

This article was written by Brad Johnson. The official article can be found here:

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