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<br />11 <br />11, <br />II <br />II <br />il <br />II <br />II <br />'I <br />I <br />'I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />11 <br />11 <br /> <br />Lower Big Dry Creek Hydrologic Study <br /> <br />Preservation offloodplains is a policy of the District to manage flood hazards, <br />preserve habitat and open space, create a more livable urban environment, and <br />protect the public health, safety, and welfare (White 1945). <br /> <br />12. Reserve Suffident Right-of- Way for Lateral Movement of Incised Floodplains. <br />Whenever a floodplain is contained within a narrow (i.e., degraded) channel, its <br />lateral movement over time can cause extensive damages to public and private <br />structures and facilities. For this reason, whenever such a condition exists, it is <br />recommended that, at a minimum, the channel be provided with grade control <br />structures and a right-ofway corridor be preserved of a width equivalent to the <br />cross section recommended for a grass-lined channel, including a maintenance <br />access roadway. <br /> <br />The communities in the urbanized portion of the Big Dry Creek Watershed subscribe to these <br />policies, have reiterated them in their own manuals and participate in regional drainage planning <br />based on these principiles. For the most part, the design criteria developed for the urbanized area <br />are consistent with UDFCD's policies, which are, in turn, consistent with national standards. <br />One of the key requirements is to detain stormwater to control peak runoff rates to approximate <br />pre-development levels for specific design storms and to detain stormwater to improve water <br />quality. This practice :results in controls on peak discharge rates for commonly occurring smaller <br />storms to less frequently occurring larger storms. Tables 4 and 5 summarize the detention <br />requirements and release rates, respectively, for the communities in the watershed upstream of <br />Weld County. <br /> <br />Table 4. <br />Detention Requirements for Developments <br /> <br />City/County \" ater Quality 2-year 5-year 100-year <br /> Capture Volume <br /> (WQCv) <br />Westminster X X X <br />Broomfield X X (residential) X (commercial/public) X <br />Thornton X X X <br />Adams County X X X <br /> <br />971-179.092 <br />June 2005 <br /> <br />Wright Water Engineers, Inc. <br /> <br />Page 28 <br />