FLOOD04641

• County: Denver
• Community: All
• Stream Name: All
• Basin: South Platte
• Title: Proposed Hydrology for use in Hydraulic Analysis of FEMA Flood Studies and Restudies
• Date: 9/1/1989
• Prepared For: State of Colorado
• Prepared By: Resource Consultants
• Floodplain - Doc Type: Educational/Technical/Reference Information

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PROPOSED HYDROLOGY FOR USE IN HYDRAULIC ANALYSIS
OF FEMA FLOOD STUDIES AND RESTUDIES

INTRODUCTION

1.1

Evaluation Procedure

The first step in the evaluation of hydrology for FEMA Flood
Studies was to obtain all available existing data for the
stream basins in question. These included previous Flood
Insuranee StudIes (FIS), Master Drainage Reports (MDR) , Letter
of Map Revisions (LOMR), Letter of Map Amendments (LOMA),
Colorado State HIghway Department culvert design analyses, and
other related reports.

These documents were reviewed on a stream by stream basis to
determine the current appll cabil ity of the hydrology presented
in each. The pertInent criteria Included the exIsting level of
development in each basin, hydrologic modeling parameters and
procedures utilized, and major discrepancies among dIfferent
reports for the same basin.

Field reconnaissance was conducted on all the study stream
reaches to verify existing conditions. Where necessary, return
field investigations were undertaken to satisfy specific
questions arising from the literature review. Locations of the
stream :reaches being studied are shown in Figure 1.1.

In the cases where the reported hydrology was determined
reasonable (according to FEMA study guidelines), a modeling
check of the parameters used was made to verify the resultant
discharges. For those cases with differing levels of
development from existing condItions and/or out of date design
storm criteria, modifications were made to the parameters and a
revised modeling analysis was conducted.

The most detailed evaluations were made for the streams that
exhibited major discharge discrepancies among different
reports:. There were also cases where the City of Colorado
Springs or E1 Paso County questioned the validity of reported
discharges. Under these conditions, a detailed hydrology
reanalysis was undertaken. ThIs included complete reevaluation
of subbasin boundaries and areas, time of eoncentration
estimates, soil curve numbers, streamflow routing, and
detention storage routing.

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