FLOOD10334 ‎(2)‎

• Designation Number: 588
• County: Arapahoe
• County: Jefferson
• Community: Littleton
• Stream Name: Massey Draw and SJCD (South)
• Title: FHAD - Massey Draw and SJCD ‎(South)‎
• Date: 12/1/2005
• Prepared For: Urban Drainage and Flood Control District, Jefferson County, Littleton
• Prepared By: Olsson Associates
• Floodplain - Doc Type: Floodplain Report/Masterplan

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The 100-year profile was exported from HEC-RAS
identify flooding problems

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to HEC-GeoRAS

The drainage structure inventory provided by UOFCO was used to obtain the culvert data needed for
the models, The culvert at C-470 and West Ken Caryl Avenue was determined to have a slope-
tapered inlet. Due to the flow in the stream and the configuration of the culvert inlet, field
measurement was not possible, Construction plans were obtained from CDOT to obtain the
dimensions and elevations needed for the model.

to produce floodplain maps and

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The discharge rates from the baseline hydrology model were used in
discharge rates are presented in Table A-5.

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the hydraulic analysis

The U.S, Army Corps of Engineers HEC-RAS (version 3.1.3, Reference 11) River Analysis System
program and HEC-GeoRAS (version 3,1.1, Reference 12) were used for the analysis. Geometric data
for the HEC-RAS model was obtained using HEC-GeoRAS and a digital elevation model (OEM) that
was generated using the project mapping. This data included the cross sections, river stations, and
channel and overbank lengths, The HEC-GeoRAS data was imported into the HEC-RAS model. The
boundary conditions, culvert data and flow discharges were then added, and the models were run for
the necessary storm events.

These

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A hydraulic analysis was performed to estimate the capacity ofthe existing drainageways and water
surface elevations, The analysis was based on unobstructed flow through culverts and in the
drainageways. The project mapping was used in the analysis and was supplemented by field
investigations, the inventory of drainage structures, and available construction drawings and reports

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Methodology

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4. Hydraulic Analysis

City 0/' Littleton

Flood Hazard Area Delineation
Massey Draw and SJCD (South)
December 2005