The Flood Threat in Colorado

By Kevin Houck, P.E., CFM

Colorado Water Conservation Board

March 2, 2011

Hello, may I please speak with someone from Emergency Management?

Where and When?

Where and When?

Where and When?

Where and When?

Where and When?

Where and When?

Where and When?

Where and When?

What do these have in common?

Examples of Colorado Flood Events10’s – Cherry Creek in Denver ($161 million, 2 deaths)20’s – Arkansas River at Pueblo ($1.02 billion, 78 deaths)30’s – Monument Creek ($69 million, 18 deaths)50’s – Purgatoire River at Trinidad ($48 million, 2 deaths)60’s – South Platte River in Denver ($2.95 billion, 8 deaths)70’s – Big Thompson Canyon ($114 million, 144 deaths)80’s – Heavy Snowmelt Runoff 1984 ($63 million, 2 deaths)90’s – Fort Collins, Sterling, Lower Arkansas River ($518 million, 6 deaths)00’s – No major disasters, but damages occurred

All values are in 2010 dollars

Since 1900, the AVERAGE annual flood losses in Colorado is over $57 million. 363 lives have been lost.

Examples of Colorado Flood EventsSince Implementation of Floodplain

Management Standards1969 South Platte River Basin ($29 million)**1970 Southwest Colorado ($18 million)**1973 South Platte River in Denver ($531 million)** #31976 Big Thompson Canyon ($116 million, 144 deaths)** #71982 Fall River/Estes Park ($67 million)**1983 North Central Counties ($36 million, 10 deaths)1984 West/Northwest Counties ($64 million)**1995 Western Slope/South Platte ($72 million, 21 deaths)1997 Fort Collins/Eastern Counties ($427 million)** #41999 Colorado Springs/Eastern Counties ($137 million)** #62000’s – No declared disasters, but estimated damages of $136 million

Notes: All values are in 2010 dollars**Denotes Presidential Disaster Declaration

Examples of Recent Colorado Flood Events – Since Floodplain Management Implemented

Since 1910, the AVERAGE annual flood losses in Colorado is about $57 million (2010 $) . 363 lives have

been lost.

Since floodplain management implemented (1968):- 4 of 7 costliest floods in Colorado history occurred- 8 Flood Disasters (Presidential Declarations)

Source: Colorado Flood Hazard Mitigation Plan, 2010

Flooding can be caused or exacerbated by…

Heavy rainSudden snowmeltRain on snowFailed leveesMalfunctioning stormwater systemsBreaks in canals or damsRain on burn scarsDebris flowsEtc.

Colorado Average Annual Precipitation

CWCB Monitors Snowpack by Basin

Status of El Nino/La Nina can produce predictable results

NWS March and Seasonal Forecast

Flood Insurance is an indicator of flood risk

The following communities all have over 200 policies (in order):

BoulderDenverColorado SpringsBoulder CountyLa Plata CountyLarimer CountyArvadaEl Paso CountyJefferson CountyLakewood

Fort CollinsTellurideSteamboat SpringsSterlingAuroraWeld CountyLongmontWinter ParkArapahoe CountyVail

Some Key Flood Points to RememberReally big floods are not that uncommon (usually at least once per decade). Most would not have been anticipated 1-2 weeks in advance even with today's forecasting skill.

Colorado snowmelt is usually well behaved.

Snowmelt floods usually require prolonged very warm temperatures and/or widespread late season snowpack including snow on south facing slopes.

Most of Colorado’s worst floods are rainfall floods.

Floods and drought are not mutually exclusive.

Thank you!For more information, please contact:

Kevin HouckColorado Water Conservation Board(303)866-3441Kevin.houck@state.co.uswww.cwcb.state.co.us**Daily Flood Threat Bulletin Begins May 1st