FLOOD10386 ‎(2)‎

• Designation Number: 576
• County: Gilpin
• Community: Black Hawk
• Stream Name: North Clear Creek, Gregory Gulch and Chase Gulch
• Title: Floodplain Information Report - Black Hawk
• Date: 7/1/2004
• Prepared For: Black Hawk and CWCB
• Prepared By: Love and Associates
• Floodplain - Doc Type: Floodplain Report/Masterplan

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PREFACE

The Floodplain Information Report (FIR) is part of a program by the Colorado Water
Conservation Board (CWCB) to aid communities in Colorado in the use of the regulatory
floodplain maps prepared by the Federal Emergency Management Agency (FEMA) in
the community. This Floodplain Information Report provides updated information of
floodplain delineations on existing FEMA maps. In addition, it provides floodplain
management information to guide the local governments in the use of the maps.

The regulated floodplain for the City of Black Hawk is described and mapped within the
Flood Insurance Study (FIS) and on the Flood Insurance Rate Map (FIRM), respectively,
both dated April 1984. Portions of the FIRM were updated by FEMA in 1998, 2002, and
2003. The FIS and FIRM define floodplains for North Clear Creek, Chase Gulch,
Gregory Gulch, and Fourmile Creek using hydraulic analysis. The 1984 FIRM also
identifies approximate floodplains for three tributaries of North Clear Creek, one
tributary of Chase Gulch, and one tributary of Gregory Gulch. These floodplains were
identified using the best information available and were meant to represent floodplain
conditions as they existed at the time of the study.

Subsequent hydraulic analysis identified significant errors in the 1984 hydraulic analysis
and mapping used for the FIRM. An updated hydrologic analysis performed for CWCB
indicated the impact of upstream reservoirs reduce 100-year flood peak estimates of some
streams within the City. These items prompted the City to perform a new hydraulic
analysis of North Clear Creek, Gregory Gulch, and Chase Gulch which has been
submitted to FEMA. In addition, the five tributaries with approximate floodplains were
found to have too small a drainage area to warrant floodplain designation. The floodplain
of the downstream portion of Fourmile Gulch was also revised and its delineation
approved by FEMA. This information has been incorporated into the Floodplain
Information Report.

The Flood Information Report for the City of Black Hawk summarizes updated
floodplain mapping and supporting information to replace floodplain delineations in the
1984 FEMA study. It includes a description of available hydrologic information for
major flooding sources within and adjacent to the City and, for CWCB designation
purposes, supersedes the FIS and the FIRM. In addition, this document provides basic
information about floodplain management and possible alternatives to formulate and
implement floodplain management objectives.

The floodplain information in this document meets the basic technical requirements for
designation and approval by the CWCB. Colorado statutes require local governments
obtain from the CWCB the designation and approval of floodplain information for their
use in regulatory purposes. This document provides a means for the FIS and the FIRM to
meet that statutory objective. As new and more detailed floodplain information becomes
available, floodplain areas shown in this report may change. The CWCB will designate
and approve new information, and rescind old information as appropriate.

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