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Stormwater Stormwater Retrofitting: The Retrofitting: The
Art of Art of OpportunityOpportunity
Prepared by the Center for Prepared by the Center for Watershed ProtectionWatershed Protection
Copyright 2000, CWP
Retrofits are structural Retrofits are structural stormwater management stormwater management measures inserted in an measures inserted in an
urban or ultra-urban urban or ultra-urban landscape where little or landscape where little or
no prior stormwater no prior stormwater controls existed.controls existed.
What Are Stormwater Retrofits?What Are Stormwater Retrofits?
Copyright 2000, CWP
Watershed RestorationWatershed Restoration
Retrofitting should occur within the context of an overall Retrofitting should occur within the context of an overall watershed restoration plan. Typical watershed objectives watershed restoration plan. Typical watershed objectives include the following:include the following:• Stabilizing stream channelsStabilizing stream channels• Improving aquatic habitat within urban streamsImproving aquatic habitat within urban streams• Replacing or enhancing riparian cover along urban streamsReplacing or enhancing riparian cover along urban streams• Protecting a larger resource through pollutant reductionProtecting a larger resource through pollutant reduction• Recolonizing streams with native fishRecolonizing streams with native fish
Copyright 2000, CWP
Copyright 2000, CWPCopyright 2000, CWP
Copyright 2000, CWP
Copyright 2000, CWP
Typical Goals of Stormwater RetrofitsTypical Goals of Stormwater Retrofits
• Minimize accelerated channel Minimize accelerated channel erosionerosion
• Reduce flood peaksReduce flood peaks
• Improve water qualityImprove water quality
• Enhance aquatic habitatEnhance aquatic habitat
• Provide groundwater rechargeProvide groundwater recharge
• Correct past mistakesCorrect past mistakes
Copyright 2000, CWPCopyright 2000, CWP
Copyright 2000, CWPCopyright 2000, CWP
Copyright 2000, CWP
Basic Elements of a Stormwater Basic Elements of a Stormwater Retrofitting Implementation StrategyRetrofitting Implementation Strategy
Step 1. Preliminary Watershed Retrofit InventoryStep 1. Preliminary Watershed Retrofit Inventory
Step 2. Field Assessment of Potential Retrofit SitesStep 2. Field Assessment of Potential Retrofit Sites
Step 3. Prioritize Sites for ImplementationStep 3. Prioritize Sites for Implementation
Step 4. Public Involvement ProcessStep 4. Public Involvement Process
Step 5. Retrofit DesignStep 5. Retrofit Design
Step 6. PermittingStep 6. Permitting
Step 7. Construction InspectionsStep 7. Construction Inspections
Step 8. Maintenance PlanStep 8. Maintenance Plan
Copyright 2000, CWP
Step 1:Step 1: Watershed Retrofit InventoryWatershed Retrofit Inventory
• Identify feasible and appropriate sitesIdentify feasible and appropriate sites
• Complete office exercise, using available mappingComplete office exercise, using available mapping
• Delineate and quantify drainage area to each siteDelineate and quantify drainage area to each site
• Compute a “Target Volume” and measure the site’s Compute a “Target Volume” and measure the site’s available areaavailable area
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Step 1:Step 1: Watershed Retrofit InventoryWatershed Retrofit Inventory(Continued)(Continued)
Useful Materials:Useful Materials:
• Aerial PhotographsAerial Photographs
• Drainage MapsDrainage Maps
• Gas, Water, and Sewer MapsGas, Water, and Sewer Maps
• Zoning/Tax Assessor MapsZoning/Tax Assessor Maps
• Topographic MapsTopographic Maps
Englesby Brook WatershedCopyright 2000, CWP
ENGLESBY BROOKE. Coli Bacteria
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9/30/99 0:00 10/7/99 0:00 10/12/99 0:00 10/20/99 0:00 10/26/99 0:00 11/3/99 0:00
Sample Dates
MP
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UVM Ponds S. Prospect Crescent Shelburne Pine USGS
Copyright 2000, CWP
Copyright 2000, CWP
Step 1:Step 1: Watershed Retrofit InventoryWatershed Retrofit Inventory(Continued)(Continued)
Typical Retrofit Locations:Typical Retrofit Locations:
• Existing BMPs Existing BMPs
• CulvertsCulverts
• Storm Drain OutfallsStorm Drain Outfalls
• Parking LotsParking Lots
• Open SpacesOpen Spaces
• Highway ROWsHighway ROWs
Copyright 2000, CWP
Copyright 2000, CWPCopyright 2000, CWP
Copyright 2000, CWP
Copyright 2000, CWP
Copyright 2000, CWP
Copyright 2000, CWPCopyright 2000, CWP
Copyright 2000, CWPCopyright 2000, CWP
Copyright 2000, CWPCopyright 2000, CWP
Copyright 2000, CWP
Stream Rehabilitation Sites
Storm Drain Retrofits
Stormwater Retrofits
Watts Branch Stormwater
