Stormwater Retrofitting: The Art of Opportunity Prepared by the Center for Watershed Protection

Copyright 2000, CWP Retrofits are structural stormwater management measures inserted in an urban or ultra-urban landscape where little or no prior stormwater controls existed. Retrofits are structural stormwater management measures inserted in an urban or ultra-urban landscape where little or no prior stormwater controls existed. What Are Stormwater Retrofits?

Copyright 2000, CWP Watershed Restoration Retrofitting should occur within the context of an overall watershed restoration plan. Typical watershed objectives 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 reduction Protecting a larger resource through pollutant reduction Recolonizing streams with native fishRecolonizing streams with native fish

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Typical Goals of Stormwater Retrofits Minimize accelerated channel erosion Minimize accelerated channel erosion Reduce flood peaks Reduce flood peaks Improve water quality Improve water quality Enhance aquatic habitat Enhance aquatic habitat Provide groundwater recharge Provide groundwater recharge Correct past mistakes Correct past mistakes

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Basic Elements of a Stormwater Retrofitting Implementation Strategy Step 1. Preliminary Watershed Retrofit Inventory Step 2. Field Assessment of Potential Retrofit Sites Step 3. Prioritize Sites for Implementation Step 4. Public Involvement Process Step 5. Retrofit Design Step 6. Permitting Step 7. Construction Inspections Step 8. Maintenance Plan

Copyright 2000, CWP Step 1:Watershed Retrofit Inventory Identify feasible and appropriate sites Identify feasible and appropriate sites Complete office exercise, using available mapping Complete office exercise, using available mapping Delineate and quantify drainage area to each site Delineate and quantify drainage area to each site Compute a “Target Volume” and measure the site’s available area Compute a “Target Volume” and measure the site’s available area

Copyright 2000, CWP Step 1:Watershed Retrofit Inventory (Continued) Useful Materials: Aerial Photographs Aerial Photographs Drainage Maps Drainage Maps Gas, Water, and Sewer Maps Gas, Water, and Sewer Maps Zoning/Tax Assessor Maps Zoning/Tax Assessor Maps Topographic Maps Topographic Maps

Englesby Brook Watershed Copyright 2000, CWP

Step 1:Watershed Retrofit Inventory (Continued) Typical Retrofit Locations: Existing BMPs Existing BMPs Culverts Culverts Storm Drain Outfalls Storm Drain Outfalls Parking Lots Parking Lots Open Spaces Open Spaces Highway ROWs Highway ROWs

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Stream Rehabilitation Sites Storm Drain Retrofits Stormwater Retrofits Watts Branch Stormwater Retrofit and Stream Rehabilitation Sites

Copyright 2000, CWP Step 2:Field Verification of Candidate Sites Complete a ground-truth to determine if the contemplated retrofit will work Complete a ground-truth to determine if the contemplated retrofit will work Prepare a conceptual sketch and take photographs Prepare a conceptual sketch and take photographs Use pre-prepared inventory forms Use pre-prepared inventory forms Look for pollution prevention opportunities in the field Look for pollution prevention opportunities in the field

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Step 2:Field Verification of Candidate Sites (Continued) Typical Reasons to Reject a Candidate Retrofit Site: The parking lot identified from aerial photographs is really a roof The parking lot identified from aerial photographs is really a roof Land use has changed since aerial photographs were taken Land use has changed since aerial photographs were taken Open space has an incompatible use Open space has an incompatible use Site elevations make it difficult to convey stormwater Site 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: Prioritize Sites for Implementation Ensure limited capital budgets are available for individual project design and construction Ensure limited capital budgets are available for individual project design and construction Ensure target sites meet watershed objectives Ensure target sites meet watershed objectives Consider cost-effectiveness, logistical feasibility, potential for public benefit Consider cost-effectiveness, logistical feasibility, potential for public benefit

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Step 4:Public Involvement Process Critical step if project is to be constructed Critical step if project is to be constructed Must involve impacted citizens early and often Must involve impacted citizens early and often May need to drop projects from further consideration May need to drop projects from further consideration Particularly important if sites are on or near private property or parkland Particularly important if sites are on or near private property or parkland

Copyright 2000, CWP Step 5:Retrofit Design Convert concept to a construction drawing Convert concept to a construction drawing Requires site analysis and construction plan Requires site analysis and construction plan Designers need to work within site constraints Designers need to work within site constraints

Copyright 2000, CWP Step 6:Permitting Permits Required: Wetlands Wetlands Forests Forests Floodplains Floodplains Dam Safety Dam Safety Utilities Utilities Roadways Roadways Strive to minimize impacts and ensure that impacts are offset by the benefits of project.

Copyright 2000, CWP Step 7:Construction Inspections Retrofitting often involves construction of unique or unusual elements Retrofitting often involves construction of unique or unusual elements Practices can be unfamiliar to many contractors Practices can be unfamiliar to many contractors Designer should be active in the construction process Designer should be active in the construction process

Copyright 2000, CWP Step 8:Maintenance Plan Maintenance is often the least practiced component of a stormwater management program. Maintenance is often the least practiced component of a stormwater management program. Maintenance is especially important in retrofit situations. Maintenance is especially important in retrofit situations. - Most retrofits are undersized - Designers have to balance maintenance access and storage volumes

Copyright 2000, CWP Keys to Successful Retrofitting Follow a systematic and straightforward approach Follow a systematic and straightforward approach Remember that retrofitting is more of an art than a science Remember that retrofitting is more of an art than a science Take an approach geared toward innovation Take an approach geared toward innovation