9, 2014 never let your guard down – lessons for …...3 alert users group 25 th flood warning...
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Never Let Your Guard Down – Lessons for ALERT System Managers & Operators from the Colorado Floods of September 2013 Kevin Stewart, Manager Information Services & Flood Warning Program Urban Drainage and Flood Control District, Denver CO
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The Urban Drainage and Flood Control District
Urban Drainage & Flood Control District Flood Warning Program
Serving the greater Denver/Boulder metropolitan area since 1979 in cooperation with NOAA’s National Weather Service
A Federal/Regional/Local Early Warning Partnership
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A Data Rich Environment The ALERT System 2010
2002
2012
1996
1969
2013
2012
2010
195 Rain Gages 99 Streamgages 26 Weather Stations
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THE FLOOD IMPACTS
Colorado’s 9/11 Event September 11-13, 2013 (the 3 worst days)
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The Rescue Operations: by Land…by Water…by Air
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Search & Rescue
1,882 homes destroyed 17,500 damaged 1,000 businesses affected
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18,000 force to leave/26,000 households affected
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Finally Safe
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Damages
200 miles of highway/50 bridges/17 counties
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City of Boulder
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Damages in Longmont
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STATEWIDE: $2-3billion...218 injured…9 fatalities
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SEPTEMBER 14, 2013 HEADLINE 500 people still reported missing
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THE RAINS
September 9-15, 2013
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9/11/2013
Water Vapor Animated
X
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7-day totals approaching 20” exceeded average annual amounts
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Monthly Average Tip Count Summary
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Some very early findings from our NOAA friends September 17, 2013
Estes Park
Lyons
Boulder
Aurora
Longmont
Loveland
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A Rainfall Frequency Plot
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Design Rainfall Comparison Note that the Justice Center ALERT gage did not measure >100-year rainfall
until the storm duration exceeded 3 hours.
Used by all design storms with the Colorado Urban Hydrograph Procedure
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1% AEP i10m= 6.1 in/hr
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STREAMGAGES Vitally important on rare occasions
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USGS STREAMGAGE WITH LIVE VIDEO WEBCAM—SEPT. 12, 2013
Fourmile Creek near Orodell in Boulder County, Colorado
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Stream water level peaks driven by the more intense periods of rainfall…no surprise here
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Fourmile Canyon Creek 36-hour GARR (Gage Adjusted Radar Rainfall)
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Fourmile Canyon Creek Radar-Rainfall 36-hour Time Series—Rains Came in Waves
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Real-Time Rainfall/Runoff Model From GARR estimates for Boulder Creek watershed (September 11-12, 2013)
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What people want to know ASAP after floodwaters recede
Was this a 100-year flood? …a 1000-year flood? …or worse? INITIAL REVELATIONS: 1. Streamgages were of little help with quick answers 2. Rainfall frequency does not equal flood frequency 3. Few understand what they are asking
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Peak Flow Estimates & Corresponding AEP Values AEP results vary widely.
April
15,
2014
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14 U
DFCD
Ann
ual
Sem
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Bad floods happen when we least expect at inconvenient times.
LESSONS
Rainfall frequency never equals flood frequency. People ask difficult questions. Have a good simple answer.
Do not underestimate the importance of streamgages.
Take the time to build relationships.
Be careful where you park your SUV.
Never let your guard down.