Science Center Objects

Hydrogeology of, and Simulated Groundwater Flow, in the Valley-Fill Aquifers of the Upper Rockaway River Basin, Morris, New Jersey

By Alison Gordon

 

MODEL VERSION/TYPE: MODFLOW-96, transient

AREA STUDIED: Rockaway Township, Morris County

AQUIFERS SIMULATED: Glacial aquifer

MOST RECENT WITHDRAWALS SIMULATED: 1986 (original), 1998 (updated)

MODEL SIZE: 2 layers, 85 rows, 96 columns

MINIMUM GRID SPACING:500 feet x 500 feet

MODEL ARCHIVE is available by email request at gs-nj-model-request@usgs.gov

 

Public water supply in the upper Rockaway River valley in Morris County, New Jersey, is obtained largely from groundwater withdrawals from the valley-fill aquifers. These withdrawals have increased from about 3 million gallons per day in 1950 to more than 9 million gallons per day in 1986. Groundwater is withdrawn from valley-fill sands and gravels, which comprise an upper and a lower aquifer. These aquifers are separated by a discontinuous confining unit that consists mostly of silt and clay. Increases in groundwater withdrawals can induce movement of water from streams to wells, increase flow from the upper aquifer to the lower aquifer, and reduce streamflow downstream from the Boonton Reservoir.

A groundwater-flow model was used to simulate and quantify the effects of current and predicted withdrawals on the groundwater flow system under steady-state conditions. Under current (1986) conditions, an average of 9.1 million gallons per day is withdrawn from the valley-fill aquifer system. Average groundwater discharge to the Rockaway River upstream from the Boonton Reservoir of about 37.2 million gallons per day is sufficient to maintain the court-ordered passing flow requirement of 7 million gallons per day that is mandated to dilute effluent discharge downstream from the reservoir. Some reaches of the Rockaway River and its tributaries lose water to the upper aquifer at the pumping centers of the Town of Dover, Boonton Township, and Wharton and Rockaway Boroughs. Vertical flow from the upper aquifer to the lower aquifer has increased near areas of groundwater withdrawals.

Results of simulations show that the average groundwater discharge above the Boonton Reservoir will sustain the mandated minimum flow rate downstream from the reservoir if groundwater withdrawals from the valley-fill deposits increase to 11.5 million gallons per day, as anticipated by the year 2000, and also if groundwater withdrawals increase to 14.6 million gallons per day, as anticipated by 2040. Under pumping conditions modeled for 1986-2040, streamflow depletion will continue near the well fields in the Town of Dover, Boonton Township, and Wharton Borough. Relocation of the Rockaway Township well field to the north of its current site probably will cause a loss in streamflow in the Beaver Brook tributary in Rockaway Township. Total streamflow loss from river reaches between the Town of Dover, Rockaway and Denville Townships, and Rockaway Borough pumping centers will increase by about 1 million gallons per day from 1986 to 2000, and about 2.4 million gallons per day from 1986 to 2040 as a result of pumping at the Town of Dover, Rockaway and Denville Townships, and Rockaway Borough pumping centers.