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This project was a technical review of the Corps of Engineers and National Weather Service, July 13, 1995, a Probable Maximum Precipitation (PMP) Study for the Corps Dam Safety Investigation of the Cherry Creek - Dam and Reservoir. This project also developed into a site- specific analysis for a PMP event in the Cherry Creek Basin. The Board, in cooperation with the Cherry Creek Work Group, performed a technical review of the Corps of Engineers' PMP investigation. The Board along withlocal governments in Douglas and Arapahoe Counties selected Applied Weather Associates to perform the PMP review and a new site-specific PMP analysis. A team of close to ten noted professionals comprised the A W A team. The project received much interest using regional procedures for the determination of PMP values for the Cherry Creek Basin in Colorado rather than general national procedures. The PMP values are the key, basic elements for the Corps Dam Safety Study. The non-federal PMP study findings will be significant information in the general public acceptance of any proposed reservoir operations or dam modifications. The Final report is being prepared and the analysis was not changed based on the National Weather Service participation at the final meeting. It was determined through discussion by many experts at the final meeting that the A W A study findings were based on acceptable PMP procedures, regional storm events of PMP magnitude, and maximization methods that appropriately represent the Cherry Creek basin. Lou Schreiner of the BOR is considered by many to be the top expert in Dam Safety and PMP issues. He is also considered to be the most thorough and competent reviewer of studies in the PMP arena. The three technical panel review members, Lou Shcreiner - BOR, Nolan Doesken - Colorado Climate Center, and Gary Lewis -- Parsons Engineering endorsed the study results and conceded that their concerns were addressed and incorporated into the final study findings. The 24-hourbasin wide comparison would be 15.4inches for the AWA study and 21.7 inches for the NWS study, a difference of 27% lower. This number is in line with previous site-specific studies versus regional analysis studies. This difference in maximum rainfall can make a large difference in the volume of rainfall in a flood, flood damages and the ultimate recommendation for dam safety improvements at Cherry Creek Reservoir. Outcomes from the final meeting discussions were that the NWS use ofHMR 52 in a HMR 55A region was a inappropriate and that an applications manual for the HMR 55A region should be developed similar to HMR 52. _ The CWCB and A W A have completed the project and have exceeded the performance objectives of the original scope of work completing a very detailed analysis of the Cherry Creek Basin. The CWCB staff will seek endorsement of the CWCB Board and the project sponsors will seek endorsement by county commissioners and city councils. Potential outcomes for this project are (I) to take both studies to the National Science Foundation to figure out which study is more correct or (2) possibly using both of the studies numbers in a probable maximum flood study and to compare the flood volumes and .flood damages and then make some decisions based on the risk involved. One of the most telling National Weather Service comments from the final meeting was there have been half a dozen PMP events in all of the United States documented to date. One of the most telling comments from the final meeting from the technical review panel members was that we and our children are not very likely to see a PMP event in Colorado. 9. Boslev Wash Feasibility Studv and Demonstration Proiect Authorization: HB 00-1419 Grant Amount: $75,000 Water Source: N/A Project Type: Flood Control Location: Mesa County - near Clifton Project Manager: Larry Lang Sponsor: Mesa County Beneficiary: Mesa County This project is a Drainage Way Master Planning, Preliminary Drainage Design, Floodplain Delineation Study on Bosley Wash and Stub Ditch in the Grand Valley. The stream experienced three major flood events in the summer 1999. HDR Engineering was selected to perform the engineering work for this project, and a contract has been signed with Mesa County. Work on the project is underway. The study evaluated the flood risks throughout the basins and floodplains, determined the hydrologic and hydraulic characteristics of the study reaches, delineated the flood hazard areas, and formulated flQod mitigation measures. A draft report has been prepared that presents the study findings and recommendations. The report is under review by the project sponsors and looking to be adopted by the local officials. The study produced project recommendations for a couple of different options for a demonstration project. FloQdplain study was completed for $50,000 and there e