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Show without Federal assistance. Average annual assist- ance offered under this program is approximately $3,780,000. Much of the job remains to be done. Al- though a start has been made, the conservation machinery is slow in motion or absent in critical sections of the basin. As it takes time for con- servation measures to reach maximum effectiveness, it is too much to expect that damages from a cen- tury of misuse can be repaired in a year or two by the most complete application of specified measures. Building back the productive capacity of the basin calls for thrift, patience, administrative responsi- bility, and faith in the future of a rehabilitated basin. It also calls for a real effort by Federal and State agencies and all others concerned to make the best use of the resources at hand. There has been an inclination on the part of some public agencies to wait for added money rather than use fully the powers already conferred upon them by legislation. The most effective method known to rehabilitate the grazing areas requires that grazing use and man- agement be restricted to obtain natural recovery. To date, practical methods of rehabilitation by seeding have not been developed. Program for the immediate future.-Some addi- tions to going programs are in prospect. A new watershed survey has been made by the Department of Agriculture of the entire Pecos River Basin regarding runoff retardation and sedi- ment control in aid of flood control. A similar survey report is being made for the area of the Rio Grande Basin between headwaters of the Rio Chama and Fort Quitman, Tex. These reports present a generalized picture of watershed condi- tions which, affect flood water and sediment, water- shed measures which will improve these conditions, and their estimated cost to Government and to private landowners. These studies cover all water- shed lands regardless of ownership or administra- tion. All public land-administering agencies and others interested in these watersheds have contrib- uted to the basic material, and have participated in the recommendations for watershed treatment. A large part of this program would consist of accelerating present agricultural and management programs which reduce flood water and sediment. They would be supplemented by minor structures to assist in establishing and maintaining an ade- quate vegetal cover and controlling sediment where the erosion, cycle has progressed too far to be ar- rested by vegetation alone. Each land-administering agency will carry out this work on lands under its jurisdiction, while the Department of Agriculture will be responsible for carrying out work on private lands in cooperation with owners or occupiers. Main Stream Control Works Existing projects.-There are no main stream control works designed primarily to control sedi- ments. Reservoirs trap and reduce the sediment load carried by the stream below the dam. Bene- ficial effect of reservoirs is greatly reduced in three ways. A stream issuing from a reservoir, free of sediment, picks up another load if its velocity permits and the sediments are available; a delta at the head of a reservoir increases aggrada- tion of a stream channel above a dam; and diver- sions of a stream to irrigated land decrease capacity to move sediments in the channel. Main stream works will be warranted more and more to control and limit movement of suspended and bed loads of sediments down river channels. Local sediment problems may be shifted by such works from one place to another but the sediment problems of the basin will not be reduced adequately until sediment-producing erosion is controlled at its source on watershed lands. Projects under construction and authorized.- Two projects which have sediment detention as one of their primary purposes are included in the au- thorized plan for the Middle Rio Grande Basin. Jemez Canyon Dam on Jemez Creek, now under construction, will provide 90,000 acre-feet of stor- age for sediment and 30,000 acre-feet for flood con- trol. The authorized Chamita Dam would provide 180,000 acre-feet of storage for sediment and 508,- 000 acre-feet for flood control. A major purpose of these structures as a part of the plan of flood con- trol is to reverse the trend of aggradation of stream beds. It has not been established how long it will take for these structures to accomplish this purpose, as the behavior of streams heavily loaded with sedi- ments is unpredictable. Program for future construction.-The Chiflo Project, recommended by the Corps of Engineers primarily for flood control, would provide 30,000 acre-feet of sediment storage. Five other multiple- purpose reservoirs, in which a primary function is to trap sediment, are being studied for the upper Rio Grande and Pecos River Basins. Flood control dams will store the present sedi- ment load for about 50 years, after which time sedi- ment will encroach on flood storage capacity. A 302 |
