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<br />Cost <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />The lOa-year floodplain is to be regulated and it is recommended that the <br />residents within and adjacent to the lOa-year floodplain be notified <br />annually of the potential flood hazards. <br /> <br />COMMENTARY ON SHEET 3 <br /> <br />The improved channel route of South Lakewood Gulch would closely follow the <br /> <br /> <br />existing thalweg from Garrison to Alameda. Contributing flows from Subbasin <br /> <br /> <br />2 would increase from the controlled 5 cfs discharge at Garrison to 240 cfs <br /> <br /> <br />at Alameda. Provision for tributary flow would be made with the side inlet <br /> <br /> <br />structures. <br /> <br />ESTIMATED CONSTRUCTION COST <br /> <br />Item <br /> <br />Grass lined channel below Rockmont Pond <br /> <br />A low flow channel below Garrison would feed into two small farm ponds. <br /> <br /> <br />The existing water surface of these ponds would be maintained however, the <br /> <br /> <br />lOa-year flood water surface would be lowered approximately one-foot due <br /> <br /> <br />to the flow reduction from upstream storage. A grass-lined channel with <br /> <br /> <br />drop structures would be constructed upstream of Alameda. Minor flood <br /> <br /> <br />proofing of an existing structure in this reach will be required. <br /> <br />Raise Rockmont lower pond embankment to <br />elevation 5,520, provide lOa-year capacity <br />concrete spillway with 6'x 6' notch weir and <br />energy dissipator; grouted rock emergency <br />spillway and embankment under-drain system. <br /> <br />Tributary Inflow Structure near Alameda Avenue <br /> <br />Modifications to the Rockmont College Ponds would include raising the em- <br /> <br /> <br />bankment of the lower pond from 5513.4 to 5520.0 feet. The existing embank- <br /> <br /> <br />ment between the two ponds would be preserved. Provisions would be made <br /> <br /> <br />to maintain the normal operating water surface of both lakes. These improve- <br /> <br /> <br />ments will provide approximately 32 acre-feet of usable storage and will <br /> <br /> <br />reduce the lOa-year peak flows from 510 cfs to 130 cfs. Efforts to maintain <br /> <br />the natural habitat below the embankment will be made. A 6' x 6' square <br /> <br /> <br />notch weir and an emergency spillway for the pond will be located to the <br /> <br /> <br />north of the existing outlet. <br /> <br />Grass Lined Channel - Alameda Avenue to <br />Station 130+00 <br /> <br />Low Flow Channel just below Garrison Street <br /> <br />4 Drop Structures <br /> <br />2 - 24~inch RCP's with Drop Boxes <br /> <br />TOTAL CONSTRUCTION COSTS <br /> <br />Engineering and Contingencies (25% Construction <br />Cos ts) <br /> <br />These modifications would be constructed to meet the current design require- <br />ments as established by the State Engineer. The existing facility and <br />structure currently does not meet State Standards. Costs for upgrading the <br />existing embankment to SEa standards are not included in the cost estimate. <br />This upgrading cost will be assumed by the property owner. <br />A grass-lined channel will be used to carry the lOa-year discharge from the <br />ponds to the existing South Lakewood Gulch crossing of Cody Court. Discharges <br />larger than the lOa-year event will follow the historic floodplain of the <br />Gulch. <br /> <br />Fiscal, Legal and Administrative (8% of Total <br />Above) <br /> <br />Land Acquisition Costs <br /> <br />TOTAL COST <br /> <br />Annual Maintenance Cost <br /> <br />$ 12,000 <br />$ 97,000 <br /> <br />$ 2,000 <br />$ 10,000 <br /> <br />$ 2,000 <br />$ 16,000 <br />$ 5,000 <br />$144;000 <br /> <br />$ 36,000 <br /> <br />$ 14;000 <br /> <br />$ 60,000 <br />$ 254;000 <br /> <br />$ <br /> <br />500 <br />