FLOOD10351

• County: Statewide
• Community: Statewide
• Title: Statewide River Rehabilitation & Flood Plain Management Needs Inventory
• Date: 12/1/1998
• Prepared For: State of Colorado Department of Natural Resources
• Prepared By: McLaughlin Water Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Table II - 3 - Colorado Declarations and Flood Facts

Recent Major Presidential Disaster Declarations Flood Facts
Year Location Cause CountiesfTownswith 268
1965 Front Range - 33 Counties Intense Flood Prone Areas
(Thunderstorm) Total Flood Insurance 15,203
Rainfall Policies
1969 Front Rance - 15 Counties Sustained Rainfall Population in the 100- 250,000
1970 Southwest Sustained Rainfall year Floodolain
1973 (1) Kersey Dam Failure Homesinthe l(}().year 65,000
(2) Front Range -13 Counties Sustained Rainfall Floodolain
i3i Southwest -13 counties Sustained Rainfall CommerciaVlndustriallBu 15,000
1976 Big Thompson. Front Range - 2 Flash Flooding, sinesses in the 100-year
Counties HeavyrainfaU over Floodnlain
short duration Tolalvalue oftha 16,5
1982 Lawn Lake. Front Range -1 Dam Failure Property in the 1 DO'year Billton
County (Larimerl Floodolain
1984 Western Slope -15 Counties Snowmelt Floods and Cumulative Flood losses 4,5
Mudslides from the Turn of the Billion
1997 Front Range -13 Counties Intense Centu'" to 1999
(Thunderstorm) Miles of Delineated 100- 8000
Rainfall I year Floodnlains

STREAM OmR'OAATION

In addition to the severe flooding threat that exists in Colorado on most major streams and watersheds,
there is on'golng deterioration of streambeds and channels, Some of these channel changes are part of
the natural process; however where there is human intervention, significant damage and losses can be
experienced. For some stream reaches, the flood loss potential is high.

Stream deterioration can be a result of the following activities:
I Streambed Dearadation - Lowering of the existing channel level
. Streambank Erosion - Migration of the high bank to the lett or right across a floodplain
I Streambed Aaaradation - The raising of a streambed or the creation of sandbars within the
conveyance areas
. Sediment Loadino - Increase in stream turbidity, which impacts the water quality, Turbidity is an
accumulation of sediment from watershed development without stormwater detention or from
stream erosion activities,
I Floodolain Land Invasion - Stream migration activity results in the loss of value of land to
agricultural practices, development activities, natural habitat. and transportation systems.

Section II, 7