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SECTION V CRITERIA INTRODUCTION Most of the Impacts of urban development have an effect on the sto"m runoff system. It Is Important to recognize, whl1e attempting to Integrate the multitude of requIrements for the urban system,. that the major draInage system wIll operate whethElr or not It Is planned or designed, and whether or not urban development Is wIsely 10c!lted ,,11th respect to It. Thus, major draInage needs to be gIven high, early prIorIty when considering the urban systllm so that storm runoff Is handled as an asset and not a liability. It Is Important that the desIgn crIteria be well-conceIved sO as to maximIze the benefits to be obtained from each alternate and to Insure that the major drain- age system wIll operate as Intended. The design criterIa utilized for thIs storm drainage pIlot planning study are those contained In the Denve,r RegIonal Council of Governments' Urban Storm D ra I nage G-rl ted 1Il Manua I, Vo'l ume Nos. I and 2. These crIteria are summarIzed below. Also presented are recently developed supplemental crIterIa for non-structural approaches such as flood plaIn zoning. STRUCTURAL CRITERIA Specific planning and design crIteria applicable to Lena Gulch are: 1. Grass-LIned Artlflcal Channels. Des Ign will generally be based on channels having natural waterway hydraulic and appeanmce characteristIcs. They should be aesthetically de,slgned to the local envIronment and useful for 10c:.91 recreatIon continuous along the channel. Criteria Include: a. A maximum average design velOdty of eight fps for th,~ 1 DO-year storm. b. Design depth on over-bank of up to four fee,t, except I.here top wldth-to-depth ration e~ceeds thl rty, ,,,nd then not more than fIve feet (except for short durations where velocity considerations are made). c. Side slopes generally of 4:1; acceptable from 3:1 to ';:1 or more. d. Centerll ne curvature of twice th,e top ",i dth, but not I ess than 100 feet.