State officials are preparing for the impact of increased water flow on the Missouri River from the Gavins Point Dam in South Dakota. Emergency Management and Homeland Security director, Derek Hill, says the increase is expected to raise the water level in Sioux City another one half to one foot, while in Council Bluffs and points south, it will go up only inches.
Hill says they do expect other impacts from the rise in water. He says the increase flow will create more backup in the tributaries, as there has already been some backup. Hill says it is particularly a concern if there is more rain. Hill says the increase flow also increases the pressure on, and water flow around structures that they are already monitoring.
Hill says the most obvious concern are the levees as the increased flow and pressure could cause boils to form. He says they will continue with patrols looking boils on the levee. Hill says that’s not the only concern. Hill says they are also watching to see how the increased flow impacts the embankments against the bridges and the culverts and the roads that have gone under water. Hill was asked which tributaries that flow west cause the most concern.
He says “basically all of them” as he says the Nishnabotna floods periodically anyway and it backs up for several miles, the Floyd River, the Big Sioux and Perry Creek which flows into Sioux City. Hill says residents around those rivers should be prepared for possible flooding.
Hill says their advice for people on the tributaries or areas that could be inundated with heavy rain, is they should be prepared for flooding. He says people living near levees should also be alert to the changing conditions. The Fremont County emergency manager ordered mandatory evacuations Wednesday for resident who live west of Interstate 29. Hill says that’s a precaution mainly because the levee there is new.
Hill says the dirt was settled the best it could be, but he says it has not like an older levee where the earth as had the opportunity to naturally compact. Hill says they are monitoring all the levees in the area and do not have a particular concern about one over the other.
Hill says the impact of the increased Gavins Point output will be less downstream of Sioux City as the water has gone down some there and that will be offset by the increase flow. Hill made his comments during an update Wednesday afternoon.