Request to Schedule Work Session on Levee Breach Modeling Study Copyrighted
May 21 , 2018
City of Dubuque Action Items # 7.
ITEM TITLE: Request to Schedule Work Session on Levee Breach
Modeling Study
SUMMARY: City Manager requesting that the City Council schedule a
work session for July 23, 2018 on the results of the Levee
Breach Modeling Study.
SUGGESTED DISPOSITION: Suggested Disposition: Receive and File; Council
ATTACHMENTS:
Description Type
Request to Schedule W ork Session on Levee Breach City Manager Memo
Modeling Study-NNM Memo
Staff Memo Staff Memo
THE CITY OF Dubuque
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TO: The Honorable Mayor and City Council Members
FROM: Michael C. Van Milligen, City Manager
SUBJECT: Request to Schedule Work Session on Levee Breach Modeling Study
DATE: May 16, 2018
City Engineer Gus Psihoyos requests the City Council schedule a work session for
July 23, 2018 on the results of the Levee Breach Modeling Study.
I concur with the recommendation and respectfully request Mayor and City Council
approval.
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Mic ael C. Van Milligen��—�
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Attachment
cc: Crenna Brumwell, City Attorney
Teri Goodmann, Assistant City Manager
Cori Burbach, Assistant City Manager
Gus Psihoyos, City Engineer
Dubuque
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TO: Michael C. Van Milligen, City Manage
FROM: Gus Psihoyos, City Engineer ,� ��-=� .
DATE: May 15, 2018
RE: Request for Work Session on Levee Breach Modeling Study
INTRODUCTION
The purpose of this memorandum is to request scheduling a work session on July 23,
2018 with the Mayor and City Council to discuss the results of the levee breach
modeling study.
BACKGROUND
The John C. Culver Floodwall floodwall/levee system was designed to protect the City
of Dubuque from Mississippi River floods. It was authorized by the federal Flood Control
Act of 1962. It consists of a combination of levees and floodwalls along the entire
Dubuque riverfront from the upstream Lock & Dam 11 to the downstream end of the
City near Maus Park. Construction began in 1968 and was completed in 1973. The
improvements associated with the John C. Culver Floodwall flood protection system is
operated and maintained by the City of Dubuque with U.S. Army Corps of Engineers
(USACE) oversight. According to the USACE, as of 2009, the Flood Protection System
"has prevented an estimated $103,955,700 in flood damages."
Dubuque's "Flood Control System" consists of earthen levees (22,500 ft.) and concrete
floodwalls (7,120 ft.), providing protection against a Mississippi River flood that has a
0.5 perc;ent chance of occurring in any given year. The Flood Control System includes
gravity outlets for discharge into the river at low stages and pumping stations and
ponding areas for use when the Mississippi River is high.
Recognizing that Dubuque's Flood Protection System does not eliminate the risk
associated with Mississippi River flooding, the City of Dubuque set aside funding in
FY2014 for the Floodwall Breach Analysis (CIP#7202239). The stated purpose of the
study was to "identify actions that could be taken in the event of a floodwall failure to
reduce the flood and limit property damage." After reaching out to the Rock Island
District of the United States Army Corps of Engineers (District), the City's primary
partner when it comes to the Flood Protection System, the City was informed that the
District had been involved with a similar effort for the City of Muscatine and another was
planned for the City of Cedar Falls. And in August of 2014, the District was able to
secure federal funding to prepare a levee breach computer modeling analysis for the
City of Dubuque.
The USACE created a sophisticated computer model that can predict the depth of
inundation, time to inundation, and inundation paths at critical infrastructure for
hypothetical levee breach scenarios. The main goal of their work was to further
advance the USACE's new computer software tool [HEC-RAS 5.0]. It also helped to
further their mission to ensure that the public understands the risks of "living behind a
levee."
The USACE levee breach analysis was not initiated because of any known imminent
risk of failure to the levee protecting Dubuque, but instead as an effort to improve
emergency planning and communication of the potential risks associated with the levee.
DISCUSSION
In 2015, the City hired engineering consultant HDR to advance the 2-D modeling work
started by the USACE. HDR refined the model by adding break lines to better match
the existing terrain, spatially varied flow path characteristics, and incorporated the
existence of buildings within the model.
With the Fiscal Year 2017 budget, additional funds were established to provide funding
for HDR to further define the depths of inundation, time to inundation, and inundation
paths at critical infrastructure for multiple, hypothetical levee breach scenarios.
The study results provide an understanding of steps that could be taken before, during,
and after a levee breach to mitigate the threat to human safety/health and property.
REQUESTED ACTION
I respectfully request that a work session be scheduled for Monday, July 23, 2018 at
6:00 PM to discuss the results of the levee breach modeling study.
Prepared by Deron Muehring, Civil Engineer
Cc: John Klostermann, Public Works Director
Bob Schiesl, Assistant City Engineer
Deron Muehring, Civil Engineer
Randy Gehl, Public Information Officer