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Project Summary

Full Summary

NJDEP commissioned Najarian Associates to conduct a hydrologic and water quality modeling study of the Great Swamp Watershed, located at the headwaters of the Upper Passaic River, New Jersey.

County: Morris

Town: Long Hill

NJDEP commissioned Najarian Associates to conduct a hydrologic and water quality modeling study of the Great Swamp Watershed, located at the headwaters of the Upper Passaic River, New Jersey.

Great Swamp Study Goals

The primary goal of the study was to assess the hydrologic and nutrient loading regime of the Great Swamp Watershed. Additional goals were to focus on the fate of nutrients within the Swamp and assess the impact of wastewater discharges within the watershed.

This analysis provided technical input for the NJDEP’s Upper Passaic Environmental Impact Statement and Northeast Water Quality Management Plan.

Technical Services

To support the model study, Najarian analyzed streamflows and water quality data for one year at locations near the outlet of and within the Great Swamp Watershed. The firm then adapted the USEPA-HSPF model to the entire 55-square mile Watershed using a detailed schematization of its land use and soils characteristics. This year-long simulation of continuous, real-time streamflow data allowed Najarian to analyze the Watershed hydrology.

Great Swamp Study Results

Model results indicated that the Swamp acts as a nutrient sink for both nitrogen and phosphorus, but that its removal capabilities may be reduced by increased flows from future development.

Great Swamp Study Follow-Up – Phase 2

Phase 2 included a follow-up study, initiated to provide micro-scale information on pollutant loadings as a function of land use. The study was commissioned by Long Hill Township under a 319(h) grant, and was endorsed by the Ten Towns Committee.

For the study, Najarian monitored six representative outfalls (with watersheds ranging from 19 to 253 acres) during two storm events. Using data collected from the study, the firm adapted the SWMM-IV model to each of these sub-basins and then used the calibrated model and an institutional GIS database to develop a generalized model for the overall watershed.

From the model simulation result, Najarian developed annualized loading statistics as a simple function of impervious cover. Thus, the study provided a straightforward way for planning agencies to assess the first-order impact of regional stormwater planning alternatives on water quality.