Environmental Engineering Reference
In-Depth Information
Figure 9.6
Physical setting
and conceptual model of
recharge processes for a valley-
fill aquifer, northeastern United
States (after Kontis
et al
.,
2004
).
Recharge processes include: (1)
Recharge from unchanneled
runoff of adjacent upland areas;
(2) Recharge from seepage from
tributary streams draining the
uplands; (3) Recharge directly
from precipitation;
(4) Subsurface interaquifer flow
to the aquifer from bedrock;
and (5) Perennial streams can
be sources of recharge under
pumping conditions when
groundwater levels fall below
the stream.
1
2
3
4
5
Lithology
Hydraulic conductivity
Very fine sand, silt, clay
Sand
Low
Medium
Gravel and sand
Medium to high
Till
Bedrock
Low
Very low
model (
Section 3.5
) to estimate recharge in the
Mirror Lake watershed in the range of 260 to
280 mm/yr.
on the basis of data collected at 55 streamflow
gauging sites on unregulated streams in New
Hampshire. Average annual recharge was esti-
mated at 530 mm; about 43% of that recharge
occurred in spring, with the remainder occur-
ring somewhat uniformly throughout the other
seasons. Kontis
et al
. (
2004
) linked a ground-
water-flow model of the drift aquifer system
in Dover, New Jersey, with a water-budget
analysis of adjacent uplands and found that
approximately 32% of recharge to the aquifer
came from upland sources. Knott and Olimpio
(
1986
) applied the tritium-profile method, using
tritium concentrations in groundwater, and
estimated a recharge rate of 680 mm/yr (68%
of precipitation) for a sand and gravel aquifer
on Nantucket Island, Massachusetts. Mau and
Winter (
1997
) compared results obtained from
multiple streamflow hydrograph-analysis meth-
ods with data from the Mirror Lake watershed
in New Hampshire. Tiedeman
et al
. (
1997
) used
inverse modeling with a groundwater-flow
9.4.10 Atlantic and Gulf Coastal Plain
The Atlantic and Gulf Coastal Plain covers an
area in excess of 1 000 000 km
2
that stretches
from the southern tip of New York to the south-
ern tip of Texas. The area is relatively flat,
reaching elevations of only 100 to 250 m above
sea level along its inner margin. Groundwater
occurs in unconsolidated sediments (sand,
silt, and clay) that were originally transported
by streams from adjacent uplands. The sedi-
ments can obtain substantial thickness along
the seaward edge of the region and along the
axis of the Mississippi embayment. In south-
ern Louisiana, the sediments exceed 12 000 m
in thickness (Heath,
1984
). The geologic for-
mations dip toward the sea or the axis of the
Mississippi embayment. The climate is humid
except for the southern tip of Texas, where it
