University of Iowa Flood Recovery

Challenge

After the 2008 flood events in eastern Iowa, the Federal Emergency Management Agency (FEMA) reevaluated the 100 and 500 year floodplains for the affected area. As a result, the University of Iowa was required to provide additional protection for the Memorial Union Building, which is located within the new 500 year floodplain of the adjacent Iowa River. The university subsequently proposed a flood protection system which would include a two-tiered floodwall constructed along the west side of the existing building. A geotechnical investigation identified a subsurface profile generally consisting of eight to 11 feet of soft to medium stiff clay fill over very soft to medium stiff native clay to approximate depths of 16 to 24 feet below grade. At some of the boring locations, loose to very dense sand was observed below the clay to approximate depths of 44 to 49 feet. The alluvial soils were underlain by weathered limestone bedrock, evident by auger refusal depths from 25 to 49 feet. Groundwater was observed at depths from 12 to 16 feet during drilling, but is expected to fluctuate with the water level of the adjacent river.