FLOOD06961 - Laserfiche WebLink

Home Browse Search

& Ci(y 0/ Littleton M(!Ss.ey Draw ana ~CD lSOuthl N.ojOf Dralnage"'Nay Pklnnlng Update Conceptual ~1IJfl Report February 2006 2.0 Study Area Description Park, between South Wadsworth Boulevard and South Carr Street. Tributary NO.2 extends from its confluence with SJCD (South) upstream of Ken Caryl Avenue west to Continental Divide Road. The SJCD (South) watershed is fully developed, except for some parcels between South Carr Street and South Kipling Parkway. 2.1 Project Area The study area is located in southern Jefferson County. It is located north of Colorado State Highway C-470 and west of the South Platte River. The study area includes the Massey Draw and SJCO (South) watersheds, and is shown on Figure 1. The area east of South Plane Canyon Road is located in the City of Littleton. The remainder of the study area is located in unincorporated Jefferson and Arapahoe counties. Downstream of South Platte Canyon Road, the Centennial Water and Sanitation District has received approval from the State Engineers Office for construction of the South Platte Reservoir. This project includes a channel designed to convey the Probable Maximum Flood (PMF) from SJCD (South) around the north side of the reservoir to the South Platte River. 2.2 Massey Draw Massey Draw begins at Chatfield Reservoir and extends west approximately three miles west of the hogback and C.470. The North Tributary extends west from its confluence with Massey Draw east of South Wadsworth Boulevard to Simms Street. The watershed covers approximately 9.0 square miles. The study limit is the hogback for Massey Draw and Continental Divide Road for the North Tributary. The Massey Draw watershed is fully developed except for a parcel located southwest of South Carr Street and West Chatfield Avenue and some in-fill parcels located throughout the watershed. Jefferson County, UDFCD and Lockheed Martin are participating in the Massey Draw Watershed and Ecosystem Improvements Pilot Project, which is located between Wadsworth Boulevard and C-470. The project design has been completed and includes bank stabilization, three drop structures, and wetlands habitat improvements to correct bank erosion and reduce the quantity of total phosphorus entering the Chatfield Reservoir. A monitoring program has been designed to provide measurable results by establishing pre.and post-construction trends for both dry and wet weather events, and to determine phosphorus reduction efficiencies for the improvements. The Project Reuse numbers for SJCD (South) is 1-05-6100.01. The watershed limits generally conform to that shown in the Drainage Basin Description Maps (Reference 3). 2.4 Land Use and Characteristics The study area is essentially fully developed, with vacant in-fill parcels scattered throughout the study area. Soils in the watersheds are predominantly hydrologic soils group B, C and D, as defined by the NRCS. These soils are generally characterized by low permeability and high runoff. Hydrologic soils group B soils are also present. The Massey Draw watershed is approximately 7.4 miles long, with an average width of 1.2 miles. Elevations in the Massey Draw watershed range from 5450 to 7880. The average Slope is 11.1 % west of the Hogback and 2.6% east of the Hogback. The SJCD (South) watershed is approximately 4.9 miles long, with an average width of 0.8 miles. Elevations in the SJCD (South) watershed range from 5370 to 5820. The average slope is 1.7%. The County and UDFCD have constructed improvements on Massey Draw and the North Tributary since the Original Plan was completed. Culvert improvements were constructed along South Kipling Parkway in 1988. Culvert and downstream channel improvements were constructed at Carr Street in 1999. Channel stabilization improvements were constructed in 2002 on the North Tributary downstream of Iris Street. Maps showing the watershed boundaries, watershed imperviousness and hydrologic soils groups are presented in Appendix A. 2.5 Reach Description The Project Reuse numbers for Massey Draw and the North Tributary are 1.59.6500-01, -02 and -{)3. The watershed limits generally conform to those shown in the Drainage Basin Description Maps (Reference 3). Detailed descriptions of each reach, as well as discussions of problems and other relevant information, have been included in Section 4.2 in order to limit repetition within the report. Typical cross sections are shown on Sheets 1.38 in Appendix G. 2,6 Flood History 2,3 SJCD (South) SJCD (South) begins at South Platte Park and extends west to approximately South Simms Street. It has three tributaries and covers approximately 3.4 square miles. On August 4, 1999 flash flooding occurred on Massey Draw (Photos 1 and 2) that resulted in stream and localized urban flooding. The peak flow at Carr Street was estimated to be 1100.1200 cfs by taking cross sections and measuring high water marks. The flow was equated to approximately a 10. year storm event based on the Original Plan. Flooding also occurred in the area of the Deer Creek Golf Course/Meadow Ranch development, which was under construction. A flow split was observed at the upstream end of West Rockland Drive. Water was diverted to the north side of West Rockland Drive and overtopped Oak Street and the newly installed culvert. At the time Oak Street and West Rockland Drive had been graded in. Houses had not yet been constructed at the time, so no structures were flooded. The North Tributary extends from its confluence with SJCD (South) downstream of South Platte Canyon Road in a northwesterly direction to Pierce Court. The North Tributary has been improved along its entire length. From Sheridan Court to West Ken Caryl Avenue a portion of the North Tributary flows are conveyed in a 6O.inch pipe. Tributary NO.1 extends from its confluence with SJCD (South) downstream of South Wadsworth Boulevard west to Sangre de Cristo Road. The drainageway has been improved through Coronado 0\. 2'1