Alternative routes

Four alternative routes for conveyance of desalted sea water to the Colorado River were examined for purposes of comparison to the base plan. For each alternative route, costs were estimated for the provision of 2 m.a.f. and 2.5 m.a.f. of augmentation supplies. (See map of alternative routes.)

Those alternative plans which involve the delivery of desalted water into the Colorado River downstream of Hoover Dam (plans A, B, and D) would not have the use of storage capacity of Lake Mead for regulation. As a result, preliminary studies indicate that these plans would require additional regulatory storage as a feature of the augmentation plan.

Such storage near the terminal point of the conveyance works would also provide an opportunity to mix the very high quality desalted water with the natural river water. It appears that provisions for adequate mixing will be es sential to optimize the benefit from use of the desalted water to reduce the river's salinity, as well as to avoid the problems associated with delivering water of widely varying quality to users.

Cost estimates for plans A, B, and D include the costs of a regulatory reservoir on the Bill Williams River arm of Lake Havasu located approximately 2 miles upstream from Parker Dam. The Bill Williams Reservoir would have a storage capacity of about 800,000 acre-feet, and the estimates include provisions for pumping from Lake Havasu into the reservoir. It would provide sufficient storage capacity to accommodate hydraulic mixing as well as regulatory storage to maintain efficient operation of the river.

The estimates for plans C and D incorporate dual-purpose nuclear desalting complexes situated at El Golfo de Santa Clara on the Gulf of California. As discussed later, siting of the plants in Mexico would involve international agreements. A joint study group formed by the Governments of the United States of America and Mexico and the International Atomic Energy Agency is currently conducting an assessment which will serve to define these considerations. Summary tabulations of the costs and physical features of the alternative routes follow:

2 Includes fuel costs, interim replacements, and sinking fund to rebuild at the end of 30-year service life.

Includes allocated power costs for project pumping.

* Includes fuel costs, interim replacements, and sinking fund to rebuild at the end of 30-year service life.

CONSIDERATIONS FOR FEASIBILITY STUDIES

The objective of this study was to explore, based upon reconnaissance level data, the possibilities of augmenting the water supply of the Colorado River by desalting of sea water. The plan presented herein has been selected in order to demonstrate the various factors involved in the concept of augmentation by desalting of sea water without introducing unnecessary complications. In the course of study, a number of potential alternative or modified courses of action were taken into consideration. Because of limitations on the time and scope of the study, it was not possible to explore in detail all of the potential opportunities to improve the plan. A number of these possibilities appear to be of significant potential advantage, however, and should be considered in detail when feasibility studies are undertaken. The following discussion concerns the most important of these possibilities.

Coordination with Mexico-United States of America desalting proposal studies A joint study group has been formed by the Government of Mexico, the Government of the United States of America, and the International Atomic Energy Agency to make a preliminary assessment of the technical and economic practicability of a dual-purpose nuclear power and desalting plant which would serve the general areas of California, Arizona, Baja California, and Sonora. The work on this assessment is presently under way.

It is certain that long-range provisions for additional augmentation of the Colorado River will be necessary to support the continued economic and sociological development of the Pacific Southwest. The assessment being made by the joint study group is giving consideration to providing for such long-range needs.

If agreement is reached among the parties and plans to proceed with this joint venture materialize, an opportunity might exist to obtain the augmentation water from this source at a significant saving, particularly in conveyance costs. Consolidation of these two proposals would impart the advantages of financing

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associated with the augmentation to a portion of the joint venture, and important advantages might be provided the augmentation effort by plant siting în Mexico Because of the obvious uncertainties of international agreements and timing associated with siting of the plant in Mexico, this reconnaissance report has been based upon a plan which is located entirely within the United States. If feasibility studies are undertaken, however, further attention should be givet to the progress of the study group's efforts and economie analyses made of th alternative of utilizing the joint venture as a source of augmentation water. National Water Commission

Congressional action is well advanced on pending legislation to establish National Water Commission. If established, it is anticipated that the commissier will address itself to the problems of water supply in the Pacific Southwest at 23 early date. Among the factors which should be considered by the commission is the practicability of augmenting the Colorado River by desalting of sea water To meet the objectives outlined in this report, it will not be necessary to initiate construction of desalting facilities until after 1980. The National Water Commis sion's recommendations will be available well in advance of the need to make i final decision to proceed with construction.

Need for additional augumentation

This reconnaissance study has been directed toward the provision of sufficient water to prevent shortages in the 7.5 m.a.f. of annual consumptive use appor tioned among the State of the Lower Colorado River Basin. The provision of this quantity of water would, of course, not supply adequately the potential uses of the Pacific Southwest. California uses from the river presently exceed 50 m.a.f. annually and would, with this augmentation in effect, be reduced to an assured 4.4 m.a.f. Estimates of Arizona's present ground-water overdraft made for earlier reports are 2.2 m.a.f. annually as compared to about 1.5 m.a.f. which would be supplied from the Central Arizona Project. Nevada's allocation has been estimated to be adequate to provide for municipal and industrial growth of the Las Vegas metropolitan area until 2020, but population growth is exceeding the projections annually in this area. One potential source for provision of water would be by desalting, as is being studied by the joint committee discussed above. The ability to provide staged construction of desalting facilities has the advantages of flexibility in timing capacity to meet needs, spreading the time of construction investment, and maximizing the use of advancing technology. Future studies of desalting facilities should include consideration of additions: capacity for long-range needs. If such capacity can be shown to be desirable, plans should include provisions which would facilitate future stages.

The Upper Basin has committed the major portion of its available water supply. Large population centers within and adjacent to the Upper Basin will remain dependent on the Colorado River for the development of increased sup plies of municipal water. Mineral resources of phosphates, oil and gas, coal. trona, uranium, and oil shale exist extensively in the Upper Basin and would depend on a supply of additional water for development. Agricultural oppor tunities also exist which could use additional water.

Potential pumped storage

In the course of the reanalysis of the Central Arizona Project, which was performed in late 1966, and other reconnaissance-grade investigations. the Bureau of Reclamation has made preliminary examinations of a number of potential pumped storage, hydroelectric plants in Arizona. The plan which appeared most favorable, based upon available data, was the Mohave pumped storage plan which is located in Arizona adjacent to Lake Mohave about 21 river miles downstream from Hoover Dam.

The existing Lake Mohave, the reservoir formed by Davis Dam, would serve as the lower reservoir for the installation. Low cost thermal electric power from plants of power systems in the Southwest would be used at times of low power demand to pump water, using reversible pump-generators, to an upper reser voir. The 49,000-acre-foot upper reservoir would be formed by excavation and damming of a natural depression on Malpais Mesa almost 1,400 feet above Laks Mohave.

During periods of peak power demand or at times of sudden loads on the integrated power systems, water would be released from the upper reservat back into Lake Mohave, providing a source of quickly available, high value peaking power.