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Stormwater Mgmt Letter & Doc.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 Methodologies · Alternative Selection Criteria · North Fork Catfish Creek Drainage Basins · Bee Brauch 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: Northwest Arterial to Rosemont Figure 3-!0 North Fork Catfish Drainage Basin Reach: Rosemont to Pennsylvania Figure 3-t 1 North Fork Catfish Drainage Basin Reach: Pennsylvania to University Figure 3-13 North Fork Catfish Drainage Basin Flood Inundation Map - Rosemont to Winnie Figure 3-14 North Fork Catfish Drainage Basin Flood Inundation Map - Winnie to Carter Figure 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 Improvements Figxtre 4-22 Bee Branch Drainage Basin - Proposed Floodway Alternative city of Dubuque, Iowa Drainage Basin Master Plan Executive Summary duly 2001 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 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 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 Ama and the West 32nd Street Drainage Subarea. Finally the entire Bee Branch Drainage Area was evaluated. The attached general location map shoxvs the area of study. Various alternatives were 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 criteria have been provided to several Dubuque consuking engineers for review and comment. These comments ~vill 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 gnide future drainage design and conslraction in the'city of Dubuque. Progress 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 OBJECTIVES Flooding problems in Dubuque can be attributed to two main causes: 1) lack of adequate capacity in storm water conveyance in open-channels, streets and storm servers; 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 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 ukimate development comprehensive land use plan. In several areas, drainage problems were identified for the existing system without consideration of future development. Where problems were identified, alternatives 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 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 Master Plan Executive Summary t July 2001 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 masterplanning activities were suspended until the drainage data became available. A project kick-off meeting ~vas 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 were 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 revie~ving the draft submittals. The standards and criteria have been provided to several Dubuque consuking engineers for review 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. Progress meetings have been conducted in 2000 on June 1, Augnst 3 I, 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 OBJEC i'~VES Flooding problems in Dubuque can be attributed to two main causes: 1) 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 higJa 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 were identified, alternatives 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 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 Master Plan Executive Summary 1 July 2001 EXECUTI'VE SUMMARY The segment of North Fork between the Northwest Arterial and University Avenue was identified as a significant problem area. Numerous residential structures are located within the 100-year flood plain and are relatively Iow 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 structures. 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-I 1. 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 I Modify drainage outlet at Northwest $1,400,000 * Decreases property values at Arterial. Provide additional storage Pann/JFK upstream of Pennsylvania by ,, Changes aesthetics at Pean/JFK excavation, increase channel capacity from Northwest Arterial to Pennsylvania and increase thc capacity of the drainage structures at Rosemont and Keyway. Alternative 2 Provide additional storage upstream of $1,600,000 * Minimum land acquisition costs Northwest Arterial by excavation, ,, Saves trees and maintains aesthetics increase channel capacity from at PenrdJFK Northwest Arterial to Pennsylvania and * Preserves property values at increase the capacity of the drainage PcnrdJ'FK structures at Rosemont and Keyway. · Solves problems close to the source · Best hydrauIic improvement Alternative 3 Provide additional storage upstream of $ 2,4000,000 · Additional costs with no appreciable Northwest Arterial and Pennsylvania by improvement in hydraulics excavation, restrict drainage structure at · Decreases property values at Pennsylvania/JFK and increase channel Penn/JFK capacity, from Northwest Arterial to Pennsylvania and increase the capacity · Changes aesthetics at Penn/JFK of the drainage structures at Rosemont and Keyway. Notes: 1. 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 and maintenance and mitigation costs ~vere not included. Costs based on Iowa Depa~ment of Transportation 1999 unit prices. City of Dubuque, Iowa Drainage Basin Master Plan Executive Summary 2 July 2001 EXECUTIVE SUMMARY It was found that Alternative 3 does not substantially decrease the water surface elevations do~vnstream of the Pennsylvania/JFK 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 100-year floodplain associated with the channel improvements proposed in Alternatives 1 and 2 are shown in Figures 3-13 and 3-14. Alternatives 1 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 cell, 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 site that may be required 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, Kaufmann, Locust, and Downtown 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 showm 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 bas been directed at evaluating storage alternatives in the 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 Alternative 1 Proposed Improvements Construct multiple upstream detention at JFK, pedestrian bridge, and upper Carter. Excavate additional storage at West 32nd detention cell and remove and replace outlet istructure. Purchase properties located xvithin the 100-year flood pool. 1999 Estimated Opinion of Probable Construction Costs~ $5,250.000 City of Dubuque, lowa Drainage Basin Master Plan Executive Summary 3 duly 2001 EXECUTTVE SUMMARY Table ES-2 West 32nd Street Drainage Subarea Improvement Summary Alternative 2 Construct multiple~pstream detention at JFK, pedestrian $4,000,000 bridge, and upper Carter. Increase existing berm elevation to provide additional storage at West 32nd detention cell and remove and replace outlet structure. Purchase properties located within the 100-year flood pool. Alternative 3 Construct one large upstream detention at upper Carter. $4,700,000 Excavate additional storage at West 32nd detention cell and remove and repIace 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 West 32nd detention cell and remove and replace outlet slxucture. Purchase properties located within the 100-year flood pool. Alternative 5 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 cell and remove and replace outlet structure. Purchase properties located within the 100-year flood pool. 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 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 100-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 cell at Upper Carter which ~vill 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 ceil, 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 Executive Summary 4 July 2001 EXECUTI'VE SUMMARY flood inundation for existing conditions., and the condition with the propose&W-est 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 Alternative 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. Although 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, Kanfmann, Locust and West 32nd Street Drainage Subareas 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 akernatives 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 improvements for flood minimization in the Downtown Drainage Subarea. A summary of the structural and non-structural alternatives for flood minimization improvements in the Bee Branch Drainage Basin is listed in Table ES-3. Table ES-3 Bee Branch Drainage Basin Flood Minimization Alternative Improvements Structural Alternatives Non-Structural Alternatives · Open channel floodway · Relief storm sewer · Create upstream detention · Utilize open space upstream detention · Flood proof'nag · Pressure sewer system · Expand 16th Street Detention capacity · Divert West 32nd Street Subarea to the Little Maquoketa · Deep storage/pumping runnel · 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 ~vould save 99% of the homes and businesses from the 100-year floodplain, while requiring the pumhasing 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 445/o of the homes and businesses from the 100- City of Dubuque, lowa Drainage Basin Master Plan Executive Summary 5 July 2001 EXECUTTVE SUMMARY year floodplain. Purchasing or relocation of 13 homes and/or businesses would be. required for this option. Probable construction costs for this option to Alternative 1 are estimated at $6.9 million. The second alternative for the lower Bee Branch Drainage Basin 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 P/an Executive Summary 6 Jul3, 2001 EXECUTI'VE SUMMARY City' of Dubuque, Iowa Drainage Basin Master Plan Executive Summary 7 July 2001 -- i - ~. ~ ~.~O0~ROW f 'T:INNVHOVJ'SO'=Id ~ ,, e ~, EXECUTIVE SUMMARY Bee Branch Drainage Area lO0-Year Flood Inundation Map - Existing Conditions city of Dubuque, Iowa Drainage Basin Master Plan Executive Summary 8 July' 2001 t EXECUT'rVE SUMMARY Bee Branch Drainage Area 100-Year Flood Inundation Map - With West 32nd Street Alternative No. 5 Improvements City of Dubuque, Iowa Drainage Basin Master Plan Executive Summary 9 July 2001