Geotechnical evaluation of the Brownsville levee cracking and partial slope failure

Abstract

Abstract : The U.S. International Boundary and Water Commission (IBWC) discovered cracks and a partial slope failure on a newly refurbished levee section and adjacent floodplain along the Rio Grande River in Brownsville, TX. The partial failure followed a significant drop inwater level in early April 2014. A geotechnical investigation was performed by the U.S. Army Engineer Research and Development Center (ERDC) to determine the causes for the partial levee failure and provide remediation alternatives. A series of events, combined with the local geologic conditions, led to the partial slope failure. Events included the 2012 levee construction, fluctuation and rapid drawdown conditions in the Rio Grande, and a higher elevation of Lake Brown (an oxbow of the Rio Grande) relative to the river. Progressive or creep-type failure mode was identified as the probable mechanism to explain the deformation observed in the field, and this was confirmed by seepage and stability analyses. Based on this evaluation, recommendations for remediation include: (1) implementation of a vegetation control program, (2) short-term monitoring, (3) evaluation of other locations along the river with similar river geometry and groundwater conditions, (4) efforts to minimize sudden drawdown, (5) additional analyses using the design hydrograph, and (6) incorporating cost/benefit analyses for the different alternatives.