Both models start with a soil erosion and water quality packages which use the Universal Soil Loss Equation to predict sediment suspension; the sediment delivery ratio to estimate the actual sediment discharging into the streams; and the potency factor to estimate the pollutants (BOD, COD and SS) flowing into the streams. Afterwards, Model BMP1 estimates costs, performances and evaluates environmental impacts for various cropping management and land treatment practices which include contour, terrace, no-till, rotation and their combinations; and so does the Model BMP2 for various constructional management practices which include diversion, sediment basins and floodeater retarding structures.

Both models were applied in Oklahoma and satisfactory results were acquired. It was found that corn-hay rotation is the BMP for BMP1 application on a watershed in panhandle area and a combination of sediment basin and floodwater retarding structure is the BMP's for BMP2 application on a watershed in central Oklahoma.

This study is to develop two computer models (BMP1 and BMP2) by which a Best Management Practice (BMP) can be selected to control the Non-Point Source Pollution (NPSP) in Oklahoma.

Model BMP1 selects only one BMP from a group of management practices and Model BMP2 selects one or several BMP's as a series on a watershed. BMP1 can be incorporated with BMP2 as a subroutine when both cropping and constructional management practices are considered. Since each of three criteria--cost, performance and environmental impact--may have its own BMP, a ranking method is introduced to provide an objective evaluation on selecting a BMP. Different weights are assigned to these criteria from farmer's and governmental point of view.