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<br />therefore providing some residual flood control effects. <br /> <br />In the plains <br /> <br />area downstream of Lyons, numerous sma"I_J storage faei Ii t:jefi exist <br /> <br />constructed mai.nly for agricultural purpo:~':ef::. <br /> <br />Though these reRervolrs do <br /> <br />have some residual flood control effeetsJ, their benefits are f~ssf!ntia11y <br /> <br />negligi.ble compared to Buttonrock Reservoi r" <br /> <br />The topographic features downstream of Lyons, Colorn,Qo are mai.n]y <br /> <br />dominated by farmland, open pasture land, i nd ,I in several areas, open pit <br /> <br />gravel mining. Due to the gravel mining :~'perations that are currently <br /> <br />under operations and those that have occlJrred in the past, a numher of <br /> <br />large depressions exist scattered along I::lh~ overbanks of the St. Vrain <br /> <br />Creek. <br /> <br />In view of the fact that availal: le depression storage during a <br /> <br />major event would be unknown, it was assumed that these depressior:. areas <br /> <br />were full and thus would not attenuate peak ~lQws. <br /> <br />Study Reach Description <br /> <br />The limits of the study run from the Bou :i_d 2r-\.>leld County Line s known as <br /> <br />East County Line Road, upstream approximat("'v 1.0 mile to 119l:h Street. <br /> <br />The study reach lies along the City Df Longmont's south corporate <br /> <br />boundary. <br /> <br />The channel is well defined with an aver a;;" streambed slope through the <br /> <br />study reach of approximately nine feet p"" mile (slope 0' 0.2 percent). <br /> <br />Distances from defined left and right overllim:<s range from 50 to 100 fef~t. <br /> <br />The overbanks are made up mostly of fannlnnc:~ and open pastures. The .left <br /> <br />overbank, looking downstream, for the mU::li: part rises abruptly in <br /> <br />elevation, while the right overbank terrain :i s typ;.cally uniform in grade ,. <br /> <br />9 <br />