OCR Text |
Show v Photo on ihe left is an artist's conception of Rainbow Bridge as it is now while the picture Powell's tremendous capacity of 27 million acre-feet was rteflgned to store exces? flows ever a number of wet years. When the inevitable dry cycles occur, Lake Powell's water will then be used to meet downstream commitments. commit-ments. Lake Powell will thus guarantee water for future projects in upstream areas. Water from Lake Powell is dropped through Glen Canyon Powerplant to turn out kilowatts kilo-watts to energise industry and to light Western cities. Revenue from the sale of the power repays the cost of Glen Canyon Dam and Lake Powell. The amount of power that can be produced depends on the "head," the difference between the elevation of the surface of the lake and that of the river below the dam. Although the law authorizing authoriz-ing Glen Canyon Dam included in-cluded provisions to keep Lake Powell out of Rainbow Bridge National Monument, Congress repeatedly refused to appropriate funds to construct con-struct the necessary barrier dam, the report states. At the same time, Congress did appropriate funds for construction con-struction of a full-sized Glen Canyon Dam that could hold Lake Powell at elevation 3,700 feet. No Effect The report contends that P, 3 jnbnw Bridge is carved on the right shows Lake Powell at elevation 3680 feet with a drawdown line of 20 feet. Agency Defends Higher Level for Leake Powell Published recently by the Upper Colorado River Commission Com-mission is a booklet concerning concern-ing the relationship of Lake Powell to Rainbow Bridge and it lists some of the reasons for raising the level, of the lake to 3.700 feet. Lake Powell, the booklet states, plays a key role in the Colorado River Storage Project; Pro-ject; without it many planned plan-ned uses of Upper Basin water wa-ter could not take place. According Ac-cording to the original plan authorized by Congress. Lake Is - ' J v- - - : - ' UVV ; ipELEV.3732 St-' -V k" :.,.;, " v VELrv.3721 'f " - f LAKL fOvrl, Pt:SEM.0!3 kaycnTA ! ST WATER SURFACE EL6V.370Q.. . I ' SANDSTONE 'ULL RESERVOIR). . ? ; . . ... .l-. -T- LgVi3S54 - j This schematic drawing shows the level of Lake Powell at 3700 fM pacify, below Rainbow Bridge. The lake level from Navajo sandstone and rests on a platform of !tic much harder and denser Kay-enta Kay-enta sandstone. Bridge Creek has cut a gully 67 feet deep into the Kayenta directly beneath be-neath the bridge. An examination examin-ation made by the U. S. Gn- , ological Survey concluded, the report says, that the Kayenta sandstone was fully competent compe-tent to support an arm of Lake Powell without damage to Rainbow Bridge. Since the Kayenta is already saturated, the report continues, with ground water (as indicated by many springs), standing water of Lake Powell could not in any way impair the stability of the bridge. Only Half of Capacity Listed as adverse effects of limiting the elevation of Lake Powell's water to 3,600 feet are that the capacity of the lake could be cut in half because be-cause the canyon widens between be-tween elevations 3,600 and 3,700 feet and the top 100 feet of the lake contains half of the capacity. Power production pro-duction would be cut due to the loss in "head." Glen Canyon Can-yon Dam would have to be operated without a spillway because the spillway is located locat-ed at elevation 3,648 feet and could never be used. Each winter the lake would have to be lowered to provide for runoff during the spring. Fin- p'h'. phrmt20 per cent of the potential water-use projects in the Upper Basin would have to be shelved because the lake would not have enough en-ough storage capacity to make the legally required downstream deliveries of water wa-ter during drouth cycles. Listed as alternatives are the possibilities of building a barrier dam which the report contends would be outrageously outrageous-ly expensive and construction of such a dam would deface, the wilderness landscape with extensive and ugly scars. The report concludes by saylrg that by allowing the lake to rise to its full level, it wojU cause no appreciable harm to Rainbow Bridge, yet it would permit wise use of water and power sources centering about Lake Powell. The white drawdown mark that would occasional'y be seen when the lake was low ered would seem to be minor damage when compared to the serious consequences of other alternatives, the report says. will lie in the Kayenta sandstone some 21 feet, below the base of the bridge which is formed of Navajo sandstone. |