AZ vs. CA:24 California Exhibits, Vol. XXIV; Miscellaneous

page 175

PROBLEMS OF. IMPERIAL VALLEY AND VICINITY. 175 South of the Gunnison lie the headwaters of the San Juan, with a large but comparatively early run-off. To the east lies the Rio Grande, but no diversions have been proposed from it, nor is any such diversion believed feasible because of the extraordinary difficulties which will be encountered in getting water from the deep canyons of the San Juan. Moreover, the expense of reaching large areas of irrigable land along the Rio Grande from the Rio Grande River is almost prohibitive in itself. South from the San Juan, the Continental Divide is low and flat, precipitation is small, and stream discharge so erratic that trans-mountain diversions are not likely to be successful. On the west side of the Colorado Basin and in that portion of the divide between the Great Basin and the Colorado, which lies south of the Uinta Mountains, there are no areas of large precipitation such as are found on the eastern margin of the basin. Nevertheless, in the valleys of the Great Basin in Utah returns from irrigation are large and the divide offers no such obstacles to diversion as are found on the more precipitous and colder slopes of the Continental Divide. Hence some diversions have been made and as there has been opportunity to construct reservoirs on the Colorado Basin side, which go far to make such projects a success, the present diversion exceeds that to the east on the opposite side of the basin. However, it is believed that little opportunity exists for diversions additional to those now operating. In general, transmountain diversions to the east from the Grand River have been expensive and disappointing on their yield, but when large enough to warrant close observation and maintenance are quite successful. , No reservoir sites are. known on the headwTaters of the Grand, such as have made the Reclamation Service diversion from Strawberry River to Spanish Fork so successful in Utah, and such as have been constructed for diversion from the Virgin River in Utah. (Located, in secs. 19 and 20, T. 38 S., R. 14 W., Utah.) It is believed, however, by engineers conversant with* the situation that although the expense of constructing the diversions proposed as noted m the table will be heavy per unit of yield, yet, because their size will justify adequate maintenance, they can be successfully operated. In this report, only those listed are considered in water supply computations since data are not available concerning other projects which may have been proposed. On the following pages, tabular de'scriptions of existing and proposed diversions are given. It will be observed that proposed diversions from the Grand contemplate expensive tunnels and average 1,000 feet lower .than operating diversions, thereby giving much greater water opportunity.