THE CONNECTICUT WATERSHED MODEL – MODEL DEVELOPMENT, CALIBRATION, and VALIDATION

Abstract

Nutrient loadings from watersheds within the state of Connecticut have a large impact on the water quality and aquatic health of Long Island Sound (LIS). Over the past 15 years, state and federal efforts have focused on improving the water quality and natural resources of LIS, with a specific emphasis on addressing the issue of hypoxia. In this study, funded by EPA and the Connecticut Department of Environmental Protection (CTDEP), a statewide watershed model was developed using the U.S. EPA Hydrological Simulation Program - FORTRAN (HSPF) and the U.S. Geological Survey's graphical user interface GenScn to quantify all sources of key nutrients to LIS. The Connecticut Watershed Model (CTWM) was developed to evaluate nutrient sources and loadings within each of six nutrient management zones that lie primarily within the state of Connecticut, and assess their delivery efficiency to LIS. The CTWM evolved by first performing calibration and validation on three small test basins across the state (Norwalk, Quinnipiac, and Salmon) representing a range of land uses, including urban, forest, and agricultural. The model was then extended to three major river calibration basins (Farmington, Housatonic, and Quinebaug) and subsequently expanded to a statewide model by using the most spatially applicable set of calibrated watershed parameters in non-calibrated areas. The user-friendly interface and framework of the CTWM was specifically designed to promote continuing use by CT DEP staff to assess multiple BMPs, implementation levels, and relative impacts of point source controls for nutrient reductions to LIS