Assessing sedimentation issues within aging flood-control reservoirs

Flood-control reservoirs designed and built by federal agencies have been extremely effective in reducing the ravages of floods nationwide. Yet some structures are being removed for a variety of reasons, while others are aging rapidly and require either rehabilitation or decommissioning. The focus of the paper is to summarize collaborative research activities to assess sedimentation issues within aging flood-control reservoirs and to provide guidance on such tools and technologies. Ten flood-control reservoirs located in Oklahoma, Mississippi, and Wisconsin have been examined using vibracoring, stratigraphic, geochronologic, geophysical, chemical, and geochemical techniques and analyses. These techniques and analyses facilitated: (1) the demarcation of the pre-reservoir sediment horizon within the deposited reservoir sediment, (2) definition of the textural and stratigraphic characteristics of the sediment over time and space, (3) the accurate determination of the remaining reservoir storage capacity, (4) the quantification of sediment quality with respect to agrichemicals and environmentally important trace elements over both time and space, and (5) the determination of geochemical conditions within the deposited sediment and the potential mobility of associated elements. The techniques employed and discussed here have proven to be successful in the assessment of sediment deposited within aging floodcontrol reservoirs, and it is envisioned that these same approaches could be adopted by federal agencies as part of their national reservoir management programs.