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

NTRODUCTION

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Drainageway Description

Lena Gulch has its headwaters in Apex Gulch on the Southeast slopes of Lookout Mountain in Golden, Colorado
From Lookout Mountain, the main stream flows northeast to its confluence with Clear Creek downstream of
Kipling Street in Wheatridge, Colorado.

Tbis Phase B Report presents the results of analyses performed for the Major Drainageway Planning Study for
Upper Lena Gulch. The purpose of the Phase B portion of the study is to perform additional detailed hydrologic and
hydraulic analyses, and to develop preliminary designs and cost estimates of the improvements identified in the
recommended alternative plan from Phase A of the Study. Tbis study was initiated by the project sponsors; the
Urban Drainage and Flood Control District, Jefferson County, and the Cities of Golden and Lakewood. The major
purpose of this study is to evaluate changes in the hydrologic and hydraulic characteristics of Upper Lena Gulch as
an update to a previous Master Plan study completed in June 1975.

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Tbis study deals with the portion of Lena Gulch upstream of Maple Grove Reservoir. Figure 1 shows the study
area location and the basin boundary. Upper Lena Gulch is located in Jefferson County and portions of the cities of
Golden and Lakewood. The mainstem is joined by three major tributaries and several small drainages. Tbis study
includes evaluations of two of the major tributaries, Apex Gulch and the Pleasant View tributary. The third major
tributary, the Green Mountain tributary, has been evaluated previously (Major Drainageway Planning Green
Mountain Area, UDFCD, 1978) and is not included as part of this study.

During Phase A, numerous alternatives were evaluated to identify a reconunended plan that addressed the potential
and past flooding problems along Upper Lena Gulch. Detailed evaluations were made of the flood damages and
costs of alternative improvements to identify the most economically favorable improvement plan for the basin. A
brief summary of those evaluations is included in this report.

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The Apex Gulch tributary joins the mainstem of Upper Lena Gulch in the upper part of the basin in the City of
Golden just downstream of the U.S. Highway 93 crossing. The Pleasant View tributary is located to the north of
Lena Gulch on the south slopes of South Table Mountain. Its confluence with Lena Gulch is downstream of South
Golden Road on the property of the Camp George West Military Post.

Background information on plan components is included in this report as well as sununaries of the detailed
hydrologic and hydraulic analyses performed during the study. The details of the plan components evaluated during
Phase B are contained on plan view and profile drawings included at the end of this report. Also shown on those
drawings are the limits of the 100-year floodplain under future basin development conditions for the existing
drainageway, and for the drainageway with the proposed improvements.

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Tbis study covers approximately 6.5 stream miles: 5.3 miles on the mainstem of Lena Gulch, 0.7 miles on the
Pleasant View tributary, and 0.5 miles along Apex Gulch. Figure 2 shows the location and alignment of the
drainageways and the reach locations as used in this study.

The concepts proposed in this report are intended to serve as the foundation for future drainageway planning, final
design, and improvement implementation.

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The main channel of Lena Gulch follows a northerly alignment along U.S. Highway 40 from near the intersection
with Interstate 70 to a point downstream where it joins with Apex Gulch and crosses through the Hogback. The
channel continues downstream in an easterly direction crossing several streets and mixed residential and commercial
properties in the City of Golden until it empties into a rectangular concrete-lined channel upstream of 6th Avenue,
Downstream of 6th Avenue the channel continues northeasterly through various residential and undeveloped
properties in unincorporated Jefferson County crossing several streets and then crossing under South Golden Road
Below South Golden Road the channel crosses open space in Camp George West and is joined by the Pleasant
View and Green Mountain tributaries just upstream of the Denver West Office Park and 1-70. The drainageway
passes through box culverts under 1-70 and into a series of ponds in the lower portion of the Denver West Office
Park. Downstream of Denver West, the channel meanders through residential areas via varied improved channel
sections and then under Y oungfield Street into Lakewood. From there it continues downstream through residential
properties in an unimproved channel to a crossing under 20th Avenue and into Maple Grove Reservoir at the
downstream end of the study area.

Background

Lena Gulch has been the subject of past studies which have resulted in construction of numerous drainage
improvements to control flooding and reduce damages. The 1975 Master Plan addressed the entire drainageway
from its headwaters to its confluence with Clear Creek. It proposed several alternatives for drainage improvements
including enlarging existing natural channels, enlarging structures at selected street crossings, and providing
detention storage.

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Many of the methods and much of the data used in the hydrologic analysis performed in the previous'Master Plan
have been superseded. The precipitation data used has been updated by the Urban Drainage and Flood Control
District (UDFCD) to incorporate additional historical information not available at the time of that study. In
addition, the computer model used in the previous study to compute runoff hydrographs and peak discharges was
the Massachusetts Institute of Technology Catchment Model (MITCA T). Since that study, the UDFCD has
adopted the Colorado Urban Hydrograph Procedure (CUHP) as the standard methodology for evaluating hydrologic
basin response. The CUHP method has been calibrated to yield results that are more consistent with observed
hydrologic responses in this region. Individual basin runoffhydrographs generated using CUHP are combined and
routed to compute peak discharges using a modified version of the US EP A Stonnwater Management Model
(SWMM) known as UDSWM2.

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