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

00077'~

~i?

fg}

The influence of the lateral shift in storage outside the plot boundaries
is quite evident in the mound cJ:oss sections from pond No.2 (fig. SA and B).
Under the pond, the observed mound (identified as OB) is closely appJ:oximated
by the theory based on the minimum V obtained from the well test (see table 1).
The cross sections approach the theoretical cross section'outside the plot
associated with the maximum estimated V. The same is evident, but to a much
lesser extent, at pond No. 1 (fig. 8e) where the relative change in void is
smaller, and the overriding effect of D is the main influence. In both compar-
isons, however, an estimate of the void outside the pond boundary is needed if
an acceptable theoretical estimate of the ground water mound height is to be
obtained.

Falling Hydrograph

A modificiation of equation 1 can be used to estimate the fall of the cen-
ter of our observed ground water mound if we assume it to have a disk shape
with idealized J:adius (a) and initial height (H). Equation 1 takes the form:

ho = H (l_e-a2/4C!t) (6)

We can assume that H equals the final observed height of the rise of the mound.
From this value, we can approximate a fJ:om the total volume of water storage in
the mound when spreading ceased, plus the water that dJ:ained from the vadose
zone beneath the plot during the period of observed fall. This was accomplished
as follows:

Let V ' '" the total volume of water metered on the 2-acre ponds
a
(acre feet)
Vi' '" volume of wateJ: in vadose zone at the beginning of
spreading (acre feet)
Vr' '" volume of wateJ: in vadose zone at end of spreading
(acre feet)8
Vf' = volume of water in vadose zone at the end of observed
fall (acre feet)
V' effective mound volume (acre feet)

then the total volume of the mound plus that volume of water draining into it
during the fall is the effective mound volume:

V' = va' - (Vr' - Vi') + (vr' - Vf') = Va' - (Vf' - Vi')

where Vi', Vr', and Vf' were determined by averaging moisture profile observa-
tions in thJ:ee neutron access tubes in the pond area.
From Vi' (table 2) and the appropriate fil1ab1e void (V) (table 1), the
disk radius (a) at pond No. 1 equalled 894 feet and at pond No.2, 910 feet.
These values weJ:e used along with the aquifeJ: parameters from the pump test to
evaluate equations. The observed and theoretical hydrograph data were plotted
on figure 9. .The agJ:eement at pond No. 1 waS quite good with the apparent de-
viation being explained in part by the fact that the wetted depth (D = 16 feet)
used in the theoretical evaluation was low in comparison with the actual mound

8This expression would include the storage in the perched water table with
the vadose zone at pond No.2.

12

~f~J!~it

q<-~-~:~-.~-:~-,-...:)

'-'.'.

:.".;: .-.:
.,......

"""',"."
',".-.-"

'-J

-"....-...

-.-"

~> ?:-.->~:.
,'-;.' ~_.;.-..J

--..-,

,:<,:~,---,},:,-_::, -.

-'.':

'." .".

." -.- -.,
'-.". -.-.'.-

~l'i~_~<<\!f~~(~~~~t~~t~~i~i\~~~j>~