Multi-Scenario Simulation Analysis in prioritizing management options for an impacted watershed system

Waco Lake (Texas, U.S.A.) is a municipal water supply fed by largely agricultural watersheds and is characterized by poor water quality because of elevated nutrient concentrations. Watershed modeling is used to prioritize management options to reduce nutrient loading into the reservoir. A natural (pre-agricultural) system sce-nario of the dominant watershed resulted in 80% reduction of total phosphorus and 74% reduction of total nitrogen. Agricultural management, followed by dairy treat-ment fields (DTF), and then waste water treatment plants (WWTP) inflows are the largest contributors of nutrients into Waco Lake. Removing small flood control reser-voirs (U.S. Soil Conservation Service PL-566 design) resulted in an 82% increase in total phosphorus and a 92% increase in total nitrogen, while the removal of other anthropogenic features resulted in decreased nutrient loading. PL-566 reservoirs store nutrients in the watershed, and are probably useful in pollution mitigation.