WSP06416

• File Number: 8027
• Description: Section D General Correspondence - Federal Agencies - USDA - Agricultural Research-Service
• State: CO
• Basin: Statewide
• Date: 8/1/1975
• Author: USDA
• Title: Field Observations of Transient Ground Water Mounds Produced by Artificial Recharge into an Unconfined Aquifer
• Water Supply Pro - Doc Type: Report/Study

OD077"

~~~~

t~~

in which

K = hydraulic conductivity or aquifer permeability
V = void ratio or fillable void
D = saturated thickness'of aquifer

The integral in equation I is the exponential integral and has been evaluated by
Jahnke (15).
Figure 7 shows the agreement of these data at the center of the mound with
that observed during the test. If D = 75 feet is used in the theoretical eva-
luation of pond No.1, a drastic deviation is apparent (fig. 7A). The rise
evident in the observed data prior to recharge (t = 0) has been explained as
the localized response at the observation wells to the air pressure beneath the
wet front (2). The deviation from theory shortly after t = 0 can be attributed
to two possible sources: the absence of instantaneous uniform recharge, R ~ i/V
in equation 3,and the absence of the theory's consideration of vertical flow.
The latter would be most significant when the mound is most rapidly rising and
small in lateral extent. The deviation as t gets larger, particularly for pond
No.2 (fig. 7B), could be due to the increase in D as the mound J:ises or the
increase in V as most of the storage change shifts to outside of the projected
pond boundaries, as suggested by Bouwer (4). The storage capacities beneath and
outside of the projected pond area within the zone of rise of the water table
were estimated by nuclear scattering methods as indicated in the fi1lab1e void
values, I and 2 in table 1. While not directly comparative, the ratio of the
difference in the two values to that found by the pump test gives an index of
comparison between ponds. This ratio for pond No. I was 1.57 and No.2, 5.36.
As the hydrograph divergence is most apparent in pond No.1, it would seem that
the relatively large increase in D is the dominant influence rather than a shift
in storage from beneath outside the projected pond boundaries. Both these
changes, however, are undoubtedly responsible for quasi-equilibrium, which
is apparent in both hydrographs for large t.

Lateral Spreading of the Mound

G1over6 pJ:ovides a solution for the rise of a ground water mound due to
continuous recharge applied on a pond of width Wand length L. His equation
87 is as follows:

ft( 1 fU2 -u2 )
h=R - e au
o ;:rr u1

(2: /"e-U2au) an
;:rr U 3

(4)

where (x -;) Ix +;)
U U2
= =
1 14cx(t-n) 14cx(.t-n)
Iy - t) Iy-f) (5)
U = U" =
3 14cx(t-n) 14cx (t-n)
6See footnote 2.
8

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