USING THE WATER EROSION PREDICTION PROJECT (WEPP) MODEL TO ASSESS EROSION POTENTIAL AND SEDIMENT LOADING OF THE GRASSE RIVER, ST. LAWRENCE COUNTY, NEW YORK

The Water Erosion Prediction Project (WEPP) Model is a web-based soil erosion simulation model built on the fundamentals of hydrology, plant science, hydraulics, and erosion mechanics. It requires five data inputs: USGS 30m DEM, climate, soil, land use, and land management. The model simulates sediment transport and deposition in a channel. Outputs include soil loss from hillslopes, sediment yield at the base of hillslopes, precipitation volume, runoff volume, and watershed area for the delineated channel networks. The Grasse River (St. Lawrence Watershed, New York) is being evaluated for soil erosion potential, sediment loading, and nutrient loading to assess stream health. This project is related in part to the US Army Corps of Engineer’s (USACE) Great Lakes Tributary Modeling (GLLTM) 516e Program. The WEPP model selects assessment locations, generates modeling output data, and helps assess field data. The WEPP evaluated a tributary that runs into the Grasse River near the SUNY Canton campus. It determined that this watershed has an area of 549.1 ha, discharge of 9.92x10⁵m³/yr, precipitation of 874 mm/yr, 9 channels, and 23 hillslopes. Primary soil types include fine sandy loam, silty clay loam, and silty clay. Land use consists of 79% pasture/hay, 18.1% cultivated crop, and 1.9% deciduous forest with good grass, corn-soybean-fall mulch till, mature forest, poor grass, and shrubs as groundcover. Sediment yield ranges from 2364 tonne/yr - 3706 tonne/yr and soil loss ranges from 0-176.4 tonne/yr. Water quality testing shows the impact that erosion is having on the watershed with average values as follows: 574.75 mg/L TDS, 7.84 mg/L TSS, 812 μS conductivity, 39.55 NTU turbidity, and 6.97 mg/L DO. Nutrient analysis for nitrate, nitrite, total phosphate, orthophosphate, and sulfate, which ranged from 0.53 mg/L to 230 mg/L. This data supplements the WEPP model outputs and indicates that sediment and nutrient loading is present. One-way ANOVA tests for variance indicate that tributary water quality data is significantly different than Grasse River water quality (p-values < 0.05, a = 0.05) with greater concentrations of sediment, nutrient parameters and lower DO levels. The watershed could be contributing to sediment and nutrient loading in the Grasse River. Additional watersheds are being evaluated with the WEPP model.