FLOOD10386

• County: Jefferson
• Community: Golden, Lakewood
• Stream Name: Upper Lena Gulch
• Basin: South Platte
• Title: FHAD - Upper Lena Gulch
• Date: 1/1/1993
• Prepared For: UDFCD
• Prepared By: Boyle Engineering Corporation
• Floodplain - Doc Type: Floodplain Report/Masterplan

500-year

3,900

4,500

7,700

7,800

TABLE 5
500-YEAR PEAK DISCHARGES (cfs)
Location 100-year
Lena Gulch at Hogback 1,770
Lena Gulch at 6th Avenue 2,270
Lena Gulch at 1-70 3,810
nflow to Maple Grove Res. 3,980

Figures 6 through 9 show runoff hydrographs for each recurrence Interval for selected design
points under future basin development.
Results of Hydrologic Analysis
Figures 10 and 11 show discharge versus stream stationing for the 2-, 5-, 10-, 50- and 100-year
floods for the main channel of Upper Lena Gulch, Apex Gulch, and Pleasant View Tributary.
These plots represent peak flows for existing channel conditions under future basin
development.
The peak discharges computed for future basin conditions are used in subsequent hydraulic
analyses to determine limits of flooding and the flood profile along the drainageway.
In addition to the analyses performed during this study to estimate peak discharges and
discharge hydrographs for the 10-,50-, and 100-year frequencies, analyses were performed to
estimate the 500-year frequency peak discharge.
The 500-year frequency peak discharge was estimated by linear extrapolation of log-log plots of
discharge versus exceedance probability for the 2-, 5-, 10-, 50-, and 100-year peak flows under
future basin conditions at selected design points. The estimated peak inflow to Maple Grove
Reservoir for the 500-year frequency event is 7,800 cfs. Table 5 shows the 500-year frequency
peak flows at selected design points.

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