Hydrological and Water Quality Assessment in a Suburban Watershed with Mixed Land Uses Using the SWAT Model

This study applied the Soil and Water Assessment Tool (SWAT) to the Neshanic River watershed, a suburban watershed with mixed land uses in Central New Jersey, United States. The urban lands were prominently in low-density residential development. The simulated streamflow and water quality parameters including total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) were compared to those of the measured values in the watershed. The Nash-Suttcliffe efficiency was 0.60 for daily streamflow and 0.68 for monthly streamflow during the calibration period 1997–2002, and 0.37 and 0.69 during the validation period 2003–2008, respectively. The model satisfactorily simulated the streamflow, but underestimated the streamflow variability (i.e., the flashiness of this suburban watershed). The measured water quality data at seven locations in the watershed were in general agreement with their corresponding simulated values, but the agreement varied by pollutant. The observed and simulated values show the most consistent agreement in TN, followed by TP and TSS. With the embedded algorithms and parameters used to simulate the hydrological and water quality responses in urban lands, the SWAT model reasonably simulated the hydrological and water-quality conditions in this suburban watershed. The modeling results confirmed that both TSS and TP were water-quality concerns under the current land-use and management conditions in the watershed. Management measures should be implemented to achieve 9% load reduction for TSS and 49% load reduction for TP to meet the required water-quality standards in the watershed.