Iowa watersheds project: Planning and assessment of flood reduction strategies in agricultural watersheds

摘要

Since European settlement of Iowa, USA, fertile soils and favorable climate have been exploited to create one of the most productive agricultural regions in the world. The majority of Iowa's native prairie, woodland, and wetlands have been replaced by annual corn and soybean crops. Drastic changes in land cover and drainage have altered Iowa's hydrology, generally increasing runoff and flood peaks. Over the past two decades, landscape changes have been coupled with recent increasing trends in frequency and intensity of heavy rainfall to produce several severe floods. Following the devastating 2008 Iowa flood, the US Department of Housing and Urban Development (HUD) provided Iowa funding to investigate basin-scale flood mitigation strategies. The Iowa Flood Center (IFC), a unit of the University of Iowa's IIHRHydroscience & Engineering, is leading the effort to evaluate methods of increasing soil water holding capacity, reducing soil erosion, and managing upland runoff under saturated soil moisture conditions. Large-scale hydrologic simulations were developed for five Iowa watersheds ranging in area from 1400 km~2 to 4400 km~2 and representing Iowa's variability in topography, soils, and land use. Large-scale simulation results were used to identify regions with high runoff potential, where mitigation will provide the mòst benefit. IFC is coordinating with local resource management agencies to construct pilot mitigation projects and monitor their performance. Smaller-scale hydrologic simulations, including more detailed representation of physical processes, are being developed for areas selected for pilot mitigation measures. Based upon monitoring data,numerical models will be used to predict potential cumulative benefits of numerous similar projects distributed throughout a watershed. Project results will provide guidance for effectively implementing distributed flood mitigation strategies to provide cumulative benefit for downstream communities.