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Mr. Ron Bottoms <br />July 22, 2009 <br />Page 11 of 12 <br />Table 2 <br />Cnmmf ry of C nctc <br />Option lA <br />$ 3,970,350 <br />Option 113 <br />$ 2,863,870 <br />Option 2 <br />$ 3,542,610 <br />Break Out Option 2 in Phases: <br />Option 2, Phase 1 <br />$ 1,116,200 <br />Option 2, Phase 2 <br />$ 2,426,410 <br />Conclusion <br />Option 1 produced reductions along B 112-00-00 and B 112-02-00 with increases along <br />B 109-00-00. The increases along B 109-00-00 are associated with optimizing the amount <br />of detention required, the shape of the detention basin and how it functions, and finally <br />the location of detention within the reach to properly attenuate the increases in flow. <br />Therefore, thorough analysis and design of HCFCD regional detention basin B509-03-00 <br />are key to optimizing its performance which is beyond the scope of services for this <br />work. This is the least expensive option but, all components will need to be constructed <br />at the same time. <br />Option 2 generated results with higher magnitudes than Option 1. This is expected <br />because detention is provided upstream before flows are diverted to receiving streams <br />B112-00-00 and B109-00-00. There is still an increase in flow of 65 cfs generated in <br />B109-00-00 associated with a net decrease in water surface of -0.13. Breaking out <br />Option 2 into phases produces benefits for the interim with reductions in computed water <br />surface elevations and flows associated with the 100-year storm event for both B112-00- <br />00 and Bl12-02-00. Whether Option 2 is constructed in phases or at one time, costs <br />associated with this option fall between Option lA and 1B. On site detention located <br />within City limits adjacent to B 112-00-00 and B 112-02-00 is something the City of La <br />Porte can act on in the interim. <br />Additionally, a detailed hydrologic and hydraulic analysis of the Armand Bayou (B 100- <br />00-00) watershed should be performed to properly model the impacts of changes <br />associated with these options. <br />We recommend Option 2 as a possible project for the City. The overall benefit is greater <br />in reductions to both water surface and flow with the flexibility to perform <br />