May 29th river projections

We received several questions from residents yesterday about the river forecast being off. This is very important to us as we use data to drive decisions and to give guidance to residents. In conversing with the US Geological Survey and National Weather Service yesterday, a lot was learned by us from this week’s severe storms and flooding events. We received the following feedback from National Weather Service in explanation of the projections being off yesterday:
“The river forecast for the Des Moines River at Ottumwa on Wednesday was difficult. We had to consider many factors including runoff from recent rainfall and releases from Red Rock Reservoir upstream. Once it became apparent that the forecast was too high, we edited the forecast in the afternoon and lowered our forecast crest by 0.7 feet.
Another complicating factor in this forecast was the stage/flow relationship for the river at Ottumwa. Our river forecasts deal with flow, which relates to the volume of water in the river. During the afternoon the U.S. Geological Survey performed a flow measurement at Ottumwa and discovered that the relationship was off by nearly a foot. The stage was fine, but how it relates to the flow was off a foot. This discrepancy was one reason why we were having such a hard time forecasting this spot. We were getting more flow for a given stage.”
Necessary corrections were made by USGS. We have high confidence in the products produced by National Weather Service and they are excellent partners that respond to our calls for information. There have been many conversations over the past few days.
So how about the rest of the week? Below are current projections. Red Rock will be increasing outflow this Friday morning from 30,000 to 50,000 cfs. This is projected to bring the river back up on Saturday to approximately 15.5 ft. following a brief dip in level on Friday. You can keep an eye on the river gauge, forecast and outflow projections at www.wapelloready.org/river