FLOOD06632

• County: Rio Blanco
• Community: Rangely
• Stream Name: Rangely area rivers and streams
• Basin: Yampa/White
• Title: Description of Hydraulic Analysis for Section 22 Study at Rangely
• Date: 9/1/1993
• Prepared For: Rangely
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Data ‎(general)‎

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DESCRIPTION OF HYDRAULIC ANALYSIS FOR
SECTION 22 STUDY AT RANGEI.Y, COLOR1\DO
SEPTEMBER 1993

INTRODUCTION

This write-up describes the HEC-2 hydraulic analysis
conducted by the Omaha District for the Section 22 study
conducted for the Town of Rangely, Colorado. This write-up
supplements the main report text and assumes the reader is
familiar with flood plain hydraulic:s and the Corps of
Engineers' HEC-2 computer program.

SOURCE OF DATA

The HEC-2 models used in the Rangely Section 22 study
are based on those created for the 1985 Flood Insurance Study
(FIS) for Rangely. The 1985 FIS was completed for the
Federal Emergency Management Agency by Simons, Li and
Associates, Inc. The HEC-2 input files were obtained in the
form of computer printouts copied onto microfiche. The
microfiche was provided from the archives of Michael Baker,
Jr. Inc., a Technical Evaluation Contractor (TEC) for FEMA.

The Town of Rangely provided blueline copies of the
original FIS work maps. The work maps were plotted on
topographic mapping at a scale of I inch equals 100 feet with
a contour interval of 2 feet. The 1:opographic base mapping
was created by Bell Mapping Company from 198<~ aerial
photography. The cross sections labels shown on the work map
were different from those on the current effe,ctive Flood
Insurance Rate Map for RangelY. Th,~ sections were relabeled
by the TEC.

HEC-2 HYDRAULIC ANALYSIS

All the hydraulic analyses for the Rangely study were
performed using the HEC-2 program for the personal computer,
version of September 1990. The HEC--2 analysis for the 1985
FIS was believed to have been done using an e,arlier version
of HEC-2 for a mainframe type compu1:er, but t:he version of
HEC-2 used is not known. The HEC-2 data from the FIS was
used "as is" and no attempt was made to calibrate the model
with new data. The original FIS cross section geometry,
channel and overbank reach lengths and "n" vallues were used.
The only changes made to the HEC-2 files were, those made to
determine the effect of the existing levee and the potential
extended and improved levee.