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Insurance Study. Maps and flood elevations will be amended periodically to reflect future changes. 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 floods of the 10-, 50-, 100-, and 500-year recurrence intervals were determined by utilizing a flow- frequency analysis of flows at the "Below Rico" (1914-15, 1919- 21, and 1952-present) and "At Dolores" (1896-1903, 1911-1912, and 1922-present) stream gaging stations 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 of the 1970 flood at the Dolores and Rico Gages, Snyder g-Curve and optimization techniques were used to develop unit hydrographs for the Dolores River. Optimization of the unit hydrograph for Lost Canyon Creek was achieved by using data from the October 13, 1941, storm and flood. Loss rates, consistent with studies performed by the COE, Los Angeles District, and the U.S. Bureau of Reclamation, calculated by the COE, Sacramento District (Reference 1), were found to be reasonable and accurate. Peak discharges for floods of the 10-, 50-, 100-, and 500-year recurrence intervals for the Mancos River were based on a flow- frequency analysis prepared by the COE (Reference 3). In the analysis, the flood peak estimates were determined from a regional analysis of peak flow data from stream gaging stations in the area. Peak discharges for floods of the 10-, 50-, 100-, and 500-year recurrence intervals for Chicken Creek were computed using regionalized basin parameters determined by the COE for the Mancos River. Comparative hydrologic calculations were also determined for the Chicken Creek Basin using the Manual for Estimating Flood Characteristics of Natural-Flow Streams In Colorado (Reference 4), as well as unit area discharges. Peak discharge-drainage River, Dolores River, Chicken Creek are shown area relationships for the West Dolores Lost Canyon Creek, Mancos River, and in Table 1. 6