Work Session - Levee/FloodWall Breach StudyCopyrighted
July 23, 2018
City of Dubuque Work Session - Bottom # 1.
IT EM T IT LE:Levee/Floodwall Breach Study
SUM MARY:City staff and an HDR representative will conduct a work
session / presentation on the Levee/Floodwall Breach
Study.
SUGGEST ED DISPOSIT ION:
ATTACHMENTS:
Description Type
Levee/Floodwall Breach Study-MVM Memo City Manager Memo
Staff Memo Staff Memo
Presentation Outline Supporting Documentation
TO: The Honorable Mayor and City Council Members
FROM: Michael C. Van Milligen, City Manager
SUBJECT: Levee/Floodwall Breach Study
City Council Work Session
DATE: July 19, 2018
City Engineer Gus Psihoyos is transmitting information for the Levee/Floodwall Breach
Study Work Session. City staff and a representative from HDR will make a
presentation.
_____________________________________
Michael C. Van Milligen
MCVM:jh
Attachment
cc: Crenna Brumwell, City Attorney
Teri Goodmann, Assistant City Manager
Cori Burbach, Assistant City Manager
Gus Psihoyos, City Engineer
TO: Michael C. Van Milligen, City Manager
FROM: Gus Psihoyos, City Engineer
John Klostermann, Public Works Director
DATE: July 19, 2018
SUBJECT: Levee/Floodwall Breach Study, City Council Work Session
INTRODUCTION
The purpose of this memorandum is to outline the information to be presented at the City
Council Work Session scheduled for July 23, 2018.
BACKGROUND
The John C. Culver Floodwall system was designed to protect the City of Dubuque from
Mississippi River floods. It was authorized by the federal Flood Control Act of 1962.
Construction began in 1968 and was completed in 1973.
Dubuque’s “Floodwall Protection System” consists of earthen levees (22,500 ft.) and concrete
floodwalls (7,120 ft.) stretching from the upstream Lock & Dam 11 to the downstream end of the
city near Maus Park. It provides protection against a Mississippi River flood up to river stage
28.3. Since the turn of the 20th century, the highest recorded flood stage is 26.81. 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.
Funded and built by the U.S. Army Corps of Engineers (USACE) and operated and maintained
by the City of Dubuque, the Floodwall Protection System protects thousands of properties and
thousands of people from Mississippi River flooding. According to the USACE, the Flood
Protection System “has prevented an estimated $103,955,700 in flood damages as of 2009.”1
In exchange for the USACE agreeing to fund and construct the Flood Protection System, the
City of Dubuque agreed to maintain and operate the floodwall system after completion in
accordance with regulations prescribed by the USACE.
The USACE conducts two types of inspections to help ensure the Flood Protection System is
adequately operated and maintained: periodic inspections and annual inspections. In both
cases, the inspections usually conform to the following process:
• Joint inspection of the Flood Protection System by USACE and City staff;
• USACE provides a report to the City with inspection findings and recommendations;
• Independent inspection and corrective actions are undertaken by the City; and
• City submits a report to USACE outlining actions taken or planned to correct defects
noted in the USACE inspection report.
1 U.S. Army Corps of Engineers - Rock Island District, “Engineering Technical Review Report
Existing Flood Risk Management Levee System – Dubuque, Iowa,” (2010).
2
Based on the inspection, the USACE rates the levee system as Acceptable, Minimally
Acceptable, or Unacceptable.
A Periodic Inspection occurs every five years when the USACE activity is funded. Usually
performed by a third party, the Periodic Inspection is more comprehensive than the Annual
Inspection. The last Periodic Inspection was conducted in 2010 and its findings issued in March
of 2011. The USACE rated the levee system as Minimally Acceptable. According to the USACE,
there were some system elements inspected and rated as Minimally Acceptable and some as
Unacceptable. Moreover, through engineering determinations, they concluded that the
Unacceptable items would not prevent the system from performing as intended during a flood
event.2 The City subsequently addressed the issues within the corrective action period. Based
on the 2017 USACE annual inspection, the Flood Protection System was determined to be
“Acceptable,” the highest rating given.
Recognizing the fact that levees do fail, the City set aside funding in FY2014 for the Floodwall
Breach Analysis. 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 USACE, the City’s primary partner when it comes to the Flood Protection System, the City
was informed that the USACE 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 USACE was
able to secure federal funding to prepare a levee breach analysis for the City of Dubuque.
DISCUSSION
The levee breach study was not initiated because of any known imminent risk of failure to the
levee system that protects Dubuque, but instead as an effort to improve emergency planning
and communication of the potential risks associated with the levee.
