Following the 2008 Midwest flood, the U.S. Army Corps of Engineers, Rock Island District, requested funding for a study to improve our understanding of flooding on the Des Moines River at and below the Corps’ Saylorville Lake and Lake Red Rock reservoirs. The study included a scientific assessment of historical stream gage records to estimate the frequency and magnitude of future reservoir outflows and downstream river flows. This study effort helps to better identify and communicate the probability, or chance, of flood events; and assists in the planning and design of future flood-risk-management projects. This study has been titled the Des Moines River Regulated Flow Frequency Study.
In recent decades, the Des Moines River has risen higher and more often prompting the Corps to re-evaluate flow frequency estimates. This study sought to improve the characterization of flood risks on the Des Moines River including an update of reservoir pool-frequency relationships and the flood-flow frequency values downstream of Corps reservoirs. Flow frequency estimates were developed at river gage locations on the Des Moines River from Saylorville Reservoir to Keosauqua, Iowa.
The study involved an extensive review of historic river gage data, reservoir inflows and outflows, and river flow data for a period of record from 1917-2008. Data from the 2010 flood event was not included as the study was well underway prior to the event and it would not have been timely to incorporate the new data. The most recent update of flow frequency values, prior to this study, was made after the 1993 flood using data through 1994.