Delaware & Raritan Canal Tributary Assessment and Nonpoint Source Management Study

The Delaware & Raritan Canal was constructed in 1834 and operated as a barge canal until 1932.  The present Canal Water Supply Transmission Facility is 60 miles long with its Delaware River intake at Bulls Island in Hunterdon County (north of Stockton Borough) and its outlet at the Raritan River in the City of New Brunswick. Flow between the Canal and the rivers is regulated by control gates installed in the original lock structures.  In addition, several streams and stormwater systems are tributary to the Canal and contribute water. 

D & R Canal at 10-Mile Lock

The Canal was designated as a State Park in 1974, and is also listed on the State and Federal Registry of Historic Sites.  The entire length of the Canal is classified as FW2-NT by the New Jersey Department of Environmental Protection (NJDEP).   In 1981 the operation of the Canal as a water supply was transferred to the New Jersey Water Supply Authority (NJWSA).  Today, the Canal transfers water from the Delaware River Basin to the Raritan River Basin, where the raw water is treated to become drinking water for approximately 600,000 people living in Central New Jersey, including customers of New Jersey American Water Company (formerly  Elizabethtown Water Company), Middlesex Water Company, the Township of North Brunswick and the City of New Brunswick.

Since 1997, several of the Canal’s water purveyors reported increased concentrations of total suspended solids in the raw water during and immediately after precipitation events, requiring increased chemical use for treatment and increasing residual sludge generation.  A 1999 study by the United States Geological Survey (USGS) reported that the turbidity does not decrease in the Canal reach between Ten Mile Lock (near Exit 12 of Route 287) and the Route 18 spillway (border of New Brunswick) as would be expected due to low water velocities in this reach, indicating that settling solids are replaced by particulates from influent streams and stormwater discharges to the Canal.  Field observations downstream of the Canal’s confluence with Cedar Grove Brook confirm this, noting the formation of a sand bar indicating that Cedar Grove Brook contributes sediment-laden stormwater to the Canal. 

The USGS study found twelve “infalls” to the Canal, none of which were known point sources of treated or untreated effluent to the Canal – the problem apparently is caused entirely by nonpoint source pollution. The water supply intakes for New Brunswick and Middlesex Water Company are near the end of the Canal, and are directly affected by pollutant loads to the section of the Canal that was the subject of this study.

In 2001, the New Jersey Water Supply Authority (NJWSA) received funding from the NJDEP under the Section 319(h) Nonpoint Source Pollution Grant Program for the “Delaware & Raritan Canal Tributary Assessment and Nonpoint Source Management Study."  The project identified a number of priority issues:

Protection of the Canal for drinking water supply and recreational uses.

Identification and assessment of influent flows to the Canal and their impact on Canal aesthetics, water quality, and drinking water treatment.

Development of a nonpoint source pollution management plan for each tributary area with significant pollutant loads, which will include conceptual designs of BMPs and other controls to reduce total suspended solids and associated pollutant loadings to the Canal.

The project area includes the final eleven miles of the Delaware and Raritan Canal between Amwell Road in Franklin Township and Landing Lane in the city of New Brunswick.  The combined drainage areas of the infalls to the Canal in this reach is approximately 1,500 acres in Franklin Township and South Bound Brook Borough, Somerset County.  The project area ends just upstream of the drinking water intakes for Middlesex Water Company and the City of New Brunswick.  New Jersey American Water Company also has the ability to take water from the Canal near 10-Mile Lock. 

The project tasks included:

Public Outreach:  A project committee was formed that included representatives from NJWSA, NJDEP-DWM, South Bound Brook Borough and Franklin Township.  The committee met several times to provide updates on project progress and for NJWSA to receive input on project results and next steps.

Baseline Water Quality Assessment:  The Canal is a unique waterbody in New Jersey.  It provides potable water to approximately 600,000 residents of Central New Jersey, making it a critical water supply. However, there are no NJDEP AMNET or NJDEP/USGS Cooperative Water Quality Monitoring Program stations on the Canal.  Some parts of the Canal are monitored by public community water supply systems, Middlesex Water Company in particular.  NJWSA obtained available water quality data from New Jersey American Water Company, Middlesex Water Company and the USGS to prepare a baseline assessment for comparison with post-BMP installation monitoring data.

Compilation of Existing Land Use/Land Cover Data:  NJWSA utilized the 2002 aerial photography available from NJDEP and Franklin Township for this project.  Based on the aerial photography, field observations and information from the municipalities, the existing land use data were updated to a limited extent to more accurately reflect existing conditions.

Field Reconnaissance to Identify Infalls:  NJWSA’s project began with field reconnaissance to identify all infalls to the Canal within the study area. The 1999 USGS study identified twelve infalls to the Canal in the project study area.   A total of 69 infalls were identified during the field reconnaissance. Each infall was photographed and located with GPS.  Infall identification was complicated by the lack of a comprehensive stormwater system map and the fact that portions of the stormwater system are channeled underneath the Canal for discharge into the Millstone or Raritan Rivers.  

Delineation of Drainage Areas for Infalls:  NJWSA delineated the drainage area for each infall using Watershed Delineator, an ArcView GIS extension.  The drainage area for each infall was field verified by NJWSA personnel.

Modeling of Flows and Loads for Infalls:  NJWSA and Princeton Hydro/SWM used  WinSLAMM (Source Loading and Management Model for Windows) to estimate the runoff, sediment and phosphorus loads from each drainage area.  WinSLAMM allows the user to divide each land use (residential, commercial, industrial, open space, institutional and freeway) in the drainage area into runoff and pollutant source areas (parking areas, roof, landscaped areas, driveways, undeveloped, etc.).  The model then calculates total runoff volume and pollutant load for the entire drainage area, as well as how much of each originates from each land use and from each source area within the drainage area. 

Recommendations of Best Management Practices for High Priority Infalls:  Based on the results of the WinSLAMM modeling, Princeton Hydro/SWM and NJWSA prioritized the infalls, and then analyzed a series of alternative stormwater BMPs using WinSLAMM for the top 15 infalls.  These BMPs, which included both structural and nonstructural measures, were chosen to reduce the runoff-borne particulate pollutant load to the Canal. The BMPs analyzed included four street-sweeping scenarios, impervious area disconnection within different types of land uses, and the use of manufactured treatment devices throughout each drainage area as well as wet ponds, constructed wetlands and sand filters at the downstream end of each drainage area at the Canal infall.  Based on the results of these analyses, a set of recommendations for reducing particulate loads to the Canal were developed for the top 15 infalls.

The watershed protection and restoration plan that was developed as part of this project is currently under review by NJDEP.  NJWSA will be working with Franklin Township, South Bound Brook Borough, Somerset County and other groups within the project area to secure funding and begin implementation of the recommended projects.

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