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CY\ 4-4 I I I I I I I I I I I I I I I I I I I il City of Littleton Massey Draw and SJCD (South) Major Drainageway Planning update Conceptual Design Report February 2006 Table 6 - Estimated Street Overtopping between Carr and Garrison or elevation certificates, however, might show that the bottom floor elevations are above the 100-year floodplain. Reach 4 - Ken Carvl to Pierce: This reach flows through a designated drainage tractO.O, An improved channel with a series of check structures exists between Ken Caryl and Newland. The average slope between the structures is 0.8 percent. The average slope in the remainder of the reach (between Newland and Pierce), which has no check structures, is 2.4 percent. SJCD (South) North Tributary crosses under Kendall in an 80-inch by 53-inch elliptical pipe, under Newland in an 89-inch by 58-inch elliptical pipe, and under Pierce in a 9-foot by 5-foot box culvert. Kendall Street is estimated to overtop 0.2 and 1.4 feet during the 5- and 100-year events, respectively. It is estimated to overtop between the 2- and 5-year storm events. The Newland Street culvert is estimated to overtop 1,0 foot during the 1 OO-year event. It is estimated to overtop between the 10- and 25-year storm events. Streets on SJCD ( South) Tributarv No.1 Estimated 5-Year Estimated 100- Estimated Street Overtopping Year Overtopping Overtopping Return Period Depth (ft) Depth (ft) !Years) Carr Street 1.3 10-25 Codv Street 0,6 1.4 2-5 Dover Street 0.4 1,2 2-5 Estes Court 1,0 10-25 Existing detention ponds with storage of 2.2 acre-feet and 3.6 acre-feet exist upstream of Kipling and Garrison, respectively. Four houses and one out building appear to be in the 100-year floodplain. SJCD (South) Tributarv No.2 Reach 1 - Confluence to Ken Carvl: This reach is characterized by the culvert outlet from the detention pond south of Ken Caryl. It is stable and has an approximate slope of 0.7 percent. The property is owned by the Stony Creek Terrace Home Owners Association. Reach 2- Ken Carvl to Kiolina: An existing detention pond with approximately 1.9 acre-feet of storage comprises the majority of this reach. The property on which this pond exists is owned by Jefferson County, with the western portion of the property under private ownership. SJCD (South) Tributary No. 2 crosses under Ken Caryl in an 8-foot by 4-foot box culvert, 4.3 Floodplain Analysis The 1 OO-year floodplain was developed as part of the Massey Draw and SJCD (South) Major Drainageway Planning Update Flood Hazard Area Delineation (FHAD) (Reference 13). Floodplain and floodway data can be found in the report detailing the FHAD. Reach 3 - Kiolina to Storm Mountain Road: The eastern end of the reach is comprised of a detention pond with 4,9 acre-feet of storage. Property in this reach is owned by Jefferson County and the Ken Caryl Ranch Master Association. Surface drainage west of Jellison Street flows along the street gutters, SJCD (South) Tributary No.2 crosses under Kipling in an 8-foot by-6 foot side-tapered sloping inlet box culvert. Four houses are in the 100-year floodplain. SJCD (South) North Tributarv Reach 1 - South Platte Reservoir to South Platte Canvon Road: Property in this reach is under private ownership within a dedicated drainage easement. Riprap lining and concrete drop structures exist along the channel. The average slope of the channel between the drop structures is 0,5 percent. SJCD (South) North Tributary crosses under South Platte Canyon Road in a double 9-foot by 6-foot concrete box culvert. Reach 2 - South Platte Canvon Road to Sheridan Court: The natural channel in this short reach flows through unincorporated Arapahoe County between the culvert outlet from the West Caryl Avenue area and crosses over private property. The channel has an average slope of 1.7 percent and vertical eroded bank heights of approximately 3 feet exist. Reach 3 - Sheridan Court to Ken Carvl: The drainageway in this reach is along West Caryl Avenue, South Depew Street, South Depew Way, Caryl Place, and South Ames Way. Flow from smaller storm events enters a 6-foot by 5-foot box culvert at Ken Caryl and outlets downstream of Sheridan, The approximate overall slope of the drainage path along the street gutters is 1.5 percent. Seven houses and two out buildings appear to be in the 1 OO-year floodplain. Detailed survey of the house elevations