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3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish peak discharge-frequency relationships for each flooding source studied by detailed methods affecting the community. Peak discharges for the 1-percent annual chance flood for studies withiri the City of Cortez were developed using PondPack 9.0 software by Haested }Vlethods. SCS Curve Numbers and the SCS Unit Hydrograph were utilized for the rainfall- runoff simulations. Additional information is provided in the H drolo ~ic Studv, City of Cortez, Colorado (Goff Engineering, October 2005). Peak discharges for the 10-, 2-, 1- and 0.2-percent annual chance floods for the Dolores River and West Dolores River were determined by utilizing a flow frequency analysis of flows at the "Below Rico" (1914-1915, 1919-1921, and 1952-present) and "At Dolores" (1896-1903, 1911-1912, and 1922-present) stream gaging sta.tions on the Dolores River, Gage Numbers 09165000 and 09166500, respectively, and following guidelines established by the U~S. Water Resources Council. To determine the type of event that would cause the larger, less frequent floods, snowmelt floods and rain floods at the Dolores Gage were separated and statistically analyzed. At the Rico Gage this type of analysis was never determined because of the short period of record. Based on the flows on the 1970 flood at the Dolores and Rico Gages, Curve and optimization techniques were used to develop unit hydrogra Dolores R.iver. Optimization of the unit hydrograph for Lost Canyon achieved by using data from the October 13, 1941, storm and flood. consistent with studies performed by the COE, Los Angeles District, a~ Bureau of Reclamation, calculated by the COE, Sacramento, were fi reasonable and accurate. Peak discharges for the 1-percent annual chance flood for the Dolores West Dolores River were updated in 2005 using hydrologic software by the Army Corps of Engineers Hydrologic Engineering Center (H Geospatial Hydrologic Modeling Extension (Geo-HMS) was used watershed data and subdivide the basin; the Hydrologic Modeling Syst computer program was used for analysis of the precipitation-runoff p~ the study azea. Results of this evaluation were compazed to the 100 discharges developed from the Rico and Dolores gages and were four agreement, which validated the rainfall runoff model. Additional infc provided in the Hvdrolo~Report for the Dolores River near polores Flood Insurance Studv (U.S. Army Corps of Engineers, Sacrament August 2005). Peak discharges for the 10-, 2-, 1- and 0.2-percent annual chance flooc Mancos River were based on a flow-frequency analysis prepared by the nyder S- s for the •eek was ~ss rates, the U.S. zd to be ver and :). T'he process i (HMS) ;esses in ~ar peak to be in iation is District, for the ~E. In 10