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<br />. <br /> <br />Kelly Road Dam was originally designed to store runoff for <br /> <br /> <br />floods somewhat greater than the lOa-year event. At that time, <br /> <br /> <br />the Highline Canal diverted runoff from the sparsely developed, <br /> <br /> <br />highly pervious area upstream from the canal and this area did <br /> <br /> <br />not contribute to the inflow to Kelly Road Dam. <br /> <br />Extensive development in the basin since Kelly Road Dam was <br /> <br /> <br />constructed has caused substantial increases in potential runoff. <br /> <br /> <br />This has caused a significant increase in the flood hazard poten- <br /> <br /> <br />tial and in the flood drainage problems upstream from Lowry Air <br /> <br /> <br />Force Base. It also created the potential for failure of Kelly <br /> <br /> <br />Road Dam. <br /> <br />The Highline Canal is currently unable to intercept runoff <br /> <br /> <br />from the upstream area during major flooding. This has increased <br /> <br /> <br />the effective drainage area of Kelly Road Dam from 3.7 to 10.5 <br /> <br /> <br />square miles. Before the recent emergency measures, the emer- <br /> <br /> <br />gency spillway at Kelly Road Dam would have begun to overflow at <br /> <br /> <br />about a 25-year frequency flood and the embankment would have <br /> <br /> <br />been overtopped by a 40-year event. This could have resulted in <br /> <br /> <br />failure of the embankment and the release of all the water behind <br /> <br /> <br />the dam onto the fully developed residential area immediately <br /> <br /> <br />downstream. The emergency measures have reduced the risk of dam <br /> <br /> <br />failure but have not significantly increased the level of <br /> <br /> <br />storage. <br /> <br />Presently, there is no way for low flows from the upper part <br /> <br /> <br />of the basin to cross the Highline Canal except at street cross- <br /> <br /> <br />ings and through a 36-inch bypass from Pond A-B. The con- <br /> <br /> <br />struction of Pond A-B and a concrete-lined flood channel by <br /> <br />14 <br /> <br />. <br />