|Caldwell, Larry - USDA, NRCS|
Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: October 15, 2000
Publication Date: N/A
Technical Abstract: Since 1948, the USDA-NRCS has constructed over 10,000 upstream flood- control dams in 2000 watersheds in 47 states, over two-thirds of these dams have a design life of 50 years. For many of these dams, the reservoirs are filling with sediment. Before any rehabilitation strategy can be designed and implemented, the sediment impounded by these dams must be assessed in terms of the structure's efficiency to regulate floodwaters and the potential hazard the sediment may pose if reintroduced into the environment. Here we present preliminary results of a demonstration project evaluating technologies for the cost-effective characterization of impounded sediment. For two reservoirs in Oklahoma, geophysical surveys were conducted using a seismic system designed for unconsolidated sediments in shallow water, continuous sediment cores were extracted using a vibracoring system, and chemical analysis of the sediment was performed to assess sediment quality. Seismic profiles of the deeper reservoir show numerous reflectors 0.1 to 0.5 mm thick at subsurface stratigraphy of mud, sand, and gravel that is difficult to correlate with the seismic records, yet sedimentation rates determined using radioactive cesium show consistent trends. Concentrations of heavy metals and agrochemicals within the deposited sediment show values typical of cultivated watersheds. Ongoing work is linking changes in land-use and hydrology with rates of deposition and sediment quality.