Environmental Engineering Reference
In-Depth Information
1200
Figure 3.15
PRMS simulated
and daily mean measured
streamflow at Sagehen Creek for
water years 1982 through 1988
(Markstrom
et al
.,
2008
).
Daily mean
Simulated
800
400
0
1982
1983
1984
1985
1986
1987
1988
Water year
400
400
Figure 3.16
GSFLOW simulated
fluxes of gravity drainage through
soil-zone base and groundwater
discharge into the soil zone for water
years 1981 through 1989 (Markstrom
et al
.,
2008
).
Gravity drainage through soil-zone base
Groundwater discharge to soil zone
300
300
200
200
100
100
0
0
Water year
resulting in more than 6000 time steps for the
simulated period of record. The calibration pro-
cess was fully described by Markstrom
et al
.
(
2008
). Simulated streamflow was generally in
good agreement with measured streamflow
(
Figure 3.15
). Drainage from the soil zone was
calculated on a daily basis (
Figure 3.16
) for the
entire watershed. Drainage from each HRU was
transported to underlying MODFLOW-2005 cells
by using the kinematic wave approach. A com-
bined model allows dynamic feedback among
the aquifer, soil zone, and surface-water bodies.
Water can be transported upward or downward
on the basis of calculated water levels. This
feature is important for this example because
much of the water that recharges the aquifer is
returned to the surface as groundwater levels
rise, generally in late spring and early summer
(
Figure 3.16
).
Combined watershed/groundwater-flow mod-
els such as GSFLOW are useful tools for esti-
mating groundwater recharge. The integrated
approach considers the entire hydrology of a
watershed/aquifer system; calculated recharge
rates may vary in both space and time. These
models provide unprecedented opportunities for
evaluating the sensitivity of recharge rates to cli-
mate, land use, water use, and other natural and
anthropogenic factors. The models are also use-
ful for predicting how future changes in any of
these factors may affect recharge processes. The
major drawback of using these models is that
they are difficult to apply. Most model users will
require extensive training.
