Stormwater Management Work Session 7 20 01CITY OF DUBUQUE, IOWa
MEMORANDUM
July 20, 2001
TO:
FROM:
SUBJECT:
The Honorable Mayor and City Council Members
Michael C. Van Milligen, City Manager
Stormwater Management City Council Worksession
Attached you will find a copy of an executive summary and agenda for Monday night's
worksession regarding stormwater management. The meeting will be held in the
Library Auditorium on the third floor of the Carnegie-Stout Public Library beginning at ·
5:30 p.m. with dinner served on the second floor at 5:00 p.m.
The presentation Monday night will consist of an interactive PowerPoint presentation by
HDR. followed by a question and answer period. HDR will have large visuals depicting
various areas for review.
I am anticipating the meeting taking somewhere between two to three hours.
Michael C. Van Milligen ' ~
M CVM/ksf
A~-tachment
cc: Barry Lindahl, Corporation Counsel
Cindy Steinhauser, Assistant City Manager
Mike Koch, Public Works Director
Gus Psihoyos, Assistant City Engineer
Deron Muehring, Civil Engineer
CiTY OF DUBUQUE, IOWA
MEMORANDUM
July 20, 2001
TO:
Michael C. Van Milligen, City Manager
FROM: Gus Psihoyos, Assistant City Engineer
SUBJECT: Stormwater Management City Council Worksession
Attached you will find a copy of an executive summary and agenda for the Monday
night worksession with the City Council regarding stormwater management.
An interactive PowerPoint presentation will be given by HDR, followed by a
question-and-answer period. Large visuals will be available to aid in the discussion.
It is anticipated that the meeting will last two to three hours. If you have any
questions or comments, please contact me.
GP/ka
Attachs.
City of Dubuque, Iowa
Storm Water Management Plan Project
City Council Working Session Agenda
July 23, 2001
I. Introduction - City Staff
II.
Storm Water Presentation Outline - HDR Engineering, Inc.
· Storm Water Management Overview
· Project Background
· Project Approach
· Project Goals
· Project Methodolo~es
· Alternative Selection Criteria
· North Fork Catfish Creek Drainage Basins
· Bee Branch Drainage Basin
· Possible Funding Sources
III. Questions and Answers
IV. Adjournment
CITY OF DUBUQUE, IOWA
STORMWATER MASTER PLAN
Executive Summary for
Council Worksession -July 23, 2001
EXECUTIVE SUMMARY
List of Figures
General Location Map
Figure 3-9 North Fork Catfish Drainage Basin Reach: North~vest Arteriai to Rosemont
Figure 3-10 North Fork Catfish Drainage Basin Reach: Rosemon~ ~o Peansylvmnia
Figure 3 -11 North Fork Catfish Drainage Basin Reach: Pennsylvania ro Universky
Figure 3-13 North Fork Catfish Drainage Basin Flood Inundation Map - Rosemonr rc Winnie
Figure 3-14 North Fork Catfish Drainage Basin Flood Inundation Map - Winnie to Carter
Figq.tre 4-1 Bee Branch Drainage Basin - Drainage Basin Subareas
Bee Branch Drainage Area 100-Year Flood Inundation Map - Existing Conditions
Figure 4-8 West 32nd Street Drainage Subarea - Detention Site Alternatives
Bee Branch Drainage Area 100-Year Flood Inundation Map - With West 32nd Street Alternative
No. 5 Improvemems
Figure 4-22 Bee Branch Drainage Basin- Proposed Floodway Akemative
City of Dubuque. Iowa Drainage Basin Master Plan
Executive Summary July 2007
EXECUTIVE SUMMARY
PRO3ECT BACKGROUND
The city of Dubuque selected HDR Engineering, Inc. to prepare a stormwater master plan for the city in
October 1998. The city's Geographic Information System (GIS) was in the process of being developed
and the masmrplanning activities were suspended until the drainage data became available. A project
kick-off meeting was conducted on April 6, 2000 to discuss project goals and objectives and designate a
pilot drainage basin. The City's GIS information was completed in May 2000 and HDR began working
on the master planning activities in the pilot study basin, the North Fork of Catfish Creek.
As the project evolved the pilot basin study was expanded to include the entire North Fork of Catfish
Creek Drainage Area and the West 32nd Street Drainage Subarea. Finally the entire Bee Branch
Drainage Area was evaluated. The attached general location map shows the area of study. Various
alternatives ~vere evaluated to reduce the impacts of flooding on the main channel and selected major
tributaries.
