This research is the first known application into using airborne geophysical methods to evaluate and classify levees. This research is an important step toward developing new technologies and methods to rapidly screen and evaluate earthen flood control levees for safety against flooding. An investigation of airborne geophysical methods was conducted on levees in the lower Rio Grande Valley and involved electromagnetic induction, magnetometer, and LiDAR surveys of the levee system. Airborne EM signatures were analyzed by geologic mapping of floodplain depositional environments, examination of published soils data, and drilling of borings. A geographic information system was developed to manage the various data sets and evaluate historic land use changes and development of the flood control systems to better understand the signatures using airborne methods. This research presents information about the historic basis for evaluating and classifying levees, which is based primarily on the federal perspective and flood control experiences in the lower Mississippi River Valley, where national floodplain engineering methods and standards were developed. This research examines the evolution of today's flood control policy, and the development of engineering assessment procedures, and the application of geophysical methods to provide critical information about levee failure mechanisms and assessment of flood control systems.

This research demonstrates that topographic base maps and Sengpiel sections showing the results of electrical conductivity or resistivity surveys at different frequencies along the levee corridor provide accurate and valuable information to determine the composition of floodplain soils and the foundation stratigraphy to assess modes of levee failure, to aid in the placement of borings to obtain material properties of the levee and foundation, and to determine the extent of levee reaches with similar properties for the engineering analysis. The main purpose for segmenting the levee system is for identifying reaches with similar geotechnical properties for an engineering evaluation and to identify areas where anomalous conditions may occur. Airborne geophysical methods offer added benefits and improvements over traditional engineering methods to evaluate levees based solely on evenly spaced borings along the levee right-of-way, where zones of weakness may be missed. The volume of earth being measured by multiple frequency airborne EM techniques corresponds primarily to the foundation of the levee instead of the body of the levee in smaller levees. Ideally, airborne methods would be supplemented with high resolution ground based EM methods to better define anomalous conditions. Data derived from airborne sur-veys are used in a levee screening process developed during this research to rank levees for the most efficient use of limited maintenance resources and subsequently target reaches for focused studies using traditional engineering methods. Airborne EM surveys show that local variations in electrical conductivity occur, and usually corre-spond to abrupt geologic boundaries in the levee foundation associated with different types of depositional environments (i.e., abandoned channel, abandoned course, point bar, flood basin, crevasse splay, chute, etc.).