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' Arapahoe Ridge subdivisions. Note that the MWE local drainage study <br /> shows a higher discharge in the Wellman at 55th, but they use a higher one <br /> hour local rainfall with larger peak intensities. At 55th Street more flow joins <br /> the Wellman from Dry Creek Ditch No. 2. <br /> • The Wellman east of 55th would spill 700 cfs out of 900 cfs over the north <br /> bank of the Wellman, which would flow north through the golf course. The <br /> remaining 200 cfs returns to South Boulder Creek. <br /> • All of the above flows are likely to be increased as the result of hydrology <br /> model revisions. <br /> LIMITATION AND RECOMMENDATIONS FOR FUTURE STUDY AND <br /> INVESTIGATION <br /> ' This study is an initial study. The following actions are recommended: <br /> 1 . Refine South Boulder Creek and local hydrology including incorporation of <br /> ' realistic rainfall and correction of tributary areas and other physical <br /> parameters to best depict the watershed. This work could include field <br /> surveys to more accurately depict the critical flow splits. <br /> 2. Conduct a floodplain study of the overflow including backwater analysis <br /> using the results of the refined hydrology. Depict the flood limits on the <br /> City of Boulder mapping. While the street flow depths in a 100 year event <br /> ' are relatively shallow (generally 1 .5 to 3.5 feet deep), the public should be <br /> notified of the hazard. <br /> 3. Conduct a collaborative planning effort to mitigate a situation in which all <br /> parties will suffer if the present situation continues. No easy solution exists. <br /> A master plan is needed that would receive the support of most parties. <br /> Such a plan will probably use a variety of hazard management techniques <br /> and physical improvements to address both local drainage and South Boulder <br /> Creek floodplain hazards. <br /> ' I - 5 <br />