In addition to a drainage area masterplan, draft drainage policies and drainage standards/criteria have
been developed. The city staff is reviewing the draft submittals. The standards and 6riteria have been
provided to several Dubuque consulting engineers for revie~v and comment. These comments will be
reviewed'by the Engineering Department and then integrated into a revised draft drainage
standards/criteria document. After it is adopted by the city the drainage standards/criteria will be used to
guide future drainage design and construction in the'city of Dubuque.
ProFess meetings have been conducted in 2000 on June 1, August 3 I, October 25, and December 6 and
in 2001 on May 2 i and July 2 at the offices of the city of Dubuque.
PROJECT GOALS AND OB.]EC;i J. VES
Flooding problems in Dubuque can be attributed to V, vo main causes: I) tack of adequate capacity in
storm water conveyance in open-channels, streets and storm sewers; 2) the inability to discharge into the
Mississippi River during high water levels in the river. The drainage study masterplans will address the
issue of conveyance of storm water in major streams; the identification of existing and future problem
areas that do not meet Dubuque's adopted drainage standards/criteria and the development of
recommendations for solutions to specific problem areas.
This Master Plan addresses existing and projected flooding within the study watershedsk S~ecifically, the
Master Plans identifies the expected future stormwater runoff and hydrology for the drainage areas
considering existing plus proposed land use changes based on the city's ultimate development
comprehensive land use plan. In several areas, drainage problems ;vere identified for the existing system
without consideration of future development. Where problems were identified, akernatives were
developed based on projected future stormwater runoff.
PRELIMINARY FINDINGS
North Fork Catfish Creek
Construction of new or expanded detention storage facilities offers a means of controlling major flood
events to prevent damage to downstream properties and infras~rucV.~re. In the North Fork Catfish Creek
Drainage Basin, the potential to increase detention storage exists along the northern leg of North Fork,
upstream of the No~hwest Arterial and upstream of Pennsylvania./JFK.
City of Dzlbuque, Iowa' Drainage Basin Master Plan
Executive Summary ] July 2001
EXECUTIVE SUMMARY
PRO3ECT BACKGROUND
The city of Dubuque selected HDR Engineering, Inc. to prepare a stormwarer master plan for the city in
October !.998. The city's Geo~aphic Information System (GIS) was in the process of being developed
and the masterplanning activities were suspended until the drainage data became available. A project
kick-off meeting was conducted on April 6, 2000 to discuss project goals and objectives and designate a
pilot drainage basin. The City's GIS information was completed in May 2000 and I-IDR began working
on the master planning activities in the piIot study basin, the North Fork of Catfish Creek.
As the project evolved the pilot basin study was expanded to include the entire North Fork of Catfish
Creek Drainage Area and the West 32nd Street Drainage Subarea. Finally the entire Bee Branch
Drainage Area was evaluated. The attached general location map shows the area of study. Various
alternatives were evaluated to reduce the impacts of flooding on the main channel and selected ma]or
tributaries.
In addition to a drainage area maste~lan, draft drainage policies and drainage standards/criteria have
been developed. The city staff is reviewing the draft submittals. The standards and criteria have been
provided to several Dubuque consulting engineers for review and comment. These comments will be
reviewed by the Engineering Department and then inte~ated into a revised draft drainage
standards/crkeria document. After it is adopted by the city the drainage standards/criteria will be used to
guide future drainage desi~ and construction in the 'city of Dubuque.
Pro~ess meetings have been conducted in 2000 on June 1, August 31, October 25, and December 6 and
in 2001 on May 21 and July 2 at the offices of the city of Dubuque.
PROJECT GOALS AND OB.1E[.i zVES
Flooding problems in Dubuque can be attributed to two main causes: I) lack of adequate capacity in
storm water conveyance in open-channels, streets and storm sewers; 2) the inability to discharge into the
Mississippi River during hi~h water levels in the river. The drainage study masterplans will address the
issue of conveyance of storm water in major streams; the identification of existing and future problem
areas that do not meet Dubuque's adopted drainage standards/criteria and the development of
recommendations for solutions to specific problem areas.
This Master Plan addresses existing and projected flooding within the study watersheds. Specifically, the
Master Plans identifies the expected future stormwater runoff and hydrology for the drainage areas
considering existing plus proposed land use changes based on the city's ultimate development
comprehensive land use plan. In several areas, drainage problems were identified for the existing system
without consideration of future development. Where problems ~vere identified, alternatives were
developed based on projected future srormwater runoff.
PRELIMINARY FINDINGS
North Fork Catfish Creek
Construction of new or expanded detention storage facilities offers a means of controlling major flood
events to prevent damage to downstream properties and infrastructure. In the North Fork Catfish Creek
Drainage Basin, the potential to increase detention storage exists along the northern leg of North Fork,
upstream of the Northwest Arterial and upstream of Pennsylvania/JFK.
