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iJJ11J Ckf1? wIll. ;~,.n .... Additional Tasks for the Cherry Creek Site-Specific PMP Study Denver, Colorado <. SCOPE OF WORK August 2003 Project Location and Objectives - The project location is in Arapahoe and Douglas counties for the Cherry Creek Reservoir, which is in the Denver Metropolitan Area. The objectives of this project are to evaluate the Corps's 1995 PMP study for the Cherry Creek Reservoir and develop regional PMP study parameters and basin characteristics that are reasonable the Denver, Colorado Region. The Board is performing these tasks in response to a 1999 General Assembly Resolution. The project tasks shall be accomplished with considerations for all pervious works that A W A has previously performed for the subject project. The additional tasks that are to completed for the subject project are: Task 1 - Additional Extreme Storms Evaluations The NWS reviewed storm events both outside of Colorado and over the Colorado Front Range foothills that they considered should have been evaluated for use in the Cherry Creek PMP study. Additional analyses of these storms are required to evaluate their applicability for the Cherry Creek stUdy. If it is determined that any of these storms should be included, adjustment factors need to be determined for those storms. These include Gibson Dam, MT, 1964; Spring Brook, MT, 1921; and Big Elk Meadows, CO, 1969. Task 2- Develop Envelopment Curves To provide spatial continuity among various area sizes both larger and smaller that the Cherry Creek drainage basin, depth-area (D-A) analyses should be included in the Cherry Creek PMP study. D-A curves from all storms considered in the study need to be developed and an enveloping curve constructed. The amount of envelop1llent resulting from the D-A analysis for the area size of the Cherry Creek basin will be applied to the PMP values for all durations. Task 3 - Prepare Depth-Duration Curves In order to apply the site-specific PMP values in PMF modeling, a temporal sequence needs to be developed. This includes depth-duration (D-D) analyses of all storms and development of a temporal sequence of hourly PMP values based on envelopment results from the D-D analyses. Task 4 - Prepare a Third Draft Final Report Prepare and present the third Draft Final Report and provide copies to the Cherry Creek Advisory Committee for review and comments. Publish a Final Report for the Cherry Creek Site-Specific PMP Study with additional addendurns as required. ~. t\~' ,~ 'e" ''',';'-,-'-' ,~J~:~;.~J~;if"__t',,~ iF..''''~... ~:t~\ ~~";jh~1'