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<br />i i <br /> <br />The purpose of the study can be summarized as: Perform an in-depth <br />evaluation of the hydrological and hydraulic facets of the storm drainage <br />for the Hidden and Bates lake basins, with primary focus on the major <br />drainageways and flood plains, such that a series of drainage alternatives <br />can be assessed and a recommended program developed. The comparison or <br /> <br />, <br /> <br />, <br /> <br />rating criteria is based, in part, on cost-benefit aspects plus legal and <br /> <br />environmental impact consideration. <br /> <br />Numerous drainage improvement solutions were investigated, ranging from <br /> <br />a minimal protection of about two year frequency to the full 100 year frequency <br /> <br />protection. The improvement facilities investigated include "do-nothing". <br /> <br />grassed and lined channels, storm sewer, detention ponds and dam improve- <br />ments. The improvements for Hidden lake Dam were defined based upon Probable <br />Maximum Precipitation (PMP)-Type B Assumption storm. <br /> <br />The alternative plan chosen is a combination of all the categories <br />excepting the storm sewer solution. The recommended plan (Modified Plan E) <br />specifies no improvements above Hidden lake, improvements to the Hidden <br /> <br />, <br /> <br />lake dam and spillway, extensive channel ization and util ization of existin9 <br />ponds and lakes for the area below Hidden lake. The recommended plan for <br />the Bates lake Basin (Plan B) consists of on-site detention per Arvada <br /> <br />regulations, and the channelization and detention ponding for the lower <br /> <br />reaches of the Bates lake Planning Basin. A summary of the Benefit/Cost <br />Analysis for the Modified Plan E is presented below and includes intangibles. <br /> <br />ITEM <br /> <br />PRESENT WORTH <br />ARVADA ADAMS <br /> <br />Damage Potential* <br />Improvement Costs <br />Benefits <br />Net Benefits <br /> <br />$449,200 <br />300,800 <br />414,000 <br />103,200 <br /> <br />$762,900 <br />652,100 <br />804,400 <br />152,300 <br /> <br />, <br /> <br />, <br /> <br />*potential for reaches with proposed improvements only <br />