Public water supply in the Rockaway River valley depends almost entirely on ground water from wells in the valley-fill deposits. Ground-water withdrawals from these deposits in 1986 were about 9.1 million gallons per day. A steady-state ground-water flow model was developed to quantify the effects of ground-water withdrawals on water levels in the valley-fill aquifers and on ground-water discharge to the Rockaway River. The ground-water-flow model, which represents an aquifer system consisting of an unconfined and a confined aquifer separated by a discontinuous confining unit, was implemented to examine aquifer resonse to current and predicted ground-water withdrawals in areas of proposed well sites and the effect of increased ground-water withdrawals on ground-water discharge to the river. Ground-water flow to wells in the valley-fill aquifers is sustained by increased vertical flow between the two aquifers, the diversion of ground water that had discharged to the Rockaway River, and induced seepage resulting from pumping near the Rickaway River. If the rate of ground-water recharge decreases or if the rate of ground-water withdrawals from the valley-fill aquifers increases, ground-water discharge to the Rockaway River above the Boonton Reservoir will decrease by an equivalent amount. The average annual base flow of the Rockaway River above the Boonton Reservoir will meet the minimum passing flow requirement of 7 million gallons per day under conditions of average annual ground-water recharge, and increased ground-water withdrawals anticipated by the years 2000 and 2040. For anticipated increases in withdrawals to 11.5 million gallons per day by the the year 2000, and 14.6 million gallons per day by the year 2040, base flow to the Rockaway River above the Boonton Reservoir may not be sufficient to meet the minimum required reservoir outflow during extended periods of decreased recharge, such as drought, as much as 5 and 11 percent of the time, respectively.