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serving the Southwest United States 0 The Glen Canyon facilities are used for peaking purposes in the system, resulting in hour by hour, weekend and seasonal variations in the otherwise uniform annual release. Lake Powell is still in the process of initial filling and there are interim operating procedures for coordination with power production at Hoover Power Plant; coordinated operations also consider water surface fluctuations at Lake Mead in connec- tion with the spawning habits of the bass fishery 0 Within these overriding requirements, it has not been pOSSible to give special consideration to river travelers who, nevertheles s, receive many incidental benefits 0 As a service, the Bureau of Reclamation furnishes prospective hourly flow charts to assist experienced river guides in scheduling progress through the canyon, taking advantage of the daily peak releases or the low flows as the situation war- rants 0 'I c, " Figure 1 indicates the hourly amounts of discharge anticipated at four of the major rapids in Grand Canyon 0 Similar charts for other rapids are also available 0 ',' \ :~ ~:.: Figure 2, a Flow-Time Relation Chart involving two typical discharges through Grand Canyon, illustrates how the daily fluctuations are gradually absorbed as the flow proceeds downstream. ',' Figure 3 illustrates how river regulation at Glen Canyon Dam is extending the river boating season through supplementing low period flows. The shaded areas indicate a band between daily peak flows and daily mini- mum flows anticipated at Lees Ferry in the year 1971. For reference purposes, typical years of high (1957), moderate (1948), and low (1954) runoff have been superimposed on respective illustrations (a), (b), and (c) 0 " ,', r:. Under the new river regimen, the profile of the main channel remains in its staircase form with relatively calm waters above and below extensive rapids formed by boulders and debris deposits at the confluence of the side channels. The main river still jostles and rearranges these deposits, but, being limited to about 20,000 cubic feet per second, is not as powerful in this respect as formerly when the discharge at times rose to over 100,000 c of. so . t; ~;-. ", " ~,' .. '.~ p" '" ~ ..." ,,' <' " RIVER TRAVEL The availability of war surplus rubberized pontoons, strapped together to form large flexible rafts capable of supporting as many as 20 passengers and their gear, accounts for some of the recent popularity of river travel through Grand Canyon 0 Avoiding the low flow and the extreme high flow seasons, river runners formerly used wooden or fiber crafts carrying one or two passengers 0 There is now only an occasional use of these small rigid 3