Flow and Water Quality Modeling of Passaic River Watershed

A Progress Report (August 2001)

Qizhong Guo and Chenchen Li

Summary

As the first step, the New Jersey version of BASINS (NJWS or BASINS-NJ) was applied to model water flow and fecal coliform count in the Whippany River watershed upstream of Morristown. In the modeling, the watershed was delineated into five subwatersheds based on HUC-14 hydrologic boundaries (Figure 1), and the stream network was divided into five reaches accordingly (Figure 2). Through adjustments of model hydrologic parameters, daily flow rate was modeled reasonably well in comparison to measured data from years 1992 to 1997 (Figure 3). Through adjustments of fecal coliform loading rates from failing septic tank and wastewater treatment plant effluent, fecal coliform count during low flow (when people would have actually been swimming and fishing) was modeled reasonably well in comparison to measured data (Figure 4). Through adjustments of fecal coliform loading rates from stormwater runoff,  fecal coliform count during high flow was also modeled reasonably well in comparison to a limited number of measured data points (Figure 4).

The BASINS tool is expected to be applicable to the Passaic River watershed upstream of Paterson for the initial assessment and modeling purposes. The calibrated hydrologic and water quality coefficients for the Whippany River watershed are also expected to be applicable, after minor adjustments, to the Passaic River watershed upstream of Paterson. The degrees to which flow and water quality might have been affected by wetlands and water withdrawal in the Passaic River upstream of Paterson could also be initially assessed using the BASINS tool. For example, BASINS could be used as a tool for analysis of mass balance (or unbalance) under various monitored and modeled flow conditions. With these expectations in mind, modeling of the Passaic River upstream of Paterson has been initiated. The automatic delineation function in BASINS 3.0 (beta version) has been used to delineated the Passaic River watershed upstream of Paterson from digital elevation model grid files. WinHSPF model in BASINS 3.0 has been used to simulate surface water withdrawal (such as drinking water treatment plant intake withdrawal) by modification of the user input file. Field data on flow, fecal coliform, and total organic carbon (TOC) in Passaic River at Little Falls (location of the existing long-term USGS flow and water quality station closest to Paterson) have also been analyzed from the modeling perspectives (Figures 5 and 6). Figure 5 indicates: (1) The fecal coliform standard was violated during both low and high flows, and (2) Measured data are available during both low and high flows for the model calibration purposes. Figure 6 indicates: (1) The assumed TOC standard (4 mg/L) was violated during both low and high flows, and (2) The measured data are available during both low and high flows for the model calibration purposes. TOC is a precursor to formation of disinfection byproducts through drinking water treatment plant and distribution system.

Due to the natural and planning complexities of the Passaic River watershed, modeling modules more advanced than those currently included in BASINS 3.0 are expected to be needed in the future, at least for some segments and/or characteristics of the watershed. With these expectations in mind, assessment of the more advanced modeling modules such as those included in EFDC, MIKE, and WARMF has also been initiated.  

Figure 1. Delineation of Whippany Watershed Upstream of Morristown
into Five Modeling Subwatersheds

 Figure 2. Segmentation of Whippany River Network into Five Modeling Reaches

Figure 3. Comparison of Modeled and Measured Daily Flow Rates
in Whippany River at Morristown from years 1992 to 1997

Figure 4. Comparison of Modeled and Measured Daily Fecal Coliform Counts
in Whippany River at Morristown from years 1992 to 1997

Figure 5

Figure 6