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. . . characterized by moderate peak flows and large volumes of water over a long duration. The peak flows have a noticeable diurnal fluctuation. Snowmelt flooding may occasionally be augmented by rainfall. Research of the study area yielded minimal information regarding flooding events in Rockvale. In spite of the long history of human activity, there are limited historical accounts of major flooding on Oak Creek and South Oak Creek in the Rockvale area. On June 5, 1921 a cloudburst rainfall fell on the foothills in the Rockvale/Coal Creek/Williamsburg area. Peak discharges for Oak Creek and Coal Creek at Florence were estimated by the USGS to be 2,760 and 3,720 cfs, respectively. Damages were estimated to be a quarter of a million dollars and 16 lives were lost in the Town of Florence. No specific information is available for damages in Rockvale for that event. Other noteworthy rainstorms in the area occurred in 1909, 1932, 1941, 1948, 1949, and 1965. More recently, damage as a result of flooding on Oak Creek occurred during the spring of 1995 in the Town of Rockvale. Rapid melting of snowpack in the upper watershed caused higher than normal peak flows through Rockvale which washed out a portion of South Oak Creek Road, and nearly caused damage to a water main buried under the roadway. The high water on Oak Creek was reported to be just below the low chord of the Mesa A venue bridge, No lives were lost during that event, but damages are estimated to be on the order of $100,000, Community Resoonse to the CWCR Desi211ation and Aooroval Process A letter from the CWCB was transmitted to the Town of Rockvalee regarding the Board's proposed action for designation and approval of this Floodplain Information Report and the Rockvale FIRM. The Town was very receptive to the Board's proposed actions. The Town sent an official letter requesting that the CWCB designate and approve floodplain information currently available to the community, A copy of the request letter is included in the Appendix at the end of this report. ENGINEERING METHODS Hydrololrlc Analysis Hydrology information for Oak Creek and South Oak Creek on Rockvale's FIRM has been estimated in accordance with the CWCB's Guidelines for Determining ZOO-Year Flood Flows for Approximate Floodplains (Guidelines), The lOO-year flow for Oak Creek and South Oak Creek can be estimated by utilizing the regression equation for Arkansas River Basin, Subregion Ark-3. The equation is QUNI = l089,27(A)o.635 , where QtoO is the l00-year peak flow in cubic feet per second, and A is the upstream (contributing) drainage area in square miles. The regression equation is only valid for tributary streams having drainage areas between 1 square mile and 930 square miles. Figure I, presented in the Appendix of this report, displays the Arkansas River Basin with Subregions Ark-I through Ark-6. The regression curve for Subregion Ark-3 is also included in the Appendix. A detailed study or other hydrologic analysis must be performed for projects involving streams with drainage areas that fall outside the applicable range. Table I displays the estimated loo-year peak flows for Oak Creek and South Oak Creek at the downstream Town limits.