SGER/Collaborative Research: 2008 Midwest Levee Failure Invesigation

这项实验研究小额赠款（SGER）是一项即时现场侦察和数据收集工作，旨在收集敏感的和随时间变化的易损坏堤坝性能（失败和成功）数据，记录2008年6月和7月风暴期间爱荷华州达文波特和密苏里州圣路易斯之间的密西西比河防洪堤坝的性能。这项研究的目的是对堤防在“极端”荷载下的表现进行综合评估，例如长时间河段升高（引起下渗/内部侵蚀）和漫顶/冲刷侵蚀。近十年来，人们对堤防性能的个别侵蚀特征进行了研究，并取得了显著进展，但尚未进行将所有侵蚀特征综合到一个模型中的综合研究。这项研究提供了迫切需要的综合现场数据，以验证已经开发出来的分析堤坝侵蚀的经验公式和数值模型。从中西部堤坝系统的表现中可以学到一些可能至关重要的教训。数据收集包括对决口和侵蚀/冲刷特征的详细激光成像调查（陆地激光雷达），植被覆盖的表征，堤坝土壤材料的表征（统一土壤分类系统，阿特贝格极限，密度，粒度分布和侵蚀功能仪器评级），从目击者的叙述中记录堤坝损坏位置的河段，以及河段测量站。以及那些观察堤坝故障并执行/监督维修的工程师和人员的经验教训。因此，本研究为推进堤防侵蚀设计提供了全面的现场数据。美国有数千英里长的土制堤坝，其中许多没有任何工程设计或认证，它们本应为生活在堤坝后面保护区内的居民提供防洪保护。在按照公认的工程方法设计的堤坝中，很少有堤坝被设计成能够抵御最常见的破坏类型——漫顶。因此，本实地勘察研究结果可直接应用于整个美国防洪系统，以评估土质堤防作为防洪要素的可靠性，并提出堤防改进建议以提高性能可靠性。

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.