The Northease AVGWLF: A Watershed Scale Model to Predict Sediment and Nutrient Transport

The New England Interstate Water Pollution Control Commission (NEIWPCC) is collaborating with Pennsylvania State University (Penn State) to develop the Generalized Watershed Loading Function with an ArcView (AV) geographic information systems (GIS) interface (AVGWLF) for the New England states and New York State. The Northeast AVGWLF is a calibrated, watershed-scale model that uses hydrology, land cover, soils, topography, weather, pollutant discharges, and other critical watershed-related characteristics to model sediment and nutrient transport within a watershed. AVGWLF is a powerful tool that will provide its user with a means for quantifying pollutant loads within a watershed and to evaluate various strategies to mitigate water quality impacts.

NEIWPCC selected 27 watersheds in the region for the purpose of calibrating and validating the model. The 27 watersheds were selected to represent the assortment of landscape characteristics that exist in the region; each watershed also had to meet a minimum threshold for available historic water quality and flow data. Approximately half of these watersheds will be used to calibrate the model, the remaining watersheds will be used to validate the model.

The 2004 Nonpoint Source, Section 319 Guidelines reiterate the U.S. Environmental Protection Agency’s (USEPA) assertion that, the most effective way to achieve enhanced water quality is by developing management approaches at the watershed scale, rather than site by site. The Section 319 Guidelines recommend the development of watershed-based plans that address nine components, including an estimate of pollutant load reductions expected from the implementation of specific management measures. Quantifying pollutant load reductions is essential for assessing and measuring the effectiveness of best management practices (BMPs) and permits. The states and USEPA also use these quantified estimates for tracking the success of 319 projects and for Total Maximum Daily Load (TMDL) implementation.

The states often rely on models to assist in the accurate quantification of pollutant load reduction estimates. The goal of this project is to provide NEIWPCC’s member states (Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island, and Vermont) with a common management tool for developing nonpoint source pollutant load reduction estimates and TMDLs for nutrients and sediments at the watershed and regional scales.

The AVGWLF model will provide the states with a cost effective means of developing pollutant load reduction estimates for accurate 319 reporting. Further, the model will enhance the states ability to develop TMDLs for waters impaired primarily by nonpoint sources. The AVGWLF modeling approach was successfully used to quantify nutrient and sediment loads and develop TMDLs for approximately 66 nonpoint source impaired segments in the Neshaminy Creek Watershed, which is located north of Philadelphia, Pennsylvania. NEIWPCC’s member states will be able to use the Northeast AVGWLF for bundling TMDLs, which is essential given the region’s limited resources for TMDL development.

The Northeast AVGWLF will provide the states and their partners with an enhanced technical “tool kit” for use in the modeling of nonpoint source pollutant load reduction scenarios and for the development of Total Maximum Daily Loads (TMDLs). The goal of the development of the Northeast AVGWLF is to assist the New England states and New York State to more effectively implement their water quality programs, while encouraging the implementation of these programs on a watershed, interstate, and regional scale. The Northeast AVGWLF will not only provide this region with a common tool to develop pollutant load reduction estimates and TMDLs, it will also provide regional users with a common database, ultimately enhancing and promoting interstate collaboration on the management and improvement of water quality throughout New England and New York State.

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