BOARD00939

• Board Meeting Date: 3/16/2004
• Description: Flood Section - Colorado Floodplain and Stormwater Criteria Manual
• Board Meetings - Doc Type: Other

COLORADO
FLOODPLAIN AND STORMWATER CRITERIA MANUAL

IN THE EVENT THAT CONFLICTS ARISE BETWEEN THE STATEWIDE MANUAL
AND OTHER DRAINAGE MANUALS, THE MANUAL ADOPTED BY THE ENTITY
THAT HAS JURISDICTION OVER THE SUBJECT AREA WILL GOVERN.

2.3 NEW AND REVISED FLOODPLAIN DELINEATIONS

In order to effectively regulate existing and new floodplain improvements and to
reduce the amount of future losses due to flooding, flood hazard areas should be
clearly identified, studied, and delineated. Many drainageways have been analyzed
by various local, state, and federal agencies, and their floodplain delineations can be
found on either the Flood Insurance Rate Maps (FIRMs) published by the Federal
Emergency Management Agency (FEMA) or the community's floodplain maps.
However, throughout the State, numerous floodplain areas that are subject to severe
flooding have not yet been studied, and as new developments occur in these flood
hazard areas, local agencies face the challenge of developing the flood hazard area
information.

PROPOSED OPERATING PRINCIPLE

ALL NEW AND REVISED FLOODPLAIN DELINEATION STUDIES WITHIN THE
STATE OF COLORADO SHOULD BE PREPARED IN ACCORDANCE WITH THE
COLORADO WATER CONSERVATION BOARD (CWCB) "RULES AND
REGULATIONS FOR THE DESIGNATION AND APPROVAL OF FLOODPLAINS
AND OF STORM OR FLOODWATER RUNOFF CHANNELS IN COLORADO". THE
FLOODPLAIN DELINEATION CRITERIA PRESENTED IN THE STATEWIDE
MANUAL ARE THE TECHNICAL GUIDELINES OF THE CWCB RULES AND
REGULATIONS.

2.4 REGULATORY 100-YEAR FLOODPLAINS

Floodplain is the area of land susceptible to being inundated as a result of the
occurrence of a flood event. Floodplain boundaries can be delineated based on two
different analysis approaches: detailed and limited methods. The detailed study
approach should be used when accurate floodplain information including floodplain
limits, water surface elevations and profiles, flood depths and velocities, and
floodway limits are needed for the drainageway being studied. The limited study
method may be used when detailed floodplain information is not necessary. The
limited study usually results in the delineation of approximate flood hazard areas
without base flood elevations,

The floodplain limits resulting from a 1 DO-year flood event should be delineated, as a
minimum, for all floodplain studies. The 1 DO-year peak discharge at a given point is
the estimated peak discharge that has a 1 % probability of occurrence in any given
year.

CHAPTER 2
CWCS PRINCIPLES

SECTION 2
CWCS PROPOSED
OPERATING
PRINCIPLES

PROPOSED OPERATING PRINCIPLE

THE 100-YEAR FLOODPLAINS DELINEATED BY DETAILED OR LIMITED
METHODS ARE CONSIDERED TO BE THE REGULATORY FLOODPLAINS OF
THE STORM OR FLOODWATER RUNOFF CHANNELS IN COLORADO AS
DEFINED IN 37-60-106, COLORADO REVISED STATUES (CRS).

MARCH 2004 - Draft

CWCS PROPOSED
OPERATING PRINCIPLES

CH2-203

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