MODELING THE HYDROCHEMISTRY OF THE CANNONSVILLE WATERSHED WITH GENERALIZED WATERSHED LOADING FUNCTIONS (GWLF)

The Cannonsville Reservoir of the New York City water supply is located approximately 100 mi northwest of the city. The Generalized Watershed Loading Functions (GWLF) model, which is a lumped parameter watershed model that simulates monthly nutrient and sediment loads from nonpoint sources, was applied to the reservoir using recent land-use and stream monitoring data, and several model revisions were then made, and the model was tested again. The revised GWLF model incorporated unsaturated zone leakage, sediment yield timing, urban loading functions, point source particulate nutrients, and seasonal variation in septic system failure rates. All governing numerical equations are provided. Model performance was improved most by revising sediment yield timing, especially in terms of simulated particulate phosphorus and total P, while the addition of unsaturated leakage improved the hydrologic predictions during low-flow months.