FLUVIAL GEOMORPHOLOGY APPLIED: LEVEE SAFETY AND FLOODPLAIN MANAGEMENT

An estimated 48,000 to 161,000 km of levees line U.S. rivers, with levees being the principal structural flood-protection tool in the U.S. and worldwide. The 2005 Katrina disaster in New Orleans focused attention on gaps in current levee knowledge. “[T]he nation lacks data and information about the physical location of its levees, their ages and conditions, the level of protection each provides, whether levee failure warning and evacuation plans exist and are exercised, who owns and maintains a specific levee system, and the adequacy of the operation and maintenance plan, exercises, and implementation” (ASFPM, 2007). Fluvial geomorphology provides a broad range of data sets and analytical tools for addressing some of these information gaps.

Fluvial geomorphic and hydrologic research in our group uses empirical data to test assumptions and model-based conclusions regarding levee effects. In one project, a 1998 levee-crest elevation survey was precisely re-surveyed for 328 km of levees south of St. Louis. In the intervening ~10 years, local subsidence of up to 1.26 m was documented as well as permitted and unpermitted elevation increases of up to 1.49 m. Other research has focused on levee effects upon river flow dynamics and flood elevations. “That levees increase flood levels is subject to little disagreement” (GAO, 1995); there is, however, wide disagreement over the magnitudes of these increases. By identifying well documented past levee construction projects close to long-duration USGS river gages, we have documented levee-related flood increases (up to 2.3 m), as well as spatial patterns and details of such increases. These empirical results are being used to verify and constrain hydraulic model-based estimates of flood flow conditions and levee effects upon flow conveyance and storage.

Current and future efforts are focusing upon assessing flood risk and efforts to mitigate such risk. By wedding calibrated hydraulic modeling (e.g., HEC-RAS) with flood-risk assessment (using HAZUS-MH and detailed local infrastructure data), the SIU group has been quantifying floodplain exposure as a tool for flood-risk mitigation and testing a range of mitigation scenarios such as property and community buyouts, levee setbacks, and alternative river and floodplain management strategies.