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U':' c- oo ... c 'The gradienr to the nonh into Im- peria/ Valley is mIlch greater than that 10 the south iJlto the gulj: and when the depression is filled there is no meaJ/s known which, at an)' cost within reason, can prevent the ri\'et from again flmving into ,he Imperial Valley. '771e dam propo.<.ed in 1Ms bill will catch and hold the sill. Most of rhe silr finding its way o11fo the delta is from and above the canyon sectioll, {[ no mller dams \Vere provided on the river, the one proposed in this bill IVould retain all of the silt finding its Iva)' illfo Ihe reservoir for a period of 300 years, and for morc than 100 years before ifS storage Capacif)' and usefulness would he seriously i11leljered wi,h. As other dams arc cOl/struc/('d 011 fhe river they will catch and rt~taiJ/ the silt, thereby fUl1her extending {he usefulness of Boulder Can- yon reservoir. " Reclamation engineers set aside ap- proximately 3 million acre-feet of Hoover Dam's rescrvoir capacity to sct- tie out sediment. Thc deep reservoir fonns a natura] trap. The river's flow slows as it entcrs the lake and thc sedi- ment, heavier than water, sinks to the bottom. The clean blue waters of Lake Mead testify that the reservoir's task of retaining silt is well performed. Glen Canyon Dam, 370 miles upstream from Hoover Dam, retains 75 percent of the silt that previously entercd Lake Mead, so thcrc is no likelihood of Lake Mead being filled with silt in the foreseeable future. Additional amounts of sediment are col- lected by other dams on Colorado River tributaries. Navigation on the Colorado Hoover Dam's completion also improved navigation on the Colorado River below Grand Canyon. Technically, the Colorado was always considered a navigable stream. In reality. navigating the river under natural condi- tions was extremely hazardous and 34 't"""'~~;. Lake Mead water is treared by the State of Nevada~' Alfred Merritt Smith plant, part of the Roberr B. Griffith Wafer Project, before if is delivered (() users in soufhern Nevada. decidedly impracticable. Now, craft rang- ing in size from small boats to luxurious cabin cruisers ply the waters of Lake Mead. Boating is also popular on Lakes Mohave (behind Davis Dam) and Havasu (behind Parker Dam) downstrcam from Hoover Dam, and along reaches of the river below these and other downstream control ancl diversion structures. A Nation's Playground The ultimate aim of Hoover Dam is, essentially, to promote the well-being and enjoyment of the American people. Lake Mead National Recreation Area, a na- tional playground, typifies this aim. The recreation area was fonned under a 1936 agreement between the Bureau of Reclamation and the National Park Serv- ice. On October 8, 1964, Congressional action gave the National Park Service direct administration of the area for recreational purposes. The Park. Service's efforts havc made this area one of the Nation's outstanding attractions. Lake Mead National Recreation Area, as originally established, included all the lands surrounding Lake Mead and extending downstream from Hoover Dam on both sides of the Colorado River for almnst 40 miles. In 1947, the area was enlarged to encompass Lake Mohave and a shorr stretch of the river below Davis Dam, 67 miles below Hoover. Visitors to the Lake Mead National Recreation Area numbered about 6 million in 1983. These visitors came from all parrs of the United States and from many foreign lands.