'City of Dubuque, lowa Drainage Basin Mastet~ Plan
Executi,~e Summary 1 July 2001
EXECUTIVE SUMMARY
The segment of North Fork bee, veen the Northwest Arterial aad University Avenue was identified as a
significant problem area. Numerous resideatial structures are located within the 100~year flood plain and
are relatively low in relation to the creek and likely incur frequent flooding. It is proposed to improve the
channel capacity, by clearing and grubbing the channel, shaping the channel and increasing the capacity of
the existing drainage s~ructuras.
Three (3) alternatives were evaluated to reduce or prevent damage to private property from the 100-year
flood. These alternatives are depicted in Figures 3-9, 3-10 and 3-1 I. Estimated costs of Akernatives I, 2
and 3 are summarized in Table ES-I.
Table ES-1
North Fork Drainage Basin Channel and Structural Improvement Summary
Alternative Proposed Improvements 1999 Estimated Comments
Opinion of Probable
Construction Costs~
Alternative 1 Modify drainage outlet at Nortlxwe~X S 1,400,000 · Decreases property, values at
Arterial. Provide additional storage Perm/JFK
upstream of'Pennsylvania by * Changes aesthetics at Perm/JFK
excavation, increase channeI capacity
from Northwest Arterial to
Pennsylvania and increase the capacity ~ -
of the drainage strucrm~es at Rosemont
and Keyway.
Alternative 2 ~ Provide additional storage upstream of $1,600,000 * Minimum land acquisition costs
Northwast Arterial by excavation, * Saves trees and maintains aesth~ics
increase channal capacity' from at Penn/JFK
i Northwest Arterial to Pennsylvania and · Preserves property values at
increase the capacity of the drainage PenrffJFK
structures at Rasemont and Keyway.
· Solves problems close to the source
· Best hydranl[c improvement
Alternative 3 Provide additional storage_ upstream of S 2,4000,000 · Additional costs with no appreciable
Northwast Arterial and Pennsylvania by improvement in hydraulics
excavation, restrict drainage structure at · Decreases property values at
Permsylvania/JFK and increase channel Pann/JFK
capacity, fi-om Northwest Arterial to
P~nnsylvania and increase the capacity · Changes aesthetics at Pean/JFK
of the drainage structures at Rosemont
and Keyway.
Notes:
I. Contingencies (25%) were added to account for estimated quantities, unit price adjustments and miscellaneous work
related items. An additional 25% was included for administrative, legal and engineering costs. Right-of-way, operation
prices, and maintenance and mitigation costs were not included. Costs based on I0wa Department of Transportation 1999 unit
City of Dubuque, .rowa
~ecutive Summary 2
Drainage Basin Master Plan
July 200!
EXECUTIVE SUMMARY
It was found that Alternative 3 does not substantially decrease the water surface elevations downs~eam of
the PennsylvaniaiJFK intersection nor does it improve the street drainage at the intersection. The costs
associated with Alternative 3 exceed the resulting benefit of the proposed improvements.
Impacts to the I00-year floodplain associated with the channel improvements proposed in Alternatives 1
and 2 are shown in Figures 3-13 and 3-14. Alternatives I and 2 both include increasing the channel
capacity from Northwest Arterial to Pennsylvania and increasing the capacity of the drainage structures at
Rosemont and Keyway. Although both alternatives remove portions of residential areas from the 100-
year floodplain, the improvements associated with Alternative 2 provide protection to a greater residential
area and contain the 100-year flood to the main channel for longer reaches.
Alternative 2, expansion of the NW Arterial detention ceil, is the recommended option for improvements
to the North Fork Catfish Creek Drainage Basin. This alternative demonstrated the best hydraulic
improvement to the North Fork Catfish Creek system by providing storage in the upper portion of the
basin, and minimum land acquisition costs are associated with this alternative. Although impacts at
Pennsylvania/JFK would be avoided with Alternative 2, some additional excavation at the existing
Pennsylvania detention ske that may be re~luired for borrow purposes would also improve hydraulic
conditions.
Bee Branch
The Bee Branch Drainage Area, as shown in Figure 4-I, includes the West 32nd Street, Kau£mann,
Locust, and Downtovm Drainage Subareas which discharge into the 16th Street Detention Cell. The
primary West 32nd Street conveyance system is an open channel, while in the remaining drainage
subarea's runoff either enters a storm sewer or flows in the streets. The extent of the existing 100~year
flood inundation for the Downtown Drainage Subarea is shown in the attached figure.
