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

Presenter

Presentation Notes

45 years ago today, the region suffered a rather large flood event that caused considerable damage in the City of Boulder and other areas. The Colorado General Assembly was considering a bill to establish something called the UDFCD to address regional flood problems that was drafted following a much worse flood that occurred in 1965. One legislator commented that we should approve the bill to stop the rain from falling. The UDFCD Act was signed into law shortly thereafter. Who is UDFCD? Regional agency established by Colorado’s General Assembly in 1969 following a devastating flood in 1965. Partnering with local governments to address multijurisdictional drainage and flood control issues Two-prong approach: 1) fix existing problems and 2) prevent new problems from occurring Steps: Map flood hazards Identify risks within those hazards Develop plans to mitigate hazards and implement those plans Maintain the D&FC facilities that we build and facilities built by others Assist communities with their floodplain and stormwater management activities Provide public information pertaining to floods and how people can protect themselves and their property We operate a local flood warning system in coop w/NWS

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

Presenter

Presentation Notes

Beginning our 36th year of service Briefly review history of FWP Colorado’s most deadly flash flood…1976 Big Thompson…143 fatalities...caused great concern in City of Boulder situated at mouth of Boulder Canyon…lead directly to develop of this early local flood warning program

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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

Presenter

Presentation Notes

Second largest air rescue operation in U.S. history. Katrina #1

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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

Presenter

Presentation Notes

During the flood many questions were being asked by NWS, EM, PS & PW officials, the news media about reports being received. What was really happening and what was going to happen. Streamgages provided the information needed. Both NWS and EM’ credited the program with saving lives. The media picked-up on this idea. This disaster actually turned into a good news day for the FWP.

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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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014 “1,000-year Rainfall”

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

Presenter

Presentation Notes

R&R models for the 2-, 3- and 6-hour design storms all have the 1-hour rainfall in common.

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Presenter

Presentation Notes

As the storm duration wore-on the rareness of the event became more and more apparent. Only one location in Boulder exceeded the 5”/6-hour alarm threshold (SBC @ Road) @ 1:21 AM 9/12 The 3”/2-hour rain rate is slightly greater than the 100-year amount, 1.156*i60m per CUHP Some trivia, maximum ALERT measurements: 24-hour – SBC @ SB Road, 10.7” on 9/12 @0618 6-hour – Montview Park, 6.1” on 9/12 @1238 1-hour – Sand Creek @ Colfax, 2.6” on 9/14 @1700

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1% AEP i10m= 6.1 in/hr

Presenter

Presentation Notes

Do these points represent locations where the rainfall exceeds the 100-year threshold? CORRECT ANSWER: Yes and No, some do some don’t Trick question! CLICK…Remember the 100-yr i10min value (6.1 in/hr) a few slides back…the3 in/hr alarm threshold is only half that value. This particular alarm level is closer to a 5-year than 100-year, and normal indicates the street flooding is occurring. CLICK…here are the points that actually exceeded the 1% AEP value: 2870 South Boulder Road (9.4—7.1—6.0) i5, i10, i15 respectively 9/14 @1521 1000 MGR & 1010 Denver West (8.0—6.4—5.0) 9/9 @1500 1480 3rd Creek at DIA (8.0 for i5 only) 9/9 @1633 810 & 840 Granby @ 6th & FS-12 (8.0—6.6—5.0) on 9/10 @1723 & 9/14 @1625 440 FS-7 Westerly (5.4 for i15 only) on 9/14 @1608 750 Quincy Resv (6.0 for i15 only) on 9/15 @1042 7 sites: Lena & DIA 9/9 TG 9/10 & 9/14 WC 9/14 SBC 9/14

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STREAMGAGES Vitally important on rare occasions

Presenter

Presentation Notes

Not inconspicuous in times like this.

http://videocenter.denverpost.com/services/player/bcpid1149493358001?bckey=AQ~~,AAAAADe65VU~,G496cZ36A_UyJjxj4eEF2Fg5YE08WWhw&bctid=2671275786001

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USGS STREAMGAGE WITH LIVE VIDEO WEBCAM—SEPT. 12, 2013

Fourmile Creek near Orodell in Boulder County, Colorado

Presenter

Presentation Notes

Critical situational awareness was provided by streamgages during the floods, crucial information for managing the emergency and issuing warnings. Streamgages proved their value in many instances like the one shown here.

http://co.water.usgs.gov/webcams/fourmile/

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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

20

14 U

DFCD

Ann

ual

Sem

inar

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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.

Presenter

Presentation Notes

Fourmile Canyon Creek in Boulder County Caused extensive damage in the City of Boulder ($250 million to homes) No fatalities here With media references to the 1976 Big Thompson Canyon flash flood claimed over 140 lives, flood warning systems were credited with saving hundreds of lives in this flood, with only 9 fatalities occurring state-wide. This would not have occurred without the strong partnerships developed over time between forecasters, real-time data providers, emergency managers and many others. USGS streamgages were among the most valuable of assets available to decision-makers during the flood, without which the outcome could have been much worse. Thank you for listening.

9, 2014 never let your guard down – lessons for …...3 alert users group 25 th flood warning...

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