362 fry. SEDIMENTATION IN RESERVOIRS [Ch. 20 



point of seriously impaired usefulness, future generations may find it 

 necessary to remove portions of the existing dams and permit sedi- 

 ment to pass on downstream over a period of, perhaps, several years. 

 After the desilting has taken place, the portion of the structure could 

 be replaced and the reservoir restored to something like its original 

 life. 



FUTURE RESEARCH NEEDED 



Much additional research is needed in the field of sedimentation in 

 its application to reservoirs. Probably most of this will be done by 

 federal agencies, which are most concerned with sedimentation in 

 reservoirs built by the various agencies. There is also a wide field 

 for research investigations by non-federal agencies in connection 

 with such matters as determination of the laws of sediment trans- 

 portation and particle-size determination. 



Samplers for suspended sediment have been developed to an ad- 

 vanced stage, but satisfactory methods and equipment for bed-load 

 measurements are still a fertile field for exploration. 



In reservoir-sedimentation surveys, there is opportunity for further 

 improvement in echo-sounding equipment. In this field, probably the 

 research most needed is for the development of practical and economi- 

 cally feasible methods for determining horizontal positions of reser- 

 voir soundings by electronic methods. 



Determination of the density of deposited sediments and the laws 

 of consolidation of materials under conditions that exist in reservoirs 

 offer opportunity for research, because the density and consolidation 

 of material in a reservoir are so important in determining the volume 

 that will be occupied by sediment. Improved equipment is needed 

 to sample deposited sediments satisfactorily. Such equipment should 

 be capable of obtaining samples through 20 or more feet of sediment 

 under a depth of water of perhaps as much as 50 to 100 feet. 



REFERENCES 



Bell, Hugh Stevens (1942). Stratified flow in reservoirs and its use in prevention 



of silting: U. S. Dept. Agr., Misc. Pub. 491, 46 pages. 

 Churchill, M. A. (1948). Discussion of paper, "Analysis and use of sedimentation 



data": Proceedings of Federal Inter-Agency Sedimentation Conference, Denver, 



Colo., May 6-8, 1947, U. S. Bureau of Reclamation, Washington, D. C, pp. 



139-140. 

 Eakin, Henry M., and Brown, Carl B. (1939). Silting of reservoirs: U. S. Dept. 



Agr. Tech. Bull. 524, h68 pages. 



