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<br />V-6 <br /> <br />As envisioned, the area would have a series of dry detention ponds <br />which would fill during a major flood. The diversion structures will <br />fill partially on an average of once every two years. Otherwise, <br />they will remain dry most of the time. Each of these pools would <br />have a diversion structure from South Boulder Creek. Each would <br />have a spillway leading back to the Creek so the embankment would <br />be threatened by overtopping only during floods of much greater than <br />the 100-year return interval. Each of these ponds would have an <br />outlet designed to drain it over a period of several days following <br />the flood, so they could again be used as parks and have storage <br />capacity for any subsequent floods. <br /> <br />These structures could be located along the west side of South <br />Boulder Creek throughout its length between Marshall Road and <br />the Denver-Boulder Turnpike. Also, such a structure could be <br />located between the turnpike and South Boulder Road. If a ten <br />foot embankment and excavation of the pool area to a depth of about <br />two feet is used at these areas, a detention storage of about I, 100 <br />acre-feet is possible and the flood could be reduced to approxi- <br />mately 2,000 cfs. If only a five foot embankment is used in this <br />area, the flood can be reduced to approximately 3,000 cfs. The <br />ten-foot embankment alternative would cost about $870, 000 including <br />land acquisition and provide estimated benefits of approximately $380,000. <br /> <br />Levees. Levees or berms are embankmen~s designed to prevent <br />flood waters from inundating specific areas. They can provide <br />a me,ans of effective and inexpens ive flood protection. They are <br />especially effective in controlling shallow flooding in wide areas. <br /> <br />The area along the north and south side of the Denver-Boulder <br />Turnpike would have widespread shallow flooding in the event <br />of major flows in the creek. The possible flooding would be due <br />in part by the construction of the turnpike. Flood waters could <br />spread northwest around the South Boulder Road interchange, <br />over the turnpike and into parts of the Keewayden Meadows area. <br />At this point the flows would be west of 47th Street bypass which <br />could present possible additional drainage problems. <br /> <br />A levee with low side slopes could be constructed west of South <br />Boulder Creek, both north and south of the turnpike. The prelimin- <br />ary estimate of this alternative is $16,000. The benefits are diffi- <br />cult to quantify since detailed mapping for a portion of the flooded <br />areas is unavailable, but are estimated to be in excess of the <br />estimated construction costs. <br /> <br />