In the Bee Branch, the only viable detention storage sites available to store flood flows in upstream areas
are located within the West 32nd Street Drainage Subarea. The emphasis on the study to date has been
directed at evaluating storage akernatives inthe West 32nd Street system. Storing and controlled release
of the upstream runoff to the maximum extent possible permits the downstream storm sewer system to
improve the local drainage during the early stages of a flood event. An initial study of the Bee Branch
storm sewer shows that the local drainage may overwhelm this system and that detention storage in the
upper basins will assist in alleviating flooding problems downstream.
The 100-year return period was used to determine the required storage necessary to reduce the flooding
impacts downstream. Five alternatives were evaluated in the West 32nd Street Drainage Subarea and are
shown in Table ES-2 and Figure 4-8.
Table ES~2
West 32nd Street Drainage Subarea Improvement Summary
Alternative [ Proposed Improvements 1999 Estimated Opinion of Probable
Construction Costs~
Alternative I Construct multiple upstream detention at JFK, pedestrian 55,250.000
bridge, and upper Carter. Excavat~ additional storage at
West 32nd detention cell and remove and rep[ace outlet
structure. Purchase properties located within the 100-year
flood pool.
City of Dubuque, Iowa Drainage Basin Master Plan
F~recutiv¢ Summary 3 July 200I
EXECUTIVE SUMMARY
Table ES-2
West 32nd Street Drainage Subarea Improvement Sam mary
Alternative 2 Construct raultiple~pstream detention at JFK, pedestr~an $4,000,000
bridge, and upper Car~er. [ncraase existing berm elevation to
provide additional storage at West 32ad detention ee!l and
remove and replace outlet stmctura. Purchase properties
located within the 100-year flood pool.
Alternative 3 Construct one large upstream detention at upper Carter. 54,700,000
Excavate additional storage at West 32nd detention ceil and
remove and replace outlet structure. Purchase properties
located within the 100-year flood pool.
Alternative 4 Construct one large upstream detention at upper Carter. $3,500,000
Increase existing berm elevation to provide additional storage
at Wast 32nd detention cell and remove and replace outlet
structure. Purchase properties located within the I00-year
flood pool
Alternative $ Construct one large upstream detention at upper Carter. $4,700,000
Increase existing berm elevation and excavate existing area to
provide additional storage at West 32nd detention ceil and
remove and replace outlet structure. Purchase properties
located within ~e 100-year flood pool.
Notes:
1. Contingencies (25%) were added to account for estimated quantities, unit price adjustments and miscellaneous work.
relate~t items. An additional 25% was included for administrative, legal and engineering cos~:s. Right-of-way, operation
and maintenance and mitigation costs were not included. Costs based on Iowa Department of Transportation 1999 unit
prices.
The proposed detention storage construction on the upper Carter site is located in a natural depression
area and offers the opportunity to store the total upstream t00-year runoff volume, if a control gate is
installed. This structure would be required to be constructed in accordance with the Iowa Department of
Natural Resources, Class 3 dam classification.
It was found that constructing the smaller multiple upstream detention cells are not a favorable option
because the peak discharges are slightly reduced and the peak volumes are unchanged. It is more cost
effective to construct one larger detention ceil at Upper Carter which will have a dramatic impact on the
downstream peak discharges and volumes. Increasing the berm elevation at the West 32nd Street
detention cell is more cost effective than excavation, but since the adjacent homes would be purchased,
excavation remains a viable alternative.
In addition, the analysis shows that the West 32nd Street detention outlet does not adequately regulate the
flows. It is recommended that the existing intake and weir structure be removed and an automatic
controlled gate be installed upstream of the outlet pipe. This gate should operate in conjunction with
sensors on the main Bee Branch storm sewer. The homes located within and surrounding the West 32nd
Street Detention Cell, approximately 15 homes, are located within the existing 100-year flood prone zone
and are located below the elevation of the existing weir. It is recommended to purchase these homes and
restrict development in the 100-year flood zone.
Alternative 5, construction of one large detention cell at Upper Carter with additional excavation and
increased berm elevation of the West 32nd Street detention cell, is the recommended option for
improvements to the West 32nd Street Drainage Subarea. The attached figures compare the 100-year
City of Dubuque, Iowa Drainage Basin Master Plan
Execzttive Suramary 4 July 2001
EXECUTIVE SUMMARY
flood inundation for existing conditions and the condition wkh the proposed.West 32nd Street
improvements from Alternative 5. As shown in these figures, the flood levels are significantly lowered in
the upper portion of the Washin~on Street Subarea with the Akarnafive 5 improvements.
