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• Board Meeting Date: 9/18/2007
• Description: Flood Section - State Hazard Mitigation Plan - Flood Chapter Update - FEMA Disaster Mitigation Act of 2000
• Board Meetings - Doc Type: Memo

properties is included in this document with specific information provided on the number
of repetitive loss properties in Colorado on a county-by-county basis. Through the
integration of this information into the planning activities, the capability of Colorado to
be selected for the nationally competitive grant programs should be increased.

SECTION 3: RISK ASSESSMENT

IDENTIFYING FLOOD HAZARDS

A. Description of Flood Hazards Affecting State

The natural hazards affecting the state are described 111 detail in the NHMP 2001
umbrella document. This document focuses on a summary of the flood hazards that
affect the State of Colorado.

A flood is a general and temporary condition of partial or complete inundation of
normally dry land areas from: (1) the overflow of stream banks, (2) the unusual and
rapid accumulation of runoff of surface waters from any source, or (3) mudflows or
the sudden collapse of shoreline land. Flooding results when the flow of water is
greater than the normal carrying capacity of the stream channel. Rate of rise,
magnitude (or peak discharge), duration, and frequency of floods are a function of
specific physiographic characteristics. Generally, the rise in water surface elevation
is quite rapid on small (and steep gradient) streams and slow in large (and flat sloped)
streams. The causes of floods relate directly to the accumulation of water from
precipitation, rapid snowmelt, or the failure of manmade stmctures, such as dams or
levees. Floods caused by precipitation are further classified as coming from:

. Rain in a general storm system
. Rain in a localized intense thunderstorm
. Melting snow
. Rain on melting snow
. Ice jams

Each of these causes results in floods that have distinct characteristics relative to flow
rate, rate of rise, volume, duration, and flood season.

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