Analytical Study of the Ogallala Aquifer in Bailey County, Texas: Projections of Saturated Thickness, Volume of Water in Storage, Pumpage Rates, Pumping Lifts, and Well Yields Page: 5
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determined or estimated, and those needed to provide
spaced data coverage in the county. Locations of the
wells that were selected and used for control are shown
on the various maps in this report.
Projecting the Depletion
of Saturated Thickness
The water-use patterns between 1960 and 1972 as
reflected in the changes in water levels in wells measured
in the High Plains of Texas were used as the principal
data source for developing an aquifer depletion schedule.
The depletion schedule generally reflects average
precipitation and precipitation distribution in the area
for the duration of the study period. Additionally, in
developing and applying the depletion schedule,
adjustments through time were made to reflect the
effects of depletion of the aquifer on its ability to yield
water. That is, as the aquifer's saturated thickness
decreases, its ability to yield water to wells is reduced,
the well yields decline, less water is pumped, and there
results a lessened rate of further aquifer depletion.
The aquifer's hydraulics are such that if a well
penetrates the total saturated section and the pump is
sized to produce the maximum the aquifer will yield, the
well yield will decline at a disproportionately greater
rate than the reduction in saturated thickness. Actually,
the remaining well yield expressed as a percentage of
former yield will be only about half of the remaining
saturated thickness expressed as a percentage of former
thickness. For example, a well with 80 feet of saturated
section and a maximum yield of 800 gpm (gallons per
minute) will probably yield only 200 gpm when the
saturated section is reduced to 40 feet.
The depletion schedule for Bailey and surrounding
counties was developed in the following manner:
1. The records for all water level observation
wells for the years 1960 through 1972 in
Bailey, Lamb, Hale, Floyd, Crosby, and
Dickens Counties were separated from the
master file. These counties have similar soil
types, cropping patterns, depths to water,
saturated thickness, and climatic conditions.
2. These well records were then sorted into
groups according to the saturated thickness
in each well as of 1966 (the middle year).
Each group included records of all wells in a
20-foot range of saturated thickness.
(Ranges are shown in the tabulation below.)
3. The average decline in water level wasand these decline values were adjusted to
remove the effects of each year's deviation
from long-term average precipitation.
4. The average annual decline in water level for
the total period (1960-72) was calculated for
each well group, incorporating the
adjustments for departure from average
precipitation.
From the foregoing procedure, the following
depletion schedule was developed:RANGE OF
SATURATED THICKNESS
(feet)
Oto 20
2O to 40
40to 60
60Oto 80
80 to 100
100 to 120
120 to 140
140 to 160
160 to 180
180 to 200
200 to 220
220 to 240
240 to 260
260 to 280AVERAGE ANNUAL
WATER-LEVEL
DECLINE, 1960-72
(feet)
0.35
.75
.95
1.45
1.67
2.08
2.05
2.99
3.00
3.40
3.70
3.67
3.60
4.08Based on this depletion schedule, a computer
program was written to calculate future saturated
thickness at individual well sites. The following problem
is presented to show the computational procedures used.
Problem: A well has a saturated thickness of 110
feet in 1974 and one wants to project what the
saturated thickness will be in this well for every
year to the year 2020.
Factors: 1. The beginning saturated
thickness is 110 feet in 1974.
2. The average decline rate is 2.08
feet per year for wells with
saturated sections of 100 to 120
feet.
3. The average decline rate is 1.67
feet per year for wells with
saturated sections of 80 to 100
feet.
4. The average decline rate is 1.45
feet per year for wells with
saturated sections of 60 to 80
feet.calculated for each year for each well group,
-5-
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Wyatt, A. Wayne; Bell, Ann E. & Morrison, Shelly. Analytical Study of the Ogallala Aquifer in Bailey County, Texas: Projections of Saturated Thickness, Volume of Water in Storage, Pumpage Rates, Pumping Lifts, and Well Yields, report, June 1976; Austin, Texas. (https://texashistory.unt.edu/ark:/67531/metapth1203972/m1/13/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.