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

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100-year floodplain information presents the thalweg elevation which is the elevation of the
channel bottom at its lowest point across the floodplain at that station. The discharge is also
tabulated for each section. The computed water surface elevation, mean channel velocity and
floodplain top width are also shown in the tables.
Alternate Profile information presents the discharge and corresponding water surface elevation
for the 10-year, 50-year and 500-year floods,
The Floodway Information presents the computed floodway data and a definition of floodway
location relative to the channel reference line. The first floodway limits in the table, the 1-foot
floodway data, are the limits of encroachment which result in an increase of not more than one
foot in the total energy grade line due to an approximately equal reduction in the conveyance
on both sides of the channel. The second floodway limits in the table, the 0.5-foot floodway
data, are the limits of encroachment which result in an increase of not more than six inches in
the total energy grade line due to an approximately equal reduction in the conveyance on both
sides of the channel.
The floodway limits shown in the tables are developed for floodplain managers as a guideline
for limiting future encroachment into the floodplain which would further reduce the drainageway
capacity. Preventing such encroachments will help to eliminate future damages in the event of
flooding

Damages in this reach are primarily to structures in the Heritage Square
development. In addition, damage from erosion is also expected due to the
steep channel slopes and high velocities. Some pavement damage from
roadway overtopping is also expected to occur.
Flood odway Table
A table has been prepared which summarizes the results of the hydraulic analyses. This table
relates the cross sectional reference to the mapping, the computed water surface elevations for
several recurrence interval floods, and water surface elevations and limits of allowable
encroachment for two floodways. The table is broken down into four main categories of
information:
1. Reference Information
2. 100-Year Floodplain Information
3. Alternate Profile Information
4. Floodway Information
Reference information relates the various cross-sections to the appropriate channel reach and
the plan and profile sheet number. The section number is related to the stream stationing
which is marked at 500-foot increments along the drainageway baseline or reference line.

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