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Show and channels of navigation projects because of the in- creasing draft of boats and barges. All of the hydroelectric projects investigated were ade- quately serving the purpose for which they were designed. In some instances it has proven necessary to make modifi- cations of the project structures in order to improve their safety. The Extent to Which Projects Would Have Been Modified If More Adequate Data Had Been Available Many modifications have been made in existing projects since the date of their construction due to increased knowl- edge and more technical data. However, probably no project will ever be built that at some future time cannot be improved, upon. Experience has shown that in the development of any project it is essential to have adequate data on all factors which enter in the design or may affect the operation and maintenance of the project. In practically every project for water resource development it is essential to take into account not only the water but also the land. It is im- possible to leave the soil out of consideration in any irriga- tion or drainage project. Sedimentation affects to a greater or less degree every navigation and reservoir project. Many older projects would have been designed differ- ently if they were to be constructed today because of the increase in data and knowledge gained since the time of their construction. The outlet works of Grand Coulee Dam are to be modified so as to permit regulation for flood control. Such use was impracticable without the large additional flood control storage reservoirs recently added to the basin plan as a result of developments sub- sequent to construction of the dam. Grand Coulee also might have had provision built in it for more power units to provide for the use of upstream storage that may be created. Boaineville Dam might have had additional initial provision for the installation of future power units as additional stream flow is created by storage in upstream reservoirs. The navigation locks at Bonneville might have been larger-at least as large as those now being built at McNary----had there been knowledge of the changes in type of transportation required on the Columbia. As Arrowrock Dam the facing concrete did not with- stand the elements and has had to be replaced. Similar conditions exist at several privately constructed projects. Studies of concrete in these dams have developed new knowledge, a.nd have resulted in greatly improved con- crete for all types of construction. The outlet tunnel and gates at Shoshone Dam at the time of installation represented an experiment in opera- tion under a head much higher than those on which ex- perience had been obtained. Experience in the design and operation of these features has made it possible to design comparable features with assurance. Much new data are obtai ned from life-sized models. Even projects constructed in recent years would be slightly different had more data been available. At the Knightville Dam in Massachusetts the present hydrologic criteria would call for a somewhat larger spillway ca- pacity. With present knowledge of flood magnitudes the flood control storage would be at least 6 inches and preferably 7 or 8 inches of runoff from the watershed rather than the 5.6 inches for which the dam was planned, and if multipurposes were considered the Knightville Dam might have been designed for 12-inch runoff. These possible alterations indicate changes due to more com- plete knowledge, to improved criteria, and to a broader approach. Even though many of the older projects, both Federal and private have been a success, they have been in many instances based on inadequate basic data. The Shoshone project was based on 3 years of stream flow record, but the structures would not have been materially altered had there been a longer record. There might have been more spillway capacity according to present standards but the spillway has successfully passed all floods for more than 40 years. By contrast, the record of approximately 30 years used in planning the San Carlos reservoir em- braced years of runoff so much higher than has been experienced since that the water supply has been insuffi- cient for the irrigation contemplated. Whereas runoff exceeded the mean during 15 of the 30 years prior to con- struction, it has exceeded the mean during only 3 of the 22 years since construction. A great many private projects have failed due to lack of knowledge of soils, amount of water available, the floods to be expected, and present engineering techniques which have been developed since their construction. The St. Francis Dam in California failed due to lack of knowledge of the bearing capacity of the foundation rock. The Florida-Everglades drainage venture failed due to a num- ber of reasons such as the lack of adequate data, the volume of water to be handled, a lack of knowledge of characteristics of peat soils, and overspeculation. Where experience was lacking, such as in the irrigation of alkali or gumbo soils, many irrigation districts have had trouble, such as the Frannie unit of the Shoshone project and the Belle Fourche project. Many large areas in bogs or swamps in the upper Mississippi Basin were drained thus destroying a wildlife habitat before knowledge had developed concerning the best utilization of such land. Eagle Lake in California was drained through a tunnel and an agricultural economy was developed by private enterprise only to find that the tunnel lost a large percent- age of the water necessary for irrigation, and the water supply itself was insufficient. Thus an existing economy developed over a period of years was lost. When the Hastings Dam was built on the Mississippi River below St. Paul, changing the river from a fast moving one to a sluggish stream, the pollution load became serious as the average dissolved oxygen content reduced from 3.4 parts per million to 2.1. Construction of additional storage facilities to supple- ment water supplies originally provided has been necessary on many irrigation projects. Many causes are involved. Among them are: Overexpansion of irrigation facilities resulting from many diversions of stream flow; the occur- rence of increasingly severe periodic shortages in a gen- erally declining cycle of runoff; and the intensification of agriculture with resulting inability to withstand periodic water shortages without great loss. 404 |