Fréchet Distribution and Water Quality Management

For design projects in the water quality management area, it is a fundament requirement to accurately determine the exact amounts of dissolved contaminants in different types of waters for remedial measures in order to enhance the water quality for best management practices. In open channel flow, the division of total weight of dissolved contaminants, as attributed to direct runoff and baseflow, is generally carried out in an approximate manner based on experience and engineering judgment. To accomplish the same objectives with added economic benefits, accuracy, and a faster processing speed, a methodology comprising the two-parameter Fréchet Distribution is presented. A large sample of contaminantgraphs from different geographical areas of the 48 contiguous States is considered in this investigation. The two parameters of the Fréchet Distribution are related to the dimensionless shape parameter and the storage time constant of the given drainage basin, respectively. Both parameters are determined through the analysis of the measured contaminant-load data. The calibrated form of the two-parameter Fréchet Distribution describes the natural contaminantgraph curve well and furnishes speedy and accurate estimates of the respective portions of contaminant load being carried by the direct runoff and baseflow.