A combined watershed–water quality modeling analysis of the Lake Waco reservoir: I. Calibration and confirmation of predicted water quality

A coupled watershed–reservoir modeling system was applied to the Lake Waco reservoir and watershed to test possible sources of seasonal excess nutrient concentrations in Lake Waco. The Soil Water Assessment Tool (SWAT) was used for modeling watershed production of water and nutrients. This model included small lakes and dairies in the watershed, located spatially using geographic data. For the reservoir, the 2-dimensional, hydrodynamic model CE-Qual-W2 was used with inputs derived from the SWAT simulations. Calibration of the models was based on observed hydrographic information and stream and reservoir nutrient data. The relationship between predicted and observed stream flow values for the North Bosque River, the major tributary to the reservoir, were highly correlated (r 2= 0.86) for the calibration period 1997–1998. Predicted daily nutrient values near the inflow of the North Bosque into Lake Waco reservoir were variable but similar to previously estimated annual loading values. Comparison of predicte...