Environmental Engineering Reference
In-Depth Information
Figure 3.17
Average annual
recharge in Minnesota (1971-
2000) (Lorenz and Delin,
2007
).
0
20
40
60
80 MILES
0 20 40 60 80 KILOMETERS
Recharge in millimeters
per year
0 to 100
Water
100 to 200
200 to 300
>
300
Unclassifiable
recharge map is useful in identifying regional
trends, and, as would be expected, the pat-
tern of recharge is similar to that of precipi-
tation, increasing from west to east across the
state. Some care should be taken in assessing
the absolute accuracy of estimates displayed
in the map. Uncertainty in the recharge esti-
mates arises from the fact that Equation (
3.13
)
is derived on the basis of estimates of recharge
rather than actual values of recharge; the
accuracy of those estimates is unknown. An
additional source of uncertainty is the upscal-
ing process whereby Equation (
3.13
) is applied
to areas outside of the 38 gauged watersheds.
There is also the question as to whether the
recession-curve displacement method provides
an estimate of actual recharge or of base flow
(Sections
4.1.2
and
4.5.2
).
