WSP03375 - Laserfiche WebLink

Home Browse Search

.. from August I to January 1, is the vacant space-building period preparatory to the snow melt season. During this period, the flood control regulations stipulate a minimum vacant reservoir storage space at all times starting with 1.5 maf on August 1, and the building of additional system storage space each month, increasing linearly through January, to achieve a minimum vacant reservoir storage space of 5.35 maf by January 1. The uppermost 1.5 maf of storage in Lake Mead is allocated exclusively to control rain floods. The second operational season, from January 1 to July 31, is essentially a snow melt wflood routingW period, ending again with the minimum 1.5 maf of vacant reservoir storage space required on August 1. During this period, release decisions are directed by a prescribed computation. The computation considers the current forecasted unregulated inflow volume through July which will not be exceeded 19 out of 20 times (the probable maximum forecast), current vacant storage space in Lakes powell and Mead, effective flood control space in upstream reservoirs, miscellaneous losses, and the time available to pass the probable maximum forecasted inflow. For any given month and forecasted inflow volume, the computations determine a mandatory minimum flood control release level for the current month. The flood control regulations provide for stepped minimum releases from Hoover Dam of 0 cubic feet per second (cfs), 19,000 cfs, 28,000 cfs, 35,000 cfs, 40,000 cfs, and 73,000 cfs, respectively. The lowest step, 0 cfs, corresponds to times when the regulations do not require flood control releases. The last step, 73,000 cfs, is the maximum controlled release from Hoover Dam without a spillway flow. The maximum Hoover Dam flood control release objective since the completion of the dam has been 40,000 cfs. Encroachment of permanent and semi-permanent development into portions of the flood plain resulted in substantial property damage with a 40,000 cfs release from Hoover Dam in 1983. The Colorado River Floodway Protection Act of 1986 (P.L. 99- 450), provides for establishing a federally declared floodway below Davis Dam. The floodway is to be capable of accommodating either a one-in-one hundred year river flow consisting of controlled releases and tributary inflow, ora flow of 40,000 cfs, whichever is greater. It will serve to preserve the water conservation capability of the river's reservoir system, minimize damage to property and natural resources, protect public health and safety, and reduce the threat of loss of human life under full reservoir conditions. Alternatives for greater flood protection through smaller flood control releases would increase the amount of storage space that would be needed for flood control, thus requiring -10-