The USACE created a sophisticated computer model that can predict the depth of inundation,
time to inundation, and inundation paths at critical locations for hypothetical levee breach
scenarios. The main goal of the USACE’s work was to further advance their new computer
software tool [HEC-RAS 5.0]. But the work also helped to further their mission to ensure that the
public understands the risks of “living behind a levee.” The USACE levee breach analysis
serves as a starting point for additional more detailed analysis of evacuation routes, potential
flood hardening, and overall resiliency planning and design.
The City hired HDR, Inc (HDR), an engineering consultant, to advance the 2-D modeling. While
the USACE model helps to reinforce the idea that there are risks associated with “living behind
a levee,” the work of HDR provided for a model that can be used by the City to identify what
might be done before, during, and after a levee breach to mitigate the threat to human
safety/heath and property.
City staff and a representative from HDR will present more detailed information and lead the
discussion. An outline of the presentation is attached.
REQUESTED ACTION
No action is required. This memo is for informational purposes only.
2 Out-Brief Meeting, Periodic Inspection: Dubuque System, HNTB-Gerwick River Solutions, (2010)
3
Prepared by Deron Muehring
Attach.
Cc: Teri Goodmann, Assistant City Manager
Laura Carstens, Planning Services Manager
Kyle Kritz, Associate Planner
Randy Gehl, Public Information Officer
Deron Muehring, Civil Engineer
Outline
Presentation to City Council on July 23, 2018
Levee Breach Study
1. History of DBQ floodwall system
2. City Operation
3. USACE Oversight
4. USACE Modeling
a. 2-D
b. Five breach locations for one river stage (28.3), a 1,000-year event
5. Des Moines Levee Breach (2008)
6. HDR Modeling
a. HDR efforts compared to USACE
i. Additional breach locations
ii. Multiple river stages
iii. Refined break-lines
iv. Incorporated buildings & streets
v. Statistically reduced infinite number of breach scenarios to most
likely scenarios
b. Researched flood barrier products
c. Model output
i. Video of model running for a particular scenario based on breach
location and river stage
ii. Ultimate depth at various locations
iii. Travel time information
1. Time to 1-foot at location - why important
2. Time to ultimate depth at location (flood proof, future
renovations to consider)
7. How the model output can be utilized
a. Private facility use
i. Pre-breach, floodproof doors/windows
ii. Site Renovations, rebuild facilities to take the information into
account and avoid future flooding
iii. Know how high to place sandbags
iv. Know how much time they would have to evacuate (18 inches of
water can float a car)
b. City use
i. Pre-breach
1. Floodproof doors/windows
2. Site Renovations
ii. During breach
1. Utilization of interior flood barriers to limit the spread of
floodwaters
2. Provide info on availability of streets for evacuation purposes.
(citizens driving out of the area)
3. Provide info on the available time to evacuate a specific facility
8. Introduce Documents
a. Levee Breach Analysis Modeling Report (description of the study)
b. Levee Breach Flood Mitigation Tools (Appendix C)
i. Overview
ii. Example
1. Where can the City erect HESCO barriers?
Where will time allow barriers to be erected?
How long will it take to build: reference table showing
time required and material required
How long before floodwaters reach area: Reference
figure showing time to 0.1 feet and figure showing time to
1 foot of water
2. What streets can be used for evacuation routes and for how
long.
3. Time available to evacuate a facility by vehicle versus boat
9. Next Steps
Levee/Floodwall Breach Analysis
City Council Work Session
July 23, 2018
Agenda
1.History of DBQ floodwall system
2.Operation & Maintenance
3.USACE Oversight
4.Levee Failures
5.USACE Modeling
6.HDR Modeling
7.How the model output can be utilized
8.Introduce Study Documents
9.Next Steps
10.Questions & Discussion
History of Mississippi Flooding
River crested
at 19.80 feet
Flood of May 1916
River crested
at 22.65 feet
Looking NW from 5th & White Streets
Photo courtesy of Pictorial Dubuque: Dubuque’s Greatest Flood
Flood of April 1951
Photos courtesy of Pictorial Dubuque: The Floods Return to Dubuque
Looking west from 16th & Sycamore Streets
River crested at 22.70 feet
Looking east down 17th Street from Washington Street
Dubuque Packing Company
Flood of April 1952
Flood of April 1965
Photo courtesy of TH Media Archives
Temporary sand-bag levees at US20 & S. Locust
River crested at 26.81 feet (Flood of Record)
Levee/Floodwall System: Funding
•1965 Flood was the turning point –community consensus that
a floodwall was needed
•Federal funds sought –but competing with the Vietnam War
and the Space Race
•Congressman John Culver
instrumental in securing
$11 million in federal funds
John C. Culver Floodwall
History of Levee/Floodwall System
Sutton Pool Maus Lake
Port of
Dubuque
Chaplain
Schmitt
Island
East Dubuque, IL
•Construction began in June 1968
•Completed in early 1973
Protected by Dubuque Levee/Floodwall
System designed to provide protection to River Stage 28.3
2011 Analysis showed that the system would remain stable to River
Stage 33, the top of the levee/floodwall system
River Stage 22+ (2011)
Protected by Dubuque Levee/Floodwall
“has prevented
an estimated
$103,955,700 in
flood damages.”
