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: 7
74 p. : ill., mapsView a full description of this report.
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computer was used to construct maps which reflect the
saturated thickness of the aquifer for those years
included in the study. These maps were then refined by
the computer to reflect the number of acres
corresponding to each range of saturated thickness. The
number of acres for each range was multiplied by the
saturated thickness in feet for that range and then by the
coefficient of storage (0.15 or 15 percent), to yield an
estimate of the volume of water in storage in each
saturated-thickness range. Totaling these volumes
produced an estimate of the volume of water in storage
in the county. The current (1974) and projected volume
estimates are shown in the following graph:12-
10-
O8-C
0
E
S
E
06
4-
2
0
' A c, 0b~ o 0 01toYear
1974
1980
1990
2000
2010
2020Acre -Feet
6,463, 000
5,716,000
4,657,000
3,772,000
3,049,000
2,462,000Estimated Volume of Water in Storage
Preparing a data base and writing the necessary
programs for the computer to use in constructing the
saturated-thickness maps and in making the necessary
calculations is time consuming; however, once the data
base is prepared and programs written, the computer can
perform in a few hours calculations that would have
required many years of manual effort.
A generalized description of the methodology used
in mapping and in computing water volume follows: A
base map with a scale of 1 inch equals 2 miles was
selected to prepare data for computer processing. All
data points (observation wells) were plotted on these
base maps by hand and assigned identifying numbers. A
machine called a digitizer was then used to translate
these mapped location data (well locations, county
boundaries, etc.) into information processible by the
computer. To accomplish this, a latitude and longitude
coordinate was recorded on each base map as a central
reference point, and all data points and county
boundaries were then digitized; that is, measurements
were made by the digitizer to reference these data points
and boundaries to the initial latitude and longitude
coordinate. Then the digitized information was
processed by the computer and the maps were re-created
by a computer-driven plotter. The computer-plotted
image maps were ultimately checked against the
hand-constructed maps to verify that the data were
plotted accurately.The assignment of a unique number to each data
point (observation well) on the base maps made it
possible to machine process the data related to these
points and to plot these data back on the maps at the
proper location.
To compute the volume of water in storage, the
computer was instructed to subdivide the county into
units of approximately one-half mile square. The known
saturated-thickness values obtained from the data points
were filled into the squares in which the data points
were located. Based on these known values, the
computer filled in a weighted-average value for each
remaining square, taking into consideration all known
values within a radius of 7 miles. After this step was
completed, the computer then counted the numbers of
squares having equal values, thus obtaining the
approximate area in square miles (later converted to
acres) corresponding to each range of saturated
thickness. As previously stated, the number of acres in
each 25-foot range of saturated thickness was multiplied
by the corresponding saturated-thickness value and the
storage coefficient (0.15 or 15 percent), to obtain the
approximate volume of water in acre-feet in that
saturated-thickness range.
Although the calculations were made by the
computer from information stored in its image field, the
data in the image field were printed out in the form of
contoured saturated-thickness maps, which are
reproduced in this report. Facing each
saturated-thickness map in the report is a corresponding
tabulation of the approximate volume of water in
storage.
Calculating Pumpage
Estimates of current pumpage were obtained in
this study by calculating the storage capacity of the
dewatered section of the Ogallala aquifer as reflected in
changes in the annual depth-to-water measurements
made in the water level observation wells. Factors for
natural recharge and irrigation recirculation were then
added to these volumetric figures to obtain more
realistic pumpage estimates.
The step-by-step procedure involved in making
pumpage estimates is similar to the procedures used in
calculating the estimates of volume of water in storage;
therefore, a more general explanation follows.
Change in water level (decline) maps for the
aquifer were made by the computer for the years
considered. From these maps, the volume of desaturated
material was multiplied by the number of acres-7-
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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/m1/15/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.