Module 2: Bioretention Area Siting and Design Andy Rowe, PE, LEED AP, QSD Cannon

Siting and Design Topics Site Assessment Constraints Opportunities Site Layout Strategies Case Study – 21 st Street, Paso Robles

Site Assessment Develop a series of site assessment maps –Natural features –Built features –Non-physical characteristics Source: LID Technical Guidance Manual for Puget Sound

Natural Site Features Topography –Site visits –As-builts –USGS maps –Topographic surveys Source: United States Geological Survey

Natural Site Features Hydrologic Features –Floodplains (FEMA) –Wetlands –Watercourses –Seeps or springs Sensitive and Restricted Areas –Army Corps –Department of Fish and Game Source: Federal