Easing the Sediment Load

Agricultural Research Service scientists in Oxford, Miss., have devised a new method for evaluating streams and rivers impaired by sediment.

Hydraulic engineer Roger A. Kuhnle and geologist Andrew Simon at the ARS National Sedimentation Laboratory are focusing on streams with clean sediments free of chemical contaminants. The two are developing numeric targets for maximum sediment for streams in different regions, since the amount of sediment a stream can handle varies greatly in different parts of the country.

The research involves analyzing and compiling previously collected waterflow and sediment data, along with field data on the stability of a given stream. Kuhnle and Simon will then develop target values for clean sediment that correspond to unimpaired streams in other regions.

All streams and rivers have the ability to handle a certain load of sediment without being damaged, but the difficulty is in estimating that load. Bodies of water that receive too much sediment potentially require a Total Maximum Daily Load (TMDL) assessment.

A TMDL is the level of pollution a body of water can tolerate and still meet water quality standards set by the states, territories and tribes. It also identifies both appropriate uses for each water body--as, for example, drinking water supply, contact recreation such as swimming, or aquatic life support--and the scientific criteria to support such use. Section 303 of the Clean Water Act establishes the water quality standards and TMDL programs.

Eventually, the new procedure will help identify streams especially vulnerable to sedimentation. It should also make it possible to relate the target values for clean- sediment TMDLs to designated uses of the streams and rivers in different regions.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.