PROJ00132

• Contract/PO #: FS0014X
• Contractor Name: Southern High Plains Ground Water Management District
• Contract Type: Loan
• Water District: 0
• County: Prowers
• Loan Projects - Doc Type: Feasibility Study

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5.2 ESTIMATED WATER USE
The ability to determine the amount of water actually being withdrawn from the aquifers
depends upon either direct measurement or approximation. Examples of direct measurement
include flow data obtained directly from wells that are either equipped with totalizing flow meters
or hour meters if the rate of discharge of the well is already known. The approximation method
utilizes equations and climatological data to estimate the volume of water required. These two
methods can be used together to provide accurate estimates of the overall pumpage for an
area. One method of estimating water demand is based upon the Blaney-Criddle method with
climatological input data from local sites.

The source of the crop coefficients used in the Blaney-Criddle formula are from the "Irrigation
Water Requirement Technical Release No. 21" developed by the USDA's Soil Conservation
Service. Two sites within the District, Springfield and Walsh, which have climatological data,
were selected for this analysis. Springfield was selected because it has a longer period of data
and associated climatological averages than Walsh. Walsh was selected because it is
approximately twenty miles east of Springfield making it more centrally located and more nearly
the same elevation within the irrigated area of the District. In addition, Springfield is
approximately 600 feet higher in elevation than Walsh.

The estimated monthly and seasonal irrigation requirements per acre using the Blaney-Criddle
method were multiplied by the number of acres of the four major crops being irrigated to
estimate the peak monthly demand and seasonal demand for the respective irrigation water
requirements for the four major crops in the district. The results of these calculations are
presented in Table 5-2. This analysis shows that there would be in excess of 220,000 acre-feet
of water withdrawn annually to the approximately 128,800 acres of the four major irrigated crops
(corn, wheat, sorghum, and alfalfa) in the basin. This volume of water was estimated by
inserting the weather data from Springfield, Colorado into the Blaney-Criddle method. An
irrigation efficiency of 85 percent was assumed for these calculations. This level of irrigation
efficiency reflects the significant number of center-pivots equipped with drop nozzles that are
present in the district.

For comparison purposes, 1999 weather data from the Walsh weather station was used to
estimate the volume ground water pumped in 1999. These volumes for each crop type are
presented in Table 5-3. The total annual volume of water estimated to be withdrawn would
increase to nearly 227,000 acre-feet using the Walsh climatological data. Similarly, the 1999
weather data for Springfield was used to estimate the ground water pumpage volume in 1999.
These volumes for each crop type are presented in Table 5-4. The total annual volume was

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