FLOOD09313 - Laserfiche WebLink

Home Browse Search

Commentary on Sheet 8 Item Cost I I I I I I I I I I I I I I I I I I I storm. A major storm would overtop Quincy Avenue with a flow depth of approximately one foot. It is recommended that the 100-year floodplain be regulated and the Denver Water Department and Pinehurst Country Club be notified annually of the potential flood hazard. It is also recommended that the land downstream of the proposed grass-lined channel south of Qui ncy Avenue be regraded. Most of the areas in this reach are the property of the Denver Water Department. There is no plan of development at the present time. The concrete-lined channel from Sheet 7 would continue on this sheet to the Marston Lake access road. A diversion structure would be constructed about 200 feet upstream of the Marston Lake access road to divert water into Ft. Logan Lateral for irrigation. The diversion would consist of a concrete wall with a 4-foot opening and slide gate and a 30-inch CMP, 200 feet long, con- necting the existing pipe. A control gate, which would be opened for low flow and closed for flooding periods would be provided in a manhole. ESTIMATED CONSTRUCTION COSTS A 100-foot long 16l-inch x 101-inch CMP would be installed under the Marston Lake caretaker's house access road to pass a 100-year storm runoff without overtopping the road. At the present time, because the outlet at the road is too small, stormwater would backup and overtop the Marston lake embankment. Other alternatives for the access road crossing should be investigated in final design. Concrete-lined channel - 825 feet Diversion structure with slide gate 30-inch CMP-200 feet Manhole with Control Gate 161-inch x 101-inch CMP - 100 feet Riprap Grass-lined Channel - 1,680 feet 8 Riprap Drop Structures 4 - 65-inch x 40-inch CMP - 225 feet Relocate 12-inch water - 50 feet Relocate 2-inch gas - 50 feet The Marston Water Treatment Plant property does not have a defined channel upstream of Quincy Avenue. The floodplain is caused by a wide sheet flow. A grass-lined channel with trickle channel would be constructed from the Marston lake access road to Quincy Avenue. The proposed channel would follow the access road and Quincy Avenue at the edge of the property for future development consideration. The grass- 1 i ned channel woul d contai n the 100-year storm runoff. Other al ter- natives such as riprap-lined or concrete-line channel should be investigated in final design. Total Construction Costs $ Engineering and Contingencies (35% of Construction Costs) $ Fiscal, Legal and Administrative (5% of Construction Costs) Land Acquisition costs - 3.9 acres At Quincy Avenue, there are major water lines which are obstructions for storm sewer construction, especially for a conduit sized to pass 100-year storm runoff. Currently, storm water would be ponded behind Quincy Avenue until it reaches the top of the roadway. Four 65-inch x 40-inch CMP were proposed under Quincy Avenue to carry as-year Total Costs Annual Maintenance Cost $ 156,800 1,300 6,000 1,800 20,900 3,400 153,700 70,500 51,300 2,500 3,500 471,700 165,100 23,600 120,000* $ 780,400 $ 1,700 *Most of this land is owned by the Denver Water Department. Past prac- tice in implementing flood control projects over publicly owned lands resulted in no land acquisition costs.