Laserfiche WebLink
<br /> <br />2 <br /> <br /> <br />Determination of the PMF for Hoover requires that the design storm <br />be located either in the basin between Hoover and Glen Canyon Dam or <br />in the basin above Glen Canyon Dam. Hoover and Glen Canyon Dams, as <br />well as other upstream dams, are operated as a part of the Colorado <br />River system of reservoirs. The PMFs were developed for both dams <br />in this study. <br /> <br />Personnel of the Flood Section of Reclamation's Denver Office <br />concluded that the design scenario required to produce a reasonable <br />probable maximum flood inflow to these dams would include four <br />specific conditions. These are: (1) the accumulation of an optimum <br />snowpack over the Colorado River Basin during the preceding winter <br />and spring, with low temperatures and continued snowpack <br />accumulation into the late spring; (2) high levels of ground wetness <br />and river flow occasioned by a preceding high runoff year; (3) rapid <br />snowmelt resulting from relatively high temperatures following the <br />snowpack accumulation season; and (4) the occurrence of a design <br />storm (which may be comprised of a series of storm events) during <br />the recession limb of the snowmelt runoff hydrograph. <br /> <br />1.2 STUDY SCOPE AND PARTICIPANTS <br /> <br />The preliminary work on the PMF study began in January 1986. In a <br />normal situation the development of design storm data would be <br />conducted by the Flood Section at the Denver Office of the Bureau of <br />Reclamation. The Flood Section, however, was not able to complete <br />the necessary meteorology to determine the probable maximum <br />precipitation (PMP) for the study area within scheduled time frames <br />because of commitments to other on-going studies. Therefore, <br />meeting those time frames required the services of an <br />Architect/Engineer firm staffed with professional engineering <br />personnel that had knowledge of development of such design data. <br />Steps were taken to identify and acquire the services of a <br />consulting firm with the necessary expertise. Using the Lower <br />Colorado Region'S indefinite quantity contract with Morrison-Knudsen <br />Engineers (MKE), the services of qualified hydrometeorologists were <br />obtained. <br /> <br />A task order was issued in April 1986, to MKE to develop a Plan of <br />Study (PaS) to acquire the necessary hydrometeorological design data <br />for Hoover Dam. The pas was completed on July 1, 1986, for $34,700. <br />The pas identified five study parts estimated to cost about $990,000 <br />and would require nearly 3 years to complete. The five parts were: <br /> <br />1. Initial Project Specifications. <br />2. Phase I - Optimum Snowpack Accumulation and Critical Melt <br />Criteria. <br />3. Phase II - Development of Upper Limit Design Rain Storm(s) <br />(ULDRS) . <br />4. Phase III - Need for and Determination of Storms Less Than <br />ULDRS (for use in combination with Phase I). <br />5. Phase IV - Evaluation of Less Than Optimum Snowpack for <br />Use in Combination with ULDRS. <br /> <br />The five study parts were examined in detail, and the implications <br />of doing or not doing some of the phases or portions thereof were <br />