Section 1. The Watershed Today
SURFACE AND
GROUNDWATER WITHDRAWALS
The Schuylkill River and its tributaries are an essential source of water
supply for people living and working in the watershed. Power-generating plants
are the largest water consumers, accounting for about 44 percent of the total
withdrawals. Additional power plants are under consideration. Public water
suppliers, providing water to residential and non-residential customers, are
the second principal water users in the watershed. Over 85 percent of the
public water supplies serve the needs of nearly 1.5 million people in the
Philadelphia metropolitan region.
In 1995, surface water accounted for 83 percent of the water withdrawals in the watershed, with the remaining 17 percent coming from groundwater. Between 1985-95, surface water withdrawals increased by 6 percent, whereas groundwater withdrawals increased by 31 percent. Increasing reliance on groundwater is occurring at the same time that development trends are creating more impervious cover that interferes with the natural recharge of groundwater from precipitation. In turn, reduced recharge will lower the groundwater table and thereby reduce “base flow” of water flowing in streams between periods of precipitation.
Typically, water consumption peaks in the summer months, just as low flows occur in the river. These seasonal imbalances are particularly evident in the Philadelphia area, as shown by the accompanying chart of water treatment plant withdrawals and river flow conditions. Unless we manage the Schuylkill’s surface and groundwaters as one integrated system, we are likely to see a simultaneous increase in groundwater demand with a corresponding decrease in groundwater supply.
Figure
10.
Seasonal Relationships
Between Water Withdrawals
and River Flow
Source: Philadelphia Water Department
Seasonal Imbalances in Water Withdrawals and River Flow. 1998-2000 average monthly pumping rates (mgd) from the Philadelphia Water Department’s Belmont and Queen Lane treatment plants compared with long-term normal Schuylkill River flow rates (cfs) at Fairmount Dam. Source: Philadelphia Water Department.
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