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<br />Task 1 <br />During the last several years, various efforts have been completed which provide <br />technical reports and information related to PMP estimates for the Cherry Creek drainage basin. <br />These efforts will be reviewed to provide a summary of the technical approaches used, <br />assumptions made and discussions on consistency with previous studies and physical principles. <br />The following documents will be technically reviewed: <br />National Weather Service's Site-Specific Study (NWSSS), 7/13/1995 <br />NWS's Response to Comments, 7/10/1997 <br />NWS's Response to Comments, 0/05/1999 <br />Public Presentation Material, 7/21/1999 Meeting <br />Technical adjustments to the design standards as presented in HMR 52 and 55A <br />NWS's definition ofPMP <br />A summary of the conclusions of these technical reviews will be provided and will <br />provide background for the proposed PMP study. Additionally, the National Weather Service=s <br />Antecedent Moisture Study, 7/15/1997 will be technically reviewed and comments provided on <br />the analysis approach used and the reliability of the conclusions. <br /> <br />Task 2 <br />A W A will request copies of all working papers and files from NWS related to their 1995 <br />site-specific PMP study. A project team member will visit the NWS office of hydrometeorology <br />in Silver Spring Maryland to discuss the details of the study and to collect the working papers <br />and data files available. A W A will replicate the calculations performed by NWS using the HMR <br />52 software and the GRASS GIS system (see Task 9). Results from these calculations will be <br />compared with GRASS GIS files provided by NWS and any differences documented. If errors <br />in the NWS calculations are found, they will be corrected and the PMP values recalculated. The <br />results will be summarized in an interim report and presented to the technical review panel. <br /> <br />Task 3 <br />There are many variables which influence the computation of PMP values. Some of <br />these variables have a very significant influence on the PMP values while others are less <br />significant in determining the PMP rainfall depths. A sensitivity analysis will be performed on <br />the following variables as defined in the NWSSS: <br />1: Dewpoint temperatures. Precipitable water ratios will be evaluated to quantify the <br />effect of changes in either the storm representative dewpoint or the maximum dewpoint. <br />2: Duration of the PMP storm event. <br />3: Storm positioning over the basin. Changes in positioning the storm center on the <br />volume of rainfall which falls within the basin boundary will be calculated. <br />4: Incremental Time Distribution for the Design Storm. <br />5: One percent chance rainfall correlation. This sensitivity is dependent on how the <br />100-year point rainfall values are used in site-specific PMP computations. <br />6: Orographic effects as Determined from Scientific and Historical Logic. This effort <br />will depend on items 3: and 4: above. <br />