–USACE (2009)
Dubuque Flood Protection System
20,500 feet -Earthen Levees
Dubuque Flood Protection System
20,500 feet -Earthen Levees
900 feet -Concrete Floodwall
Dubuque Flood Protection System
20,500 feet -Earthen Levees
900 feet -Concrete Floodwall
4 -Pumping Stations
Maus Park Pumping Station
Dubuque Flood Protection System
20,500 feet -Earthen Levees
900 feet -Concrete Floodwall
4 -Pumping Stations
10 -Gatewell Structures
Dubuque Flood Protection System
20,500 feet -Earthen Levees
900 feet -Concrete Floodwall
4 -Pumping Stations
10 -Gatewell Structures
10 -Gated Closures
Dubuque Flood Protection System
20,500 feet -Earthen Levees
900 feet -Concrete Floodwall
4 -Pumping Stations
10 -Gatewell Structures
10 -Gated Closures
1-Miter Gated Harbor Closure
Ice Harbor Miter Gate
Dubuque Flood Protection System
20,500 feet -Earthen Levees
900 feet -Concrete Floodwall
4 -Pumping Stations
10 -Gatewell Structures
10 -Gated Closures
1-Miter Gated Harbor Closure
2 -Sandbag Closures
Flood Protection System
Operation & Maintenance
Joint Oversight: Army Corps & City
Project Agreement Requires:
City will operate and maintain
the flood control system as
required by Title 33, Code of
Federal Regulations.
Joint Oversight: Army Corps & City
Requirements:
•All project changes be approved by the Corps of Engineers
•Provide staff to aid Corps required inspections
–Annual Inspections
–Periodic Inspections
•Take corrective actions to correct defects found during inspection
Based on the 2017 annual inspection, the USACE determined the
Levee System to be “Acceptable” which is the highest rating given
Levee Failures
“The people of New
Orleans—and all those
who live in . . . flood-
prone communities
around the country—
must understand and
acknowledge the risks
under which they live.”
What Went Wrong and Why
American Society of Civil Engineers
Hurricane Katrina External Review Panel
Unexpected but result in severe consequences.
In addition to public and private property
damage, major impacts to transportation grid,
power grid, communications, property, and the
public psyche…and it can impact the entire
community –not just the flooded area.
Levee Failures
Levee Failures
Unexpected but result in severe consequences.
In addition to public and private property
damage, major impacts to transportation grid,
power grid, communications, property, and the
public psyche…and it can impact the entire
community –not just the flooded area.
Des Moines in 2008
•Temporary flood barrier construction
started too late
Levee Failures
Unexpected but result in severe consequences.
In addition to public and private property
damage, major impacts to transportation grid,
power grid, communications, property, and the
public psyche…and it can impact the entire
community –not just the flooded area.
Des Moines in 2008
•Temporary flood barrier construction
started too late
•200 homes, 50 businesses, and North High
School were inundated
What can the City do to mitigate the effects of a breach:
•Prior to levee breach?
•During levee breach?
Recognizing that levees fail…
Photo courtesy of Pictorial Dubuque: The Floods Return to Dubuque
What can the City do to mitigate the effects of a breach:
•Prior to levee breach?
•During levee breach?
Recognizing that levees fail…
Photo courtesy of Pictorial Dubuque: The Floods Return to Dubuque
Partnership
Living Behind a Levee:
Evaluation of Urban Levee System Flooding
Scenarios to Support Risk Communications
and Evacuation Planning
Flood Plain Management Services Special Study
Section 206 (PL 86-645) of the 1960 Flood Control Act as Amended
USACE HEC-RAS
2-D Levee Breach Modeling
BUILDING STRONG®
Analysis of failure scenarios, timing, and inundation mapping to
serve as input for stakeholder’s emergency preparedness planning,
and selection of evacuation routes and procedures.
The study was not initiated because of any known imminent risk of
failure to the levee protecting the City of Dubuque.
