Statistical Evaluation of BMP Effectiveness in Reducing Sediment Impairment in Mermentau River Basin

This paper presents a statistical method for the evaluation of effectiveness of Best Management Practice (BMP) in reducing sediment impairment using water quality data monitored from 1980 – 2006 in the Mermentau River Basin. The statistical method mainly involves (1) determination of seasonal variations in the mean of flow and water quality parameters in order to identify critical months and main sources of water pollution, (2) detection of time-variation trend of water quality in different watersheds within the basin in terms of the mean and standard deviation of TSS and turbidity, and (3) evaluation of the effectiveness of BMPs in improving water quality based on the trend analysis and water quality criteria. Results of the statistical evaluation show that (1) April and February are the two critical months of the worst water quality in terms of TSS and Turbidity; (2) The main pollution source in February is soil/sediment erosion caused by wet weather runoff and high river flow; (3) The severe pollution in April is mainly caused by releases of muddy rice_field water but wet weather runoff makes the water quality even worse; (4) Since the implementation of BMPs, water quality in the Mermentau River Basin has shown some improvements in terms of TSS and turbidity. However, most watersheds in the basin have not yet met water quality standards. The most polluted areas in the basin are the two watersheds Bayou Queue de Tortue and Bayou Nezpique, followed by the watersheds Bayou Plaquemine Brule and Bayou Lacassine; (5) BMPs need to be enhanced in the basin to meet water quality standards.