FLOOD00956

• County: Logan
• Community: Crook
• Stream Name: South Platte
• Title: Hydraulic Analysis for Levee Improvements Along the South Platte at Crook
• Date: 2/17/1987
• Prepared For: State of Colorado
• Prepared By: Muller Engineering Company, Inc.
• Floodplain - Doc Type: Project

February 17, 1987

MULLER ENGINEERING COMPANY, INC.
~---'------- .--.
.. CONSULTING ENGINEEFS
7000 WEST FOURTEENTH AVENUE
LAKEWOOD, COlDRADO 80llS
(303) 2.32-9340

Mr. Larry F. Lang, P.E., Chief
Flood Control and Fl oodpl ai n Management Secti Oil
Colorado Water Conservcltion Board
721 State Centennial Building
1313 Sherman Street
Denver, Colorado 80215

RE: HYDRAULIC ANALYSIS FOR LEVEE IMPROVEMENTS
ALONG THE SOUTH Pl.ATTE RIVER AT CROOK, COLORADO
MEC Project No. 8708-811

Dear Mr. Lang:

The hydraulic analysis for levee improvements along the South Platte River
at Crook, Colorado has been completed. This letter pr'esent~ the results of
the analysis and discusses the methods and assumptions used.

The hydraulic model (HEC-21 util iz~d for this study is the model presented
in the Colorado Department of Highways (COOH) report ent.itled "Hydrology
and Hydraulic Report, Bridge Replacement South of Crook, Colorado, Colorado
State Highway No. 55." This model WvlS run four separate times to reflect
four specific conditions.

CDOH Baseline Model

The model was first run usin!) precisely the same .input data as
were presented in the CDOH report for Alternative 6, the
Recommended Bridge Plan. The results of this run differ from the
CDOH model by 0.01 feet or less in tile 10-,50-, and 100-year
floods for all sections but Section 5, where a difference of
approximately 0.5 feet is evident. Thle discrepancy is attributed
to differences in t.he i nterna 1 ca 1 culillti ons betwE!en the mai nframe
version of HEC-2 used for the CDOH study (updated March, 19821 and
the IBM-PC-XT version of HEC~2 used for this analysis (updated
May, 19841. Section 5 is located 950 feet downstream of the
bridges and the difference in water surfaces does not affect the
hydraulics at the bridges. ihis HEC-Z run serves to verify the
general repeatabil Hy of the results presE!nted I n the CDOH report.

Expanded Baseline Model

The CDOH HEC-2 model was extended both downstream and upst.ream to
serve as the baseline hydraulic mode'i pr.ior to the inclusion of
the levee. Section 0.5 was added approximately 5600 feet
downstream of Section 1 and is based on survey information
supplied by the Colorado Water COllservatioll Board (CWCB). Section
18 was added approximately 1900 feet upstream of Section 17. Its
geometry is the same as Section 17, raised by an amollnt based on

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