US Army Corps of Engineers
Rock Island District

Nonstructural Iowa Bridge Sensor Rating Curve Demonstration Project Phase I & II

Iowa's severe flooding in 2008 demonstrated the need for more extensive monitoring of the state's rivers and streams in real time. To address this, the Iowa Flood Center (IFC) developed and maintains a statewide network of stream stage sensors deployed at bridges designed to measure water surface height. Stage data is transmitted automatically and frequently to the IFC for viewing in real time via the Iowa Flood Information System (IFIS). 

The IFC maintains a network of 250 stream stage sensors across the state. Support for sensor deployment has come from the Iowa Department of Natural Resources and the Iowa Department of Transportation. 

The Nonstructural Iowa Bridge Sensor Rating Curve Demonstration Phase I and Phase II projects leverage the existing IFC bridge sensor network data to demonstrate the need for rating curve development at sensor locations. Study partners including the U.S. Army Corps of Engineers, the Iowa Flood Center, the National Weather Service, the U.S. Geological Survey, the Iowa Department of Natural Resources and the Homeland Security and Emergency Management Department have prioritized state-wide rating curve needs and are developing a standard procedure for rating curve data collection by leveraging available data (state Light Detection and Ranging (LIDAR) data, bridge plans, channel cross-section survey data, etc.). Co-located bridge sensor and U.S. Geological Survey gage rating curves are being compared to assess the accuracy of the bridge sensor rating curves.

The implementation of the bridge sensor rating curve methodology utilizing the step-backwater method is a suitable resource of flow data to supplement established USGS stream gage data at locations that do not currently have a USGS stream gage.  The methodology and products are not intended to replace established stream gage data.  However, the products do provide water level and flow information at locations that are currently not served by the USGS gaging systems.  Counties and communities using the IFIS web site and products accept the limitations to the accuracy of the information provided by IFIS.  Counties and communities using the bridge sensor rating curve methodology would need to be aware that the channel cross-section geometry will need to be periodically verified.  The online availability of this data, where no other data is available, allows flood response teams to use their limited time and resources in a more efficient and effective manner rather than engaging in repetitive, time-consuming field reconnaissance in anticipation of an impending high water flood event.

The Executive Summary Report and the Detailed Study Report with Appendices study products are available for flood preparedness planning.