Study deliverables
History of Levee/Floodwall System
Crescent Community
Health Center
Port of
Dubuque
Chaplain
Schmitt
Island
East Dubuque, IL
BUILDING STRONG®
Crescent Community
Health Center
3 Hours
after Breach
Arrival Time Results for Levee Breach Scenario
Model Output
River Stage 28.3
BUILDING STRONG®
Crescent Community
Health Center
4 Hours
after Breach
Arrival Time Results for Levee Breach Scenario
Model Output
River Stage 28.3
BUILDING STRONG®
Crescent Community
Health Center
Arrival Time Results for Levee Breach Scenario
Maximum depth: 6.6 feet
Time to one foot of water: 4.5 hours
Time to two feet of water: 6.0 hours
Model Output
River Stage 28.3
Development of Flood Fighting Tools
Levee/Floodwall System –Breach Analysis
Refine the model so that it can be used to produce
reliable, flood-fighting information that can be used to
inform decisions during a levee breach
Levee/Floodwall System –Breach Analysis
Refine the model so that it can be used to produce
reliable, flood-fighting information that can be used to
inform decisions during a levee breach
Andy McCoy, PhD, PE
2-D Model Refinement
LiDAR vs Photogrammetry
Port of Dubuque Port of Dubuque
LiDAR picks up more fine-edged elevation
variances such as the HWY 61-151 embankment
that was not recognized in the USACE model
2-D Model Refinement
Added Buildings and Streets
The HDR model recognizes buildings and streets so that it better reflects how water will
propagate through the city.
2-D Model Refinement
Refined Break-lines
Port of Dubuque Port of Dubuque
Break-lines prevent the model from allowing water to free-
flow from one side of the railroad embankment to the other
2-D Model Refinement
Added Buildings and Streets
The HDR model recognizes buildings and streets so that it better reflects how water will
propagate through the city.
This is vital if the City is to rely on the predicted travel
time of floodwaters resulting from a levee breach
2-D Model
Refinement
Additional Breach Locations
1
2
3
4 5
1
2
3
4 5
6
7
2-D Model Refinement
Additional River Stage Scenarios
River Stages
Modeled
28.3
River Stages
Modeled
28.3 > 500-year (Design)
25.5 200-year (2001)
24.3 75-year (1993)
22.1 25-year (2011)
2-D Model Refinement
Additional River Stage Scenarios
River Stages
Modeled
28.3
River Stages
Modeled
28.3 > 500-year (Design)
25.5 200-year (2001)
24.3 75-year (1993)
22.1 25-year (2011)
28 Scenarios
Modeled
2-D Model Refinement
Breach Width Parameters
In addition to the location
of the breach and the river
stage at the time of the
breach, the characteristics
of the breach will also
determine how fast water
floods into the city.
2-D Model Refinement
Breach Width Parameters
In addition to the location
of the breach and the river
stage at the time of the
breach, the characteristics
of the breach will also
determine how fast water
floods into the city.
How large will it get?
2-D Model Refinement
Breach Width Parameters
In addition to the location
of the breach and the river
stage at the time of the
breach, the characteristics
of the breach will also
determine how fast water
floods into the city.
How long will it take?
The Model
Breach location 3
200-year event
floodwall failure
Breach location 3
200-year event
floodwall failure
Information Useful to Individual Property
Plan for the Future
Information Useful to City
Infrastructure Protection
Phase 11 of Bee Branch Watershed Flood Mitigation Project
Before/During a Breach
Install Interior Flood Barriers
Evacuation Planning
During a Breach
Documentation
Engineering Report
Appendix
Flood Breach Mitigation Tools
Levee Breach Mitigation Tools
Example: Breach by Hawthorne Street at River Stage 26.5
Levee Breach Mitigation Tools
Maximum Depth: 8.3 feet
Crescent Community
Health Center
Levee Breach Mitigation Tools
Maximum Depth: 8.3 feet
Crescent Community
Health Center
Levee Breach Mitigation Tools
Time to 1-foot: 8.6 hours
Crescent Community
Health Center
Levee Breach Mitigation Tools
Time to 2-foot: 9.5 hours
Crescent Community
Health Center
Levee Breach Mitigation Tools
Feasibility of Interior Barrier at Fengler: ~2 hours
Levee Breach Mitigation Tools
Time to Construct Interior Barrier: 14 hours/ 6-person crew
Levee Breach Mitigation Tools
Evacuation Using Loras Boulevard: 6.8 hours
Next Steps
1.Determine what and how to communicate emergency response and evacuation information to
the public. GIS and spatial tools could be leveraged to make the information available in a
seamless web-based interface.
2.Develop a GIS interface that pulls together CCTV camera resources to be used for flood
monitoring and model and information confirmation during a breach event.
3.Develop more detailed temporary flood barrier construction plans and specs that would allow
more timely construction and the ability to procure construction services from a contractor
during a breach event.
4.Determine the optimum inventory of HESCO barriers.
5.Develop GIS data sets associated with evacuation areas linked with emergency services
actions to take advantage of developing technology such as reverse 911 and text message
alerts.
Levee/Floodwall Breach Analysis
City Council Work Session
July 23, 2018