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Raritan Basin Reservoir Levels & Drought Conditions

Spruce Run and Round Valley Reservoirs


The Spruce Run and Round Valley Reservoirs(click for map) are part of the New Jersey Water Supply Authority’s Raritan Basin Water Supply System(click for map) which serves 1.5 million residents of central New Jersey. Both reservoirs are located in western Hunterdon County within Clinton Township and Union Township. The reservoirs are connected to natural river systems, which enable water to be stored and moved around within this service area. Balancing the needs of everyone that relies on this water is a critical part of the Authority’s work.

About the Raritan Basin Reservoirs

Both reservoirs were constructed by the State of New Jersey in the 1960s following a historic drought. The Authority was created in 1981 to operate the reservoirs and associated infrastructure as sources of raw drinking water. The Authority also operates the Delaware & Raritan(D&R) Canal and the Manasquan Reservoir. The Authority is a State Government Authority that is “in but not of” the New Jersey Department of Environmental Protection (NJDEP). The NJDEP Commissioner is the Chair of the Authority’s Board.

The Spruce Run Reservoir is an “on-stream” reservoir that holds up to 11 billion gallons of water. It is fed entirely by rain flowing through several streams including the Spruce Run and the Mulhockaway Creek. The watershed drainage area of the Spruce Run Reservoir is 41 square miles and encompasses parts of five municipalities. Water is released daily from the reservoir back into the Spruce Run, which enters the South Branch of the Raritan River in the Town of Clinton. The South Branch and the North Branch of the Raritan River converge in Branchburg Township (Somerset County), forming the Raritan River. Water purveyors withdraw and treat water from the Raritan River after its confluence with the Millstone River to provide to the public as drinking water.

The Round Valley Reservoir is an “off-stream pump storage” reservoir that holds up to 55 billion gallons of water. Because there are no streams feeding this reservoir it has a small natural drainage area of about five square miles and is fed almost entirely by manual transfer of water from the South Branch of the Raritan River. The Authority operates a pumping station in the Hamden section of Clinton Township to move water from the river into the reservoir via a large underground pipeline. The pumping station contains ten large pumps. How much water is pumped and when it is pumped is dependent on a number of factors, the most critical of which is the presence of sufficient flow in the South Branch of the Raritan River. Water is typically released from Round Valley by an underground pipeline that empties into the South Branch of the Rockaway Creek. The Rockaway Creek eventually empties into the North Branch of the Raritan River, which joins the South Branch to form the Raritan River in Branchburg Township (Somerset County). Water purveyors withdraw and treat water from the Raritan River after its confluence with the Millstone River to provide to the public as drinking water. 

Both Spruce Run Reservoir and Round Valley Reservoir are designed for water supply purposes, but are also managed for recreational activities such as fishing, boating, hiking, and camping. The NJDEP Division of Fish and Wildlife manages the fishery at Round Valley Reservoir and the NJDEP State Park Service manages the other recreational aspects of both reservoirs.

About Reservoir Releases

The Authority is required to release enough water daily to maintain “minimum passing flow rates” in downstream areas of the Raritan Basin System. These minimum passing flows are required to be maintained while anticipating the volume of water that will be used by the downstream purveyors because minimum passing flows are measured at points upstream and downstream of the water treatment plant intakes. The minimum passing flow rates are set by the NJDEP and are designed to protect the availability and quality of water and the ecology of streams. Stream flow gauges, operated by the United States Geological Survey, are located throughout the downstream areas. A map of stream and rainfall gauges and the associated data can be accessed at http://www.raritanbasin.org/USGSGauges.html.

The Authority maintains daily records of reservoir levels and releases, and that information can be accessed at http://www.njwsa.org/Data.htm. It is always the Authority’s goal to release as little as possible. 

About the Drought

April 13, 2017

The NJDEP lifted a “Drought Warning” yesterday for 12 of 14 counties in the northern, central and northern coastal regions of New Jersey and removed a drought watch for four counties in the southwestern part of the state.

Round Valley and Spruce Run reservoirs both remain below normal capacity. Round Valley is at about 72 percent capacity and Spruce Run is at about 69 capacity, due in large part to less precipitation in this area over the winter. As a result, Hunterdon County and Somerset County, which are primarily served by these reservoirs, remain under a drought warning. This allows for continued reduced passing flows downstream, which are designed to conserve storage in the reservoirs.

November 17, 2016

The NJDEP declared a “Drought Warning” for much of New Jersey on October 21, 2016. The Authority’s Raritan System is responsible for supplying raw water to the majority of the “Central” region of the State.   The Drought Warning designation enables the NJDEP to more closely manage reservoir systems by directing water transfers among systems, controlling releases from reservoirs, and modifying the minimum passing flows in streams and rivers in order to balance ecological protection and needs of water suppliers. The goal of the drought warning is to preserve and balance available water supplies in an effort to avert more serious water shortages in the future. 

As an on-stream reservoir that is entirely dependent on rainfall, Spruce Run is extremely susceptible to seasonal fluctuation in water level based on weather patterns. Over extended periods of time, higher rainfall amounts result in a fuller reservoir, and lower rainfall amounts result in a less full reservoir. Round Valley is also very dependent on rainfall in that the ability to fill it is based on adequate stream flow in the South Branch of the Raritan River. Stream flow is directly related to rainfall. Mandatory releases from both reservoirs are regulated by the NJDEP and are necessary to ensure that downstream areas have adequate water supply and water quality.

The significant rainfall deficiencies in New Jersey have required the Authority to release more water than usual from Round Valley and Spruce Run Reservoirs to maintain the necessary flows in downstream rivers. As of mid-November 2016, the Authority is still releasing water from the reservoirs, although the releases are now less than levels required in the heat of the summer since water use is down in the cooler weather.  Further, as a result of the drought warning issued by the NJDEP, the minimum flow requirements in the rivers have been reduced, allowing the Authority to conserve some water. 

 Upcoming Project at Round Valley

The Authority is planning a major project at Round Valley that will possibly require the reservoir to be lowered during construction, but all water releases in 2015 and 2016 from Round Valley have been for drinking water use and to meet passing flow requirements. 

All additional information about the upcoming project at Round Valley can be found at the project website at:  http://www.njwsa.org/html/rv_project.html.

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