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Thesis (Ph. D. - Political Science)--University of Arizona, 1986. / Includes bibliographical references (leaves 313-330).

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This report describes the development and application of a spreadsheet -based model of the water budget and water management systems of the Upper San Pedro River Basin in southeastern Arizona. The model has been given the name, WATERBUD.

The investigation reported in this dissertation is a portion of a larger effort to determine how allocation of water resources affects economic and social development in an arid environment. The study focuses on irrigated crop agriculture in Western Yuma County, Arizona, where irrigation water supplies are obtained from diversions from the Colorado River. Irrigated agriculture accounts for nearly 95 percent of total water use in this area. Linear programming techniques are used to determine optimum farm output and resource use patterns for five different farm models representing different farm size groups. The farm models were synthesized from data collected in a survey of 102 farms within the study area in 1964. This sample represented about one-fourth of the total universe. The linear programming analysis proceeds in four phases. In the first phase solutions are obtained for each model under the assumption that the size structure of agricultural firms and the resource base is fixed at current levels. In the second phase additional activities are added to permit land acquisition or disposal by each model farm. In the third phase the original formulation is modified to permit reclamation of new lands under the assumption that existing water rights will be perfected. The fourth phase combines the individual models analyzed in phase two into an integrated general model in which resource disposals by one farm size model must be balanced by acquisition in another. The final stage of the analysis includes estimates of crop output, and resource use under conditions specified in each phase. The marginal value product of selected resources is discussed and demand schedule for additional water is estimated. Land transfer price ranges are also discussed.

The elevated Kaibab plateau in northern Arizona has an area of 88 0 square miles and lies adjacent to the Grand Canyon of the Colorado river. It is composed of a sequence of lithified Paleozoic rocks that are approximately 4000 feet thick and consist of marine sediments that contain very little permeability. The ground water system of the plateau has two principal components: 1) circulation through unfractured stratified rocks that range up to a few tens of miles wide and 2) fault controlled drains. In unfractured zones, most of the ground water circulation takes place in the upper 900 feet of the section. The water drains laterally through these rocks toward fault zones or seep faces along the canyon walls. Approximately 40 percent of the plateau surface (330 square miles) drains to canyon seeps. Fault zones provide laterally and vertically continuous large capacity conduits through the plateau. These function as drains for the ground water system as well as floodways for storm pulses that enter the faults directly from the surface. Fracturing has controlled the development of extensive karst networks in limestones that lie near the base of the Paleozoic section. These systems drain to 10 groups of karst springs that discharge an average of approximately 100 cubic feet of water per second. The karst springs drain approximately 60 percent of the plateau surface (550 square miles). The springs in Tapeats amphitheater on the west side of the plateau discharge from the extensive West Kaibab fault zone and account for approximately 70 percent of the measurable water leaving the plateau. This group of three springs drains about 40 percent of the plateau surface (380 square miles). Development of ground water supplies does not appear to be economically tenable in the unfractured portions of the plateau because the permeabilities of the rocks are very small and the depth to the small quantities of available water exceed 500 feet. Production from the large fault controlled drainage networks is equally unattractive. Although the occurrence of water is certain, the large supplies are more than 2800 feet below the land surface and exist in finite channels along the fault zones. These would be difficult to penetrate with conventional drilling methods.

From Imperial Dam downstream, in addition to Mexico, the Colorado River supplies water to Arizona and California for predominantly agricultural use. In Arizona, the Colorado River is the major source of water supply to the various irrigation districts in the Yuma area. Due to legal constraints, the amount of Colorado River water available to the State of Arizona is limited. On the other hand, it was discovered that the amount of water applied to the soil in irrigation exceeds that amount needed for crop-growing. Two areas where the amount of water considerably exceeds the requirements, the mesa section of the Wellton-Mohawk Irrigation and Drainage District and the Yuma Mesa Irrigation and Drainage District, were studied in detail. The excess water applied on the mesa of the Wellton-Mohawk Irrigation and Drainage District flows into the Wellton-Mohawk Valley whence it is pumped into a conveyance channel and then discharged into the main channel of the Colorado River. This drain water has a very high salt content and therefore it adversely affects the quality of the river water. Since the drain water is discharged into the Colorado River above the point of diversion to Mexico and it is considered to be part of the Mexican water allotment, the quality of the Colorado River water has become a source of friction between the United States and the Republic of Mexico. The excess irrigation water from the Yuma Mesa Irrigation and Drainage District flows into the adjacent valleys as well as into uncultivated areas. In the adjacent valleys it is raising the water table and thus causing drainage problems. When it flows underground into the uncultivated lands, in large measure it constitutes a loss of water that otherwise could be put to beneficial use by Arizona. It is known that flood irrigation is not conducive to efficient application of water in the sandy soils that are predominant in these areas, and that the effects of this application of excess water are diverse and far-reaching. The change to sprinkler irrigation would be advantageous in many ways and beneficial to all concerned. The change to sprinkler irrigation on the mesa of the Wellton-Mohawk Irrigation and Drainage District would benefit both the farmers and the district financially. At the same time, it would decrease the salinity of the Colorado River water, thereby improving the quality of the water that Mexico receives and, consequently, the relations between the United States and the Republic of Mexico. In the Yuma Mesa Irrigation and Drainage District, the change in the method of irrigation would increase the amount of water available for use by the State of Arizona. Furthermore, it would alleviate the drainage problem of the adjacent valleys and would thereby decrease the amount of drain water flowing back into the channel of the Colorado River. In this district, such a change may entail a small added cost to the farmer. Alternatives for augmenting the flow of the Colorado River, such as importation of water from other basins, desalting sea water, phreatophyte eradication, and evaporation suppression, were found to be economically unfeasible at present or still in the experimental stages.