FLOOD10385

• County: Jefferson
• Community: Golden, Lakewood
• Stream Name: Upper Lena Gulch
• Basin: South Platte
• Title: Major Drainageway Planning - Upper Lena Gulch - Phase B Report
• Date: 3/1/1994
• Prepared For: UDFCD
• Prepared By: Boyle Engineering Corporation
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Comparing the land use in Upper Lena Gulch under existing and future development conditions, it is evident that
the basin is already highly developed and only relatively small areas of additional development are expected to
occur. Much of the existing undeveloped areas are designated open-space, such as the areas in and around Apex
Gulch, Green Mountain, and South Table Mountain, and are not expected to be developed in the future. As such,
the peak runoff occurring in the basin today is expected to increase only slightly under future development
conditions. Table 5 shows a comparison of the 100-year peak flows at the selected design points under existing and
future basin development, and as estimated for future basin development in the 1975 Master Plan.

The hydrologic model results for the 100-year recurrence interval storm from this study and the 1975 Master Plan
study were compared. The 100-year peak flows computed in this study using the calibrated model agree very
closely with those from the 1975 Master Plan. The calibrated hydrologic model was developed for the ultimate
future basin conditions estimated in the 1975 Master Plan.

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Land use and zoning maps provided by Jefferson County and the Cities of Golden and Lakewood were used to
identify projected ultimate future land use in the basin. Peak discharges for each of the recurrence intervals were
computed by the model for future basin development conditions. Table 4 contains the peak discharges for selected
design points for each of the recurrence intervals under future basin development.

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TABLE 5

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(ers)

100- YEAR PEAK DISCHARGES

Future
Basin
Conditions

Existing
Basin
Conditions

1975 Master
Plan Future
Conditions

Location

TABLE 4

Future Basin Conditions

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1,770

1,770

,810

Lena Gulch at Hogback

Peak Flow Summary At Design Points (ers)

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Lena Gulch at 6th Avenue

100-yr

50-yr

10-yr

br

2:yr

Location

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2,270

2,170

2,220

1,770

1,320

510

370

260

Lena Gulch at Hogback

3,810

3,550

3,750

Lena Gulch at 1-70

3,980

3.690

3.830

Inflow to Maple Grove Res

2,270

1. 740

800

620

420

Lena Gulch at 6th Avenue

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3.810

3.980

3,920

3.080

1,440

1,580

1.120

1,220

730

790

Lena Gulch at 1-70

to Maple Grove Res

Inflow

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In addition, analyses were performed to estimate the 500-year frequency peak discharge for inclusion in the Flood
Hazard Area Delineation (FHAD) report for Upper Lena Gulch produced concurrently with this Master Plan.
Additional detailed information on the hydrologic modeling input, calibration, and results for the Upper Lena Gulch
basin can be found in the Phase A Report.

Figures 5 through 8 show runoff hydrographs for each recurrence interval for selected design points under future
basin development.

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Hydrologic Analysis Results

The hydrographs generated using CUHPE/PC were combined and routed using UDSWM2/PC. The results of the
hydrologic analysis have been plotted on discharge profiles for each of the return periods modeled and are presented
in Figures 9 and 10,

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