FLOOD11043

• County: Statewide
• Basin: Statewide
• Title: Map Modernization Implementation Plan for Colorado
• Date: 8/1/2002
• Prepared For: FEMA Region 8
• Prepared By: CWCB, UDFCD
• Floodplain - Doc Type: Educational/Technical/Reference Information

Mapping Plan for Colorado

4.0 Meeting Colorado's Goals for Floodplain Mapping

The CWCB staff and the MMIP consultants developed a methodology for prioritizing floodplain mapping
needs for the 64 counties, taking account of the factors that are important to Colorado, in addition to the
FEMA goals discussed above. Three of the seven prioritization parameters were developed with concerns
specific to Colorado in mind.

4.1 Likelihood of Mapping Success

The CWCB believes that it is important to start Colorado's Map Modernization effort in communities
where the likelihood of success is the highest. That means working in counties where it is most likely
that the maps will be of high quality. The MMIP surveys asked communities to indicate whether they
believed there would be local financial support for floodplain mapping. Factors like the answers to that
question, filling out the questionnaires and/or attending the MMIP workshops, past history in preparing
floodplain maps and using them, and CWCB and Urban Drainage & Flood Control District knowledge of
local GIS resources and capabilities all entered into the CWCB rating of each county's likelihood of
success. Scores ranged from 1 to 5. Within the "top 16 counties", four received scores of 4 or higher and
an additional two, received scores of 3.5. CWCB staff expects those communities to participate actively
in ensuring high quality floodplain maps.

4.2 CWCB Rating of Flood Risk

Long-time floodplain managers in Colorado know right away what the years 1921, 1935, 1957, 1965,
1976, 1982, 1984, 1997 and 1999 mean. They refer to flood disasters such as "the '65 flood", the Big
Thompson Flood, the Lawn Lake Flood, and the Fort Collins Spring Creek Flood. They mean severe loss
of life and great property damage. The CWCB staff developed a risk rating that considers the possibility
of property damage and loss of life, due both to existing development and to types of flooding historically
experienced in each community. The rating considered past disasters, including those that resulted in
Presidential Disaster Declarations. Unique hazards, such as erosion, debris flows, and ice jams, were also
considered.

Each community in Colorado (332 total communities) received a score from 0 (not floodprone) to 5
(highest flood hazard risk) from each of three CWCB staff members. Those three scores were averaged
for each community. Then, composite scores were developed for each of the 64 counties. The highest
composite score for any county was 5 and the lowest composite score was 1.7 (average of 3 scores). Of
the "top 16 counties", nine had composite hazard risk ratings of 4 or higher. Utilizing the CWCB
methodology will help identify serious flood hazards in Colorado.

4.3 Wildfire Impacts

Coloradoans will remember the year 2002 as a year of drought and wildfires. Out of the 64 counties in
the state, eleven experienced serious wildfires. Some fires are still burning as this report is completed.
As the Buffalo Creek fire and flood of 1996 demonstrated, floods in watersheds that have experienced
fires can be far more severe than floods in similar watersheds unaffected by fires. While CWCB staff and
the MMIP consultants were preparing the state's mapping plan, professional hydrologists, engineers, and
geologists from the USGS had begun preparing flood hazard (and related debris hazard) maps for selected
bum area watersheds in Colorado. The USGS has no specific plans to integrate these maps into the
county PIS' for those particular counties. The CWCB specifically expects to pursue that integration.
Those eleven counties face specific flood hazards that are different from, and in many respects more
dangerous than the hazards facing the other 53 counties in Colorado.

12/26/2002

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