Retrofit and Stream
Rehabilitation Sites
Copyright 2000, CWP
Step 2:Step 2: Field Verification of Candidate SitesField Verification of Candidate Sites
• Complete a ground-truth to determine if the Complete a ground-truth to determine if the contemplated retrofit will workcontemplated retrofit will work
• Prepare a conceptual sketch and take photographsPrepare a conceptual sketch and take photographs
• Use pre-prepared inventory formsUse pre-prepared inventory forms
• Look for pollution prevention opportunities in the fieldLook for pollution prevention opportunities in the field
Copyright 2000, CWP
Copyright 2000, CWP
Copyright 2000, CWP
Step 2:Step 2: Field Verification of Candidate SitesField Verification of Candidate Sites(Continued)(Continued)
Typical Reasons to Reject a Candidate Retrofit Site:Typical Reasons to Reject a Candidate Retrofit Site:• The parking lot identified from aerial photographs is The parking lot identified from aerial photographs is
really a roofreally a roof
• Land use has changed since aerial photographs were Land use has changed since aerial photographs were takentaken
• Open space has an incompatible useOpen space has an incompatible use
• Site elevations make it difficult to convey stormwaterSite elevations make it difficult to convey stormwater
• Soils are inappropriate for the proposed BMP Soils are inappropriate for the proposed BMP
Copyright 2000, CWP
Step 3: Step 3: Prioritize Sites for ImplementationPrioritize Sites for Implementation
• Ensure limited capital budgets are available for Ensure limited capital budgets are available for individual project design and constructionindividual project design and construction
• Ensure target sites meet watershed objectivesEnsure target sites meet watershed objectives
• Consider cost-effectiveness, logistical Consider cost-effectiveness, logistical feasibility, potential for public benefitfeasibility, potential for public benefit
Copyright 2000, CWP
Copyright 2000, CWP
Step 4:Step 4: Public Involvement ProcessPublic Involvement Process
• Critical step if project is to be constructedCritical step if project is to be constructed
• Must involve impacted citizens early and oftenMust involve impacted citizens early and often
• May need to drop projects from further May need to drop projects from further considerationconsideration
• Particularly important if sites are on or near Particularly important if sites are on or near private property or parklandprivate property or parkland
Copyright 2000, CWP
Step 5:Step 5: Retrofit DesignRetrofit Design
• Convert concept to a Convert concept to a construction drawingconstruction drawing
• Requires site analysis Requires site analysis and construction planand construction plan
• Designers need to work Designers need to work within site constraintswithin site constraints
Copyright 2000, CWP
Step 6:Step 6: PermittingPermitting
Permits Required:Permits Required:• Wetlands Wetlands • ForestsForests• FloodplainsFloodplains• Dam SafetyDam Safety• UtilitiesUtilities• RoadwaysRoadways
Strive to minimize impacts and ensure that Strive to minimize impacts and ensure that impacts are offset by the benefits of impacts are offset by the benefits of
project.project.
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Step 7:Step 7: Construction InspectionsConstruction Inspections
• Retrofitting often involves construction of Retrofitting often involves construction of unique or unusual elementsunique or unusual elements
• Practices can be unfamiliar to many Practices can be unfamiliar to many contractorscontractors
• Designer should be active in the construction Designer should be active in the construction processprocess
Copyright 2000, CWP
Step 8:Step 8: Maintenance PlanMaintenance Plan
• Maintenance is often the least practiced Maintenance is often the least practiced component of a stormwater management component of a stormwater management program.program.
• Maintenance is especially important in Maintenance is especially important in retrofit situations.retrofit situations.- - Most retrofits are undersizedMost retrofits are undersized
- - Designers have to balance maintenance Designers have to balance maintenance access and storage volumesaccess and storage volumes
Copyright 2000, CWP
Keys to Successful RetrofittingKeys to Successful Retrofitting
• Follow a systematic and Follow a systematic and straightforward approachstraightforward approach
• Remember that retrofitting is Remember that retrofitting is more of an art than a sciencemore of an art than a science
• Take an approach geared Take an approach geared toward innovationtoward innovation
