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|Title:||Evaluation of techniques to estimate annual water quality loadings to reservoirs|
|Authors:||Environmental and Water Quality Operational Studies (U.S.)|
Westerdahl, Howard E.
Ford, William B.
Lee, Charles R.
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: Five techniques for determining annual water quality loadings were compared and evaluated according to data requirements, advantages and limitations, comparability of results, consistency of application, and technical personnel required. Recommendations were made concerning data collection in the field to characterize water quality loadings, such as suspended solids (SS), total Kjeldahl nitrogen (TKN), and total phosphorus (TP). The techniques evaluated included two regional methods, Midwest Research Institute (MRI) and National Eutrophication Survey (NES). The three instream techniques evaluated were: average flow, average concentration (Q*C); flowweighted concentration (QC); and flow interval (FI). Regional methods required delineation of watershed land use, soil descriptions, and consultation with experts, e.g., U. S. Department of Agriculture-Soil Conservation Service, for coefficient selection. Instream techniques required streamflow and water quality data. The agricultural Sandusky River and Honey Creek watersheds in Ohio and the forested Caddo River watershed in Arkansas were selected as prototypes for comparison of these techniques. Water quality parameters included in the study were SS, TKN, and TP. The results were used as input to a reservoir trophic status assessment procedure to compare their applicability to Corps of Engineers (CE) reservoir planning. As a result of this study, it was concluded that the primary value of the MRI technique was to familiarize the user with the watershed's physiographic features and hydrologic response characteristics to better interpret water quality loading estimates. The NES method has only limited application, at best, to CE projects in selected geographical areas of the United States. The generalized regional methods for the most part were not adequate for estimating annual water quality loadings to reservoirs. Of the three techniques that use available surface water quality and streamflow data, only the FI technique is statistically valid, and it is recommended for estimating annual water quality loadings to reservoirs based on the aforementioned evaluation factors. However, those water quality parameters that may load streams as a function of season and flow would require intensive sampling and analyses to statistically characterize the short-term loadings during the year. The Q*C technique is applicable for water quality constituents that maintain fairly constant concentrations through the range of streamflow. The QC technique requires data representative of the flow range and runoff water quality characteristic of the watershed. Field sampling programs for the purpose of estimating nonpoint source water quality loadings to reservoirs should include simultaneous measurement of flow and water quality to the reservoir. Samples should represent wide ranges of flow at different seasons of the year. Automatic water samplers that are activated by changes in flow velocity or river stage are recommended where extensive sampling is required.
|Appears in Collections:||Technical Report|