Ground-water development in East St. Louis area, Illinois. Urbana, IL ...

Generally ground-water recharge in the East St.
Louis area is greatest in spring and early summer
months of heavy rainfall and least in the late summer,
fall, and winter months. Most recharge occurs during
spring months when evapotranspiration is small and
soil moisture is maintained at or above field capacity by
frequent rains. During summer and fall months evapotranspiration
and soil moisture requirements have first
priority on precipitation and are so great that little precipitation
percolates to the water table except during
periods of excessive rainfall.
Recharge directly from precipitation was estimated
by flow-net analyses of the piezometric surface in the
vicinity of the Wood River, Granite City, National City,
and Monsanto area pumping centers. The quantity of
water percolating through a given cross section of an
aquifer is proportional to the hydraulic gradient (slope
of the piezometric surface) and the coefficient of transmissibility,
and it can be computed by using the following
modified form of the Darcy equation (see Ferris,
1959).
where:
Q = TIL (10)
Q = discharge through flow cross section, in gpd
T = coefficient of transmissibility, in gpd/ft
I = hydraulic gradient, in ft/mi
L = width of flow cross section, in mi
The rate of recharge directly from precipitation can be
estimated on the basis of the difference in discharge of
water through successive flow cross sections with the
following equation (Walton, 1962):
where:
(11)
The + sign is used when there is a water-level rise and
the — sign is used when there is a water-level decline.
Flow lines were drawn at right angles to the estimated
piezometric surface contours for December 1956,
June 1961, and June 1962 toward cones of depression
in the Wood River, Granite City, National City, and
Monsanto areas to delimit the flow channels in figures
52 through 54. The locations of flow channels were so
chosen that recharge rates under all types of geologic,
hydrologic, and land use conditions could be studied.
The discharges through cross sections A—A', B—B',
C—C', D—D', E—E', F—F', G—G', and H—H' were
computed using equation 10 and figures 25 and 52
through 54. Differences in discharge of water through
successive flow cross sections were determined. Average
rates of water-level declines or rises within flow channel
areas were estimated from hydrographs of observation
wells. Surface areas of flow channels were obtained
from figures 52 through 54. The average coefficient of
storage of the coarser deposits was estimated to be 0.20
on the basis of aquifer-test data, and the average coefficient
of storage of the finer grained alluvium was estimated
to be 0.10 on the basis of studies by Schicht and
Walton (1961). The data mentioned above were substituted
in equation 11, and recharge rates for each flow
channel area were computed.
Recharge rates vary from 299,000 gpd/sq mi in the
National City area to 475,000 gpd/sq mi in the Wood
River area. The average rate of recharge in the East St.
Louis area is 371,000 gpd/sq mi. The East St. Louis area
covers about 175 square miles. It is estimated that total
recharge directly from precipitation to the East St.
Louis area averages about 65 mgd.
The subsurface flow of water from the bluff was
estimated by studying the movement of water through
flow channels near the foot of the bluff. Flow lines were
drawn at right angles to the bluff and the estimated
piezometric surface contours for June 1961 and June
1962 to delimit the flow channels shown in figures 53 and
54. The discharge through cross sections I—I', J—J',
and K—K' were computed using equation 10 and figures
25, 53, and 54. Average rates of water-level declines or
rises within flow channel areas were estimated from
hydrographs of observation wells. The average rates of
changes in storage within flow channel areas were computed
as the products of water-level changes, storage coefficients,
and flow channel areas. Recharge directly from
precipitation within flow channel areas was estimated as
the products of the average recharge rate (371,000
gpd/sq mi) and flow channel areas. Recharge and
changes in storage within flow channel areas were subtracted
from the discharges through cross sections I—I',
J—J', and K—K' to compute rates of subsurface flow of
water from the bluff. The average rate of subsurface flow
of water from the bluff is 329,000 gpd/mi. The length of
the bluff forming the eastern boundary of the East St.
Louis area is 39 miles. Thus, the total rate of subsurface
flow of water from the bluffs is about 12.8 mgd.
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