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Show for sealing- canals on irrigation projects, as for the Glendo, Wyo., project where concern has been ex- pressed that sufficient silt will not be available to prevent serious canal leakage now eliminated by silt sealing. Examples of the advantages to be gained by using sediment are to be found at the main stem reser- voirs under construction and proposed for the Mis- souri River. The clean water discharged from these reservoirs will regain a sediment load by de- grading the channel below the dam. This process could become a serious liability. However, sedi- ment engineering procedures are being utilized to derive some benefits by using the lowered tail water levels to gain additional power head. Plans also are being worked out to control natural degrada- tion tendencies of the Missouri River and utilize them in tlie establishment and maintenance of navigation channels. At present, natural sediment loads of the river are being used to contract and stabilize the river and improve its channel for navigation. Present approaches to sediment control.-Basic data on sedimentation are among the least adequate elements in planning land and water developments. An over-all outline of the problem and a statistical measure of its magnitude was undertaken in the "308 Report" on the Missouri Basin.20 Further investigation was initiated in 1938 and has been carried on in an expanding program. However, much remains to be done. Approximately 150 sediment stations are oper- ated to provide data on the source, nature, and distribution of sediment. Major areas of sediment production are being studied to determine the pos- sibilities of reducing erosion, and reservoirs are being designed with sufficient capacity to store in- flowing sediment without interfering with normal operation for 100 years or more. A continuous program of research into the funda- mentals of sediment transportation is being prose- cuted in order to determine in advance how various forms of aggradation, degradation, and other chan- nel variations will occur, the extent to which they may go, methods of controlling them, and methods of putting th em to use. Approximately 75 men, in- cluding field sampling personnel and laboratory personnel, are continuously engaged in the investi- gation; and a group of expert consultants are retained for individual and group discussion and advice. Hydraulic laboratory investigations into 'H. Doc. 238, 73d Gong., 2d sess. (1935). the basic laws of sediment transport are being car- ried on among other places at the University of California and the University of Minnesota, and detailed observations of the hydraulic character- istics and sediment load of reaches of the Missouri River are being made. The total expenditures on sediment investigations in the Missouri River Basin are approximately $500,000 annually. About half of this amount is from the Corps of Engineers' funds, and the re- mainder is contributed by the Bureau of Reclama- tion, the Geological Survey, the Soil Conservation Service, and the Forest Service. Other approaches are being suggested in the Department of Agriculture program, as outlined in House Document 373 (81st Cong., 1st sess.), where- by watershed management may be able to reduce sediment from cultivated land, forest, and range. Future approaches to sediment use.-When and as information develops through experience and re- search, procedures can be planned to salvage the values now wasted to the ocean. This salvage is accomplished in nature by the recurrent floods depositing the sediments on the bottom lands throughout the lower Missouri and the Mississippi. It may well be possible to flood segments of the river bottom lands artificially under proper control, as is done in flood irrigation, drawing the water off leaving the sediment and salts. This is the "polder" system. The possibility of carrying silt through the res- ervoirs in density currents with properly controlled outlets in the dams, so as to deposit it at down- stream points of use, should be examined. Conclusions Sedimentation is a serious problem in the effective use of the Missouri River and its tributaries. In spite of past research, basic data still are lacking for determining the most effective physical solutions to sedimentation problems. It is essential that re- search and experimentation in erosion control be accelerated. It is also necessary to expedite operat- ing programs in land management and the control of erosion and sedimentation as fast as is consistent with existing technical knowledge. Control of sedi- ment near its point of origin on tributaries offers promise of cleaner water; in some situations the use of main channel works may make possible the bene- ficial use of sediments. The use of dead storage in reservoirs is, of course, the principal present means of disposing of sedi- 220 |