Analysis of the hydrologic and hydraulic characteristics of the Bee Branch Drainage provided numerous
insights into the performance of the existing and proposed systems. Akhough the inlet capacity of the
Bee Branch sewer provides full capacity of the sewer pipes, the capacity of the existing Bee Branch sewer
system is approximately a 7-year return., period event. Flood volumes from the Windsor, Kaufrnann,
Locust and West 32nd Street DrainageSubareas converge upstream of the railroad tracks, which serve as
the primary restriction to flood flows. The only effective upstream detention is in the West 32nd Street
Drainage' Subarea. This detention reduces flooding depths by delaying flood volumes. Since the
improvement of the West 32nd Street Subarea is effective in reducing flooding effects above 24th Street,
solutions for the Downtown Drainage Subarea from 24th Street to the Mississippi River were targeted
with the proposed improvements to the West 32nd Street Subarea included.
The alternatives mentioned for the West 32nd Street Drainage Subarea focus on structural improvements
for flood minimization. However, several non-structural alternatives also exist that may provide more
indirect !mprovements for flood minimization in the Downtown Drainage Subarea. A summary of the
structural and non-structural akernatives for flood minimization improvements in the Bee Branch
Drainage Basin is listed in Table ES-3.
Table ES-3
Bee Branch Drainage Basin Flood ~linimization Alternati'~e Improvements
Structural Alternatives Non-Structural Alternatives
· Open channel floodway
· Relief storm sewer
· Create upstream detention
· Utilize open space upstream detention
· Flood proofing
· Pressure sewer system
· Expand 16ch Street Detention capacity
· Divert West 32nd Street Subarea to the Little
Maquoketa
· Deep storage/pumping turmeI
· Educate/outreach
· Flood warning system
· Floodplain buyout
- Do nothing
From the overall list of alternatives, two primary alternatives were investigated for the lower reach of the
Bee Branch Drainage Basin. The first alternative consisted of constructing a 150-foot wide, open channel
floodway to increase the capacity for the 100-year flood event, as shown in the attached Figure 4-22.
This is the only option that reduces' 100-year flooding in the lower reaches of the Bee Branch.
Construction of this channel from the 16th Street detention cell to 24th Street would save 99% of the
homes and businesses'from the 100-year floodplain, while requiring the purchasing or relocation of
approximately 70 homes and/or businesses. Estimated cost for this alternative is $17.1 million.
A second option to the first alternative was also proposed. This option involved constructing the same
150-foot-wide open channel floodway, but the channel would only be constructed from the 16th Street
detention cell to Garfield Street. This option would save 44% of the homes and businesses from the I00-
City of Dubuque, Iowa Drainage Basin )/faster Plan
Executive Summary 5 July 2001
EXECUTIVE SUMMARY
year floodplain. Purchasing or relocation of I3 homes and/or ~sinesses would be required for this
option. Probable construction costs for this option to Alternative I are estimated at $6.9 million.
The second alternative for the lower Bee Branch Drainage l~asin involves installation of a parallel relief
storm sewer. This alternative would provide protection for the 10-year flood event, but provide only
minimal improvements for flooding depths during the 100-year event. The estimated construction cost of
a single trunk line of storm sewer is $18.7 million.
City of Dubuque, Iowa Drainage Basin Master Plan
Executive Summary 6 July 2001
EXECUTI'VE SUMMARY
City of Dubuqzte, Iowa Drainage Basin Master Plan
Executive Summary 7 July 2001
EXECUT'rVE SUMMARY
~-~; Washinton Street Sub Area lO0-yr Flood Inundation
0.1-0.5
o.5-t ~
2-3
~3-4 N ·
4- 5 1000 0 'i000 2000 Feet ',~
~5+
Bee Branch Drainage Area 100-Year Flood Inundation Map -
Existing Conditions
City of Dubuque, iowa Drainage Basin Master Plan
Executive Summary 8 J~dy 2001
EXECUTI'VE SUMMARY
Wash nton Street Sub Area 100-vr Food nundatlon
Flooding depths with West 32nd Steet improvements installed (feet)
' 0.1 - 0.5
0.5 - 1
~1-2
I 2- 3 N
~3-4
~ 4 - 5 1000 0 1000 2000 Feet
~ 5+ ~ ........
Bee Branch Drainage Area 100-Year Flood Inundation Map -
With West 32nd Street Alternative No. 5 Improvements
City of Dttbuque, Iowa Drainage Basin Master Plan
Executive Sammary 9 July 2001
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