FLOOD02650

• County: La Plata
• Stream Name: Animas River
• Basin: San Juan/Dolores
• Title: Hydrology Addendum to FIS La Plata County Unincorporated Areas
• Date: 5/21/2002
• Prepared For: La Plata County
• Prepared By: Montgomery Watson
• Floodplain - Doc Type: Floodplain Report/Masterplan

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PREFACE

This Hydrology Addendum (HA) is part of a program by the Colorado Water Conservation Board
(CWCB) to make approximate floodplain maps prepared by the Federal Emergency Management
Agency (FEMA) easier for local governments to use. This CWCB report provides limited
engineering information to support the approximate delineations on the FEMA maps, and it
provides floodplain management information to guide local governments in the use of the maps.

The effective floodplain information for La Plata County, Colorado, Unincorporated Areas is the
Flood Insurance Study (PIS) of this title dated May 21,2001. The PIS was prepared by FEMA and
contains both detailed and approximate floodplain delineations. The PIS does not include any
engineering information describing the basis of approximate floodplain mapping presented in the
report. The initial purpose of this HA therefore, is to provide La Plata County with limited
supporting information for the approximate floodplain delineations. This HA includes a description
of available hydrologic information for major flooding sources within or adjacent to the county. In
addition, the HA gives the county some basic information about floodplain management and
provides some alternatives that could be considered in formulating and implementing floodplain
management objectives.

A second function of this report is to assure that the PIS meets the basic technical requirements for
designation and approval by the CWCB. Without the inclusion of basic engineering information,
the approximate floodplain delineations shown on the La Plata County Flood Insurance Rate Maps
(FIRMs) cannot qualify for CWCB designation. Colorado statutes require that local governments
obtain from the CWCB the designation and approval of floodplain information for its use in
regulatory purposes. This HA provides a means of meeting that statutory objective. As new and
more detailed floodplain information becomes available, the approximate floodplain areas shown
on the FIRM panels wit! gradually be superseded. The CWCB wit! designate and approve new
information, and rescind old information as appropriate.