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

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The aquifer permeability (K) and fillable void (V) used in all evaluations
were based on a single pumping test at each pond. The observation wells used to
monitor the ground water were also used in this test. The pumped well was
rotary dJ:il1ed with mud to a diameter of 6 inches, cased, and gravel packed.
Both were fully penetJ:ating because a concrete plug was poured at a depth of 41
feet at pond No.1.

Other Parameters

The recharge rate (i) was taken as the rate that water enters the surface
of the pond. Theoretically, i is considered independent of time since start of
operation and with the water entering the water table uniformly over the project
plot area. For these ponds, this was not the case because the movement of air
beneath the pond produced considerable curvature in the advancing wet front and
measurable changes in vadose zone storage after recharge commenced (2).
The instant that recharge commenced (t = 0) was best estimated from the po-
sition of the wet front as determined by neutron probe measurements (2). The
initial position of the water table was best determined from well observations
pJ:ior to flooding, corrected for barometric fluctuations.

EXPERIMENTAL RESULTS

Rising Hydrograph at Center of Mound

Glovers treated theoretically the water table case of the rise of the cen-
ter of the mound beneath both square and round spreading areas subject to con-
tinuous discharge and found that both geometric shapes provide nearly identical
hydrographs. The circular case is described by his equation 16 as follows:

r W J
-u -u
ho = Rt l-e 1+U1 f ~ dU
U1 U
where
a2
U1 = 4cit
R = i t2:0 from D;::r;::a
- at
V

(1)

(2)

(3)

and

ho = rise in water table above initial static level
t = elapsed time afteJ: recharge starts
a = equivalent radius of the recharge area
i = uniform continuous recharge rate
a = KD/V = (the aquifer constant)

SSee footnote 2.

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