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<br />Drop Structures in the Real World <br />Guidelines for Drop Structures in Grass Lined and Wetlands Channels <br /> <br />William C. Taggart', William G. DeGroof,.I<atherine J. Chase3, Peter L. Nelson4 <br />o>p,.,.I'v- S"fo.tlOr- <br /> <br />INTRODUCTION <br /> <br />The Urban Drainage and Flood Control District (UDFCD) began in 1969 as an <br />intergovernmental agency to coordinate the drainageways in the Denver Boulder <br />Metropolitan areas. With time the UDFCD's property tax and responsibilities <br />increased to include design, construction, and maintenance assistance to the <br />communities. The UDFCD has also expanded its original Urban Storm Drainage <br />Criteria Manual (USDCM by UDFCD, 1990, 1992) to include hydraulics and <br />hydrology updates, wetlands waterways, stormwater quality, and erosion control. <br /> <br />Communities work with the UDFCD to obtain partial funding assistance on <br />construction of public projects, and submit some or all development proposals to <br />be eligible for maintenance assistance. UDFCD and its guidelines have a strong <br />influence on the facilities constructed. However, some communities allow lesser <br />standards on certain projects and in certain circumstances. A wide variety of drop <br />structures, channel and multi-purpose projects have been constructed and can be <br />observed in a real world laboratory. <br /> <br />GRASS LINED AND WETLANDS W A TERW A Y CRITERIA <br /> <br />UDFCD has been heavily oriented towards floodplain preservation and grass lined <br />channels, for which drop structures play an important role in an urban <br />environment. The key grass lined channel design criteria is oriented towards 100 <br />year discharge maximum velocities of 1.4 to 2.1 rnIs (4.5 to 7 fps) for erosion <br />resistant soils, and 0.8 to 1.5 rnIs (2.5 to 5 fps) for easily eroded soils. Numerous <br />other design considerations are expressed. A maximum depth of 1.5 meters (5 <br />feet) outside the trickle channel is called for. <br /> <br />Design criteria are also presented for wetlands waterways. The designer must use <br />the 2.1 and 1.5 rnIs (7.0 and 5.0 fps) velocity criteria for a new channel, but also <br />consider depths as a result of the mature wetland growth and numerous other <br />factors. <br /> <br />'President, 3Associate, 4Associate, Taggart Engineering Associates, Inc. (TEA), <br />2525 16th Street Suite 210, Denver, CO 80211 <br /> <br />2Chief, Floodplain Management Program, Urban Drainage and Flood Control <br />District, 2480 West 26th Avenue, Suite 156B, Denver, CO 80211 <br /> <br />1 <br /> <br />Taggart, et al <br />