Iowa watershed project: coupled surface-subsurface hydrologic modeling to assess distributed flood mitigation practices

Nicholas Thomas, Larry Weber, Keith Schilling

Thursday 2 july 2015

11:15 - 11:30h at Oceania Foyer (level 0)

Themes: (T) Water resources and hydro informatics (WRHI), (ST) Surface and subsurface flow interactions

Parallel session: 11L. Water resources - Flow interactions

Significant rainfall in the summer of 2008 and subsequent flooding in eastern Iowa, USA induced billions of dollars in damage to communities, land, and agriculture. Post flood, the Iowa State Department of Housing and Urban Development allocated $8.8 million to the Iowa Flood Center to plan, implement, and evaluate watershed projects to lessen the severity and frequency of flooding in Iowa. A two phased approach was applied to investigate how diverse basins respond to varying input rainfall and the overall flood hydrology at the basin scale (4,000 km2), and the impact of a specific distribution of flood mitigation practices at the sub catchment scale (45 km2). This paper focuses on the construction, calibration, and validation of a coupled surface subsurface hydrologic model to understand the local effects of distributed projects. In 2014 stream stage sensors, soil moisture and scientific rain gage platforms, shallow groundwater wells, and water quality sensors were distributed throughout a small scale watershed. A combination of simplified calibration techniques along with watershed scale validation to measured data offers confidence in the models capability to reproduce watershed dynamics. Incorporation of build practices through this funding source, along with potential distributions of various flood mitigation strategies are quantified. Extrapolation from the small scale distribution of projects offers insight into the capability of larger basins to mitigate devastating flood events.