FLOOD06961

• County: Jefferson
• Community: Littleton
• Stream Name: Massey Draw and SJCD South
• Basin: South Platte
• Title: Conceptual Design Report for Massey Draw and SJCD ‎(South)‎ Mjor Drainageway Planning Update
• Date: 2/1/2006
• Prepared For: Jefferson County
• Prepared By: Olsson Associates
• Floodplain - Doc Type: Floodplain Report/Masterplan

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8 City of Littleton

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Massey Draw and SJCD (Southl Major Drainageway Planning Update
Conceptual Design Report
February 2006

The 1 OO-year modified baseline model flows are included in Table 5. The effect of the existing
detention on Massey Draw is insignificant. The detention on SJCD (South) reduces the 1 OO-year flows
9 percent to 21 percent, with the most significant decrease immediately downstream of the detention,

Table A-5 in Appendix A presents modified baseline peak flows for all of the UDSWM conveyance
elements in the Massey Draw and SJCD (South) models for the 2-, 5-, 10-,25-,50-, 100-, and 500-
year storm events,

Figures A-10 through A-12 in Appendix A show modified baseline model hydrographs generated by
UDSWM for the 100-year storm at select locations for Massey Draw, SJCD (South), and their
tributaries.

Figure A-13 shows the modified baseline model peak flow versus location (station) for the main
Massey Draw channel and the North Tributary of Massey Draw for the 2-,10-,25-,50- and 100-year
storm events. In the graph of the main channel, the upstream reach of Massey Draw was considered
to be conveyance element 237, just west of the hogback. This point is downstream of two detention
basins and the confluence of several tributaries that convey drainage from the upper portion of the
watershed.

Figure A-14 shows the peak flow versus station for the main channel, North Tributary, and Tributary
Nos, 1 and 2 of SJCD (South).

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