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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stationing, reach, and the

model cross sections to the appropriate channel

Floodway Information

Reference information relates the various
Plan and Profile Drawing number,

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Because of the high degree of development which currently exists in the basin, the future discharges are only
slightly higher than those which might be expected under current conditions. The 100-year floodplain with
improvements, shown on the plan and profile drawings, reflects the effects of proposed plan facilities, Those
facilities are shown on the plans

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bottom at its
50-, 100- and SOO-year floods are also
mean channel velocity, and

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The floodway information presents the computed floodway data and a definition of floodway location relative to the
channel reference line. The floodway limits have been determined to be the limit of encroachment which results in a
total increase of less than one-foot in the total energy grade line due to an approximately equal reduction in the
conveyance on both sides of the channel

Baseline Damages

Estimates of the damage to structures and property were made to allow evaluation of the benefits of possible
drainageway improvements, When a structure's low opening elevation was below the water surface elevation, the
structure was considered to be damaged. The amount of damage was determined using depth-damage relationships
developed by UDFCD or the U.S. Army Corps of Engineers (ACOE).

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Property and structure content values for residential and commercial structures were estimated using available data,
Estimates were also compiled for indirect damages such as debris cleanup, lost sales, and lost tax revenues
Estimates of lost wages for residents of structures damaged were developed for each reach.

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Total direct and indirect damages were computed for each return period. These values were plotted to develop a
damage versus probability relationship. The area under this curve represents the average annual damage. The
average annual baseline damages for each reach were computed by calculating the area under the damage versus
probability curves

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In addition to the damage-probability curves, plots of damage versus discharge were developed for each reach
These damage-discharge curves were then used in subsequent analyses to determine damage reduction due to
improvements. More detail on the baseline damages for the Upper Lena Gulch basin can be found in the Phase A
report.

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Floodway Detennination

Floodway computations were performed for Upper Lena Gulch, Apex Gulch and Pleasant View Tributary. The
floodways are based on equal encroachment in both overbanks resulting in less than a one-foot rise in the energy
grade line elevation above the baseline flood. The baseline is the IOO-year floodplain with existing channel
conditions under future basin development.

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Floodplain/Floodway Table

Table 6 contains a summary of the results of the hydraulic studies. This table relates the cross sectional reference
to the mapping and the computed values for water surface profile elevations. The table is broken down into three
main categories of information as follows

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Location Information

Information

Floodplain

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