SGER/Collaborative Research: 2008 Midwest Levee Failure Invesigation

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This Small Grant for Experimental Research (SGER) award is an immediate field reconnaissance and data collection effort to collect sensitive and time-dependent perishable levee performance (failures and successes) data, documenting the performance of the flood protection levees along the Mississippi River between Davenport Iowa and St. Louis Missouri during the June and July 2008 storms. The objective of the study is to perform an integrated evaluation of levee performance subject to "extreme" loading, such as extended duration elevated river stages (inducing underseepage/internal erosion) and overtopping/scour erosion. Individual erosion characteristics for levee performance have been studied and significantly advanced in the last ten years, but no integrated studies have been performed that synthesize all the erosion characteristics in one model. This study provides desperately needed comprehensive field data to validate empirical formulas and numerical models that have been developed to analyze erosion of levees. There are lessons of potentially vital importance to be learned from the performance of the Midwest levee systems. The data collection consists of detailed laser imaging surveys (Terrestrial LiDAR) of the breach and erosion/scour features, characterization of the vegetative grass cover, characterization of the levee soil materials (Unified Soil Classification System, Atterberg Limits, density, grain-size distribution, and Erosion Function Apparatus rating), documentation of river stage at the location of levee failures from eyewitness accounts as well as river stage gaging stations, and lessons from the engineers and personnel who observed the levee failures and performed/oversaw repairs. Thus, this study provides comprehensive field data for use in advancement of levee erosion-resistance design. There are thousands of miles of earthen levees in the United States, many without any engineering design or certification, that are supposed to provide flood protection for residents living within the protected zone behind the levees. Of the levees that were designed in accordance with accepted engineering methods, very few of the levees have been designed to resist the most common failure type, overtopping. Thus, the results of this field reconnaissance study can be directly applied to the entire U.S. flood protection system to evaluate the reliability of earthen levees as flood protection elements, as well as recommendations for levee improvements to increase performance reliability.