The Use of HydroWAMIT and WASP for Modeling Large Scale Watersheds in New Jersey

Total maximum daily loads (TMDLs) can become complex studies depending on the issues that need to be addressed. Many waterbodies in New Jersey are listed as impaired for phosphorus and dissolved oxygen (DO), making them central issues of the TMDLs. In order to address the total phosphorus and DO criteria established by the New Jersey Department of Environmental Protection (NJDEP), refined water quality simulations are necessary. The criteria for establishing the TMDL required that effects of phosphorus on algal productivity and diurnal variation of DO be accurately represented. In order to provide cost-efficient water quality simulations that meet DEP's requirements, a water quality model that can represent a refined stream network and multiple point sources was combined with simplified hydrologic simulation techniques. This combination of models operating at distinct scales allows the simulation of large-scale contributing watersheds and refined stream processes. The Water Quality Analysis Program (WASP) and the Hydrologic Watershed Model Integration Tool (HydroWAMIT) were used for two major TMDLs in New Jersey. The issues regarding the application of a modeling framework containing WASP and HydroWAMIT, the combination of refined water quality modeling with coarser hydrological inputs, model calibration overview, and the reasons why WASP and HydroWAMIT were preferred to other popular hydrologic models used for TMDLs are discussed in this paper.