The water supply for the city of Madison, Wisconsin, and for surrounding municipalities is obtained from the ground-water reservoir that underlies the area. This ground-water reservoir is composed of an upper aquifer and an underlying sandstone aquifer. High-capacity water-supply wells pump from the sandstone aquifer.
Pumping from the sandstone aquifer has resulted in hydrologic changes. The water level has dropped in both the upper aquifer and underlying sandstone aquifer, and the flow of water in streams has been reduced.
The effects of anticipated pumping were examined with the use of a digital model. The maximum water-level decline from the beginning of pumping in 1882 until 1975 was about 75 feet in the sandstone aquifer and 10 to 20 feet in the upper aquifer. Additional declines between 1975 and 2000 were computed to be 10 to 30 feet in the sandstone aquifer and 5 to 10 feet in the upper aquifer. The average annual streamflow of the Yahara River at the McFarland gaging station was reduced 32 percent from the beginning of pumping to 1975. An additional 7 percent reduction in streamflow was computed for the period 1975 to 2000.
