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~ Massey Dri;tW ana SJCD (South) Map Dr alnagev..ay Planning Update Conceptual Design Repon February 2006 Dry 0/ Littleton Reaches 6 and 6.1 KiDlina to C-470 and Meadow Ranch Area: Throughout the reach, low flow check structures are proposed to control headcutting. The structures would have a 3-100t maximum drop, with a predicted 0.4% slope between the structures. Acquisition of a drainage easement is recommended. Reach 3 - Allison to Carr: There are no improvements proposed along this reach. Although Kipling Street was estimated to overtop up to 0.7 feet during the 1 DO-year storm, the mapping ~ndicates that a small portion of Kipling Street would be impacted, likely at a lesser depth. No Improvements are proposed. Reach 4 - Carr to Chatfield: A 21.4 acre-foot regional detention basin is proposed upstream of Carr Street to reduce the downstream flow from 1036 to 700 cfs. The flow reduction will eliminate the overtopping at Allison Street and will eliminate the flooding of two houses. Two 6-foot high sloping drop structures are proposed downstream of Chatfield Avenue to drop the channel down to the elevation needed to construct the regional detention basin. The channel downstream of Chatfield is proposed to be reshaped with a bottom width of 20 feet, side slopes of 4:1 and a bottom slope of 0.4%. A drainage easement is recommended between Carr Street and Chatfield Avenue. To prevent the existing flow split and resulting flooding, a levee that conforms to FEMA requirements is proposed to be constructed on the golf course south of the existing driving range detention basin. The levee would direct the 1 OO-year floodwater south of Rockland Drive. A 24-inch reinforced concrete pipe culvert would be constructed through the levee in order to allow low flows to reach existing wetlands east of the proposed levee and north of West Rockland Drive. The owner of the existing Driving Range detention basin would provide full conveyance of the 1 QO-year flow from the detention basin into Massey Draw without the water flowing in an easterly direction north of Rockland Drive. The existing 78.inch diameter reinforced concrete pipe outfall from the detention basin would be extended south through a series of drop manholes to a proposed grass-lined channel that will carry flow south of Rockland Drive to Massey Draw. The channel would have a low-flow channel with a slope of 0.4 percent, bottom with of four feet, depth of two feet, and 2.5:1 (horizontal to vertical) side slopes. The grass-lined channel will have four feet wide overbanks and 4:1 side slopes. A 4.5-foot high drop structure would be constructed in the channel to achieve 0.4 percent slopes. Regrading would lake place between Stations 179+00 and 190+00 along the proposed Massey Draw flow path to maximize the available flow path. A wetland-bottom channel with a bottom width of 100 feet, 2.5:1 side slopes, and a depth of 2 feet would continue east to Kipling Slreet to prevent an increase in water surface elevations due to the additional water flowing south of Rockland Drive. Reach 5 Chatfield 10 Garrison: Low flow check structures are proposed throughout the reach to control headcutting. The structures would have a 3.foot maximum drop, with a predicted 0.4% slope between the structures. A drainage easement is recommended between Dudley Street and Chatfield Avenue. Downstream of Garrison, two 7-foot sloping drop structures are proposed to reduce the channel slope and control erosion. The existing culvert under Garrison Street is proposed to be removed and replaced with a 13 foot x 5 foot reinforced concrete box culvert to eliminate the overtopping and the resulting spilling of water inlo the driveway of townhouses on the east side of Garrison Street. Two 8.foot x 4-foot reinforced concrete box culverts are proposed at Chatfield Avenue to eliminate the street overtopping and at Dudley Street to reduce the overtopping to 0.7 feet. A 6-foot high sloping drop structure is proposed upstream of Dudley Street to drop the channel down to the elevation needed to construct the culvert improvements. The channel downstream of Dudley Street is proposed to be reshaped with a 20-foot bottom width, 4:1 side slopes, and a bottom slope of 0.4%. Select channel banks within the reach are proposed to be stabilized by regrading the banks and providing vegetative and buried rip rap protection. Reach 6 - Garrison to KiDlina: Low flow check structures are proposed to control headcutting. The structures would have a 3-foot maximum drop, with a predicted 0.4% slope between the structures. Reach 7 C-470 to Valley Road: Improvements are proposed to the wall along the north side of the bike path thaI parallels the north side of Massey Draw. The top of the wall would be raised from approximately station 268+80 10 273+60 to prevent flow from spilling onto Ken Caryl Avenue. One foot of freeboard is recommended for the wall. Reach 7 - KiDlinc to Continental Divide Road: Low flow check structures are proposed to control headcutting, if it becomes a problem. The structures would have a 3-foot maximum drop, with a predicted 0.4% slope between the structures. It is recommended that the Owner of the existing detention basin protect the embankment to prevent failure, if it is not protected. North Tributary of Massey Draw SJCD (South) Reach 1 Confluence to Wadsworth: A 6-foot x 8-foot reinforced concrete box culvert is proposed to be installed parallel 10 the existing structure at Wadsworth. The culvert is intended to eliminate the 1 OO-year overtopping at Wadsworth. Reach 1 South Platte Park to S. Platte Canyon Road: Channel improvements are proposed to convey water from the culverts under South Platte Canyon Road to the PMF channel. A 36-inch reinforced concrete pipe (RCP) culvert was constructed to carry Last Chance ditch flow over the channel. Reach 2 Wadsworth to Allison: UDFCD is currently designing a rehabilitation project approximately 200 feet downstream of Allison Street. The improvements will include a 4-foot high sloping drop structure, boulder lined channel and re-alignment of a portion of the drainageway. Reach 2 - South Platte Canyon Road to Depew: Three 14-foot x 8-foot reinforced concrete box culverts are proposed to replace the existing culvert at South Platte Canyon Road to eliminate the street overtopping. A 5.5-foot high sloping drop structure is proposed upstream of South Platte Canyon Road to drop the channel down to the elevation needed to construct the culvert improvements. Additional, low flow check structures and two 5.5-foot high sloping drop structures are proposed to control headcutting. The check structures would have a 3-foot maximum drop, with a predicted 0.4% slope between the structures. Acquisition of a drainage easement is recommended. Reach 3 - Depew to Kendall: Low flow check structures are proposed to control headcutting. The structures would have a 3-foot maximum drop, with a predicted 0.4% slope between the structures. 0\ 6-5