1997-03-19_REPORT - M1981302

• Permit No: M1981302
• IBM Index Class Name: Report
• Doc Date: 3/19/1997
• Doc Name: INITIAL RECONNAISSANCE OF DRAINAGE NETWORK AND SOUTH BOULDER CREEKS HYDROLGOY HWY 36 TO APPROXIMATEL
• From: TAGGART ENGINEERING ASSOC INC
• To: URBAN DRAINAGE AND FLOOD CONTROL DISTRICT
• Media Type: D
• Archive: No

• South Boulder Creek at Highway 36. During a 100 year event approximately
2700 cfs out of 5980 cfs would leave the main channel and flow to the
' northwest. In larger storms proportionally more flow would be diverted.
• Along Highway 36 several culverts convey water to the north. The most
significant of these are the Dry Creek Ditch No. 2, the Viele Channel, and the
' Anderson Ditch. Collectively they may carry about 850 to 1200 cfs back to
South Boulder Creek below South Boulder Road.
• Approximately 1800 cfs of the water spilled from South Boulder Creek would
' flood over Highway 36 west of Foothills Parkway and then travel north
through the residential area west of Foothills.
' At the intersection of Foothills Parkway and Baseline Road the flow would
split seven ways. About 600 cfs out of 1800 cfs would go down both lanes
of Foothills Parkway and leave the watershed. Another 260 cfs would flow
on the west side of the Parkway and probably discharge to Wellman Ditch.
570 cfs would follow two paths along the roadway of Baseline Road east,
while another 380 cfs would flow over and under Baseline Road between the
two storage ponds. The east pond would discharge some water to the
culvert under Baseline to the Crossover Ditch and overflow to Baseline Road.
The net effect of all these overflows is estimated to discharge 380 cfs north
to Brooklawn Drive, 270 cfs north to Crescent Drive, and 430 cfs east in the
Crossover Ditch which would join Dry Creek No. 2, with a resultant flow
north of 570 cfs. These flows would also be the result of small splits of
' South Boulder Creek spills from the Anderson Ditch (130 cfs) and remaining
flow in Dry Creek Ditch No. 2 (40 cfs) that did not spill from Dry Creek near
the Viele channel, and local drainage south of Baseline.
• The flow in Dry Creek Ditch No. 2 would probably flood into and along 55th,
and then split three ways, with a minor flow going under the Wellman to Dry
Creek Ditch No. 2 on the golf course and surface flows spilling 500 cfs to
the Wellman west of 55th and 80 cfs east.
• The Wellman Ditch intersects Bear Canyon Creek, where a control structure
directs low flows in the ditch to the east and allows flood flows to go
downstream. However since there is a large box culvert under Foothills, the
Wellman Ditch can convey large flows from Bear Creek to the South Boulder
Creek watershed. Since the Foothills roadway appears to convey flows
north past the Wellman Ditch, the model assumes only the South Boulder
Creek spill in the borrow ditch and the local tributary area runoff west of
Foothills would go into the Wellman (210 cfs). In reality we believe the flow
in the Wellman Ditch would be higher because of Bear Creek flows. The
Wellman is then modeled to collect local drainage and spills from upstream
on the east side of Foothills. A potential flow of 800 to 1 190 cfs would
arrive on the upstream (west) side of 55th plus any Bear Canyon Creek trans
' basin flows.
• About 460 cfs out of 1 190 cfs in the Wellman Ditch west of 55th would
probably overtop the north levee and flow through the Centennial Trails and
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