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HYDROLOGY (EFFECTS OF NEW D.A-~PA) GENERAL In reviewing available information, our firm decided to pursue an approach to this analysis similar to that used by the Corps for their 1981 study, Reasons for this course of action are cited below: o A preliminary log-pearson Type III discharge probability analysis performed by our firm using all of the available gaging data (Appendix 5) indicated small rela1:ive differences between the lOO-year discharge which we calculated and the 100-year discha.rge which the Corps reported in 1973. o In discussing the results of our preliminary analysis with personnel from the Corps Hydrologic Engineering Branch in Omaha, who conducted the 1973 and the 1981 study, it was suggested that this might be a reasonable approach, depending of course on review of the final results. In establishing discharge probability relationships to the gaging records, the guidelines set forth in WRC Bulletin #17B, which supersedes the earlier WRC Bulletin #17, were followed. In order to prove consistency with the previous Corps studies, an attempt was made to duplicate key Corps results from their 1973 and 1981 studies before continuing our analysis with more data (Appendix 1). PROCEDURE Gaging records for both the gage at the bluffline and the gage near Greeley were analyzed. For purposes of comparison, the procedure outlined below was performed on the data set available to the Corps at the time of the 1973 study, again for the data set available for the 1981 study, and then for the entire data set available at the time of this writing (through 1984), The data used was retrieved from the WATSTORE data base maintained by the Corps, and is submitted in Appendix 5, The procedure set forth in WRC Bulletin #17B is shown in schematic form in Appendix 7. The qeneral methodology used in our analysis was as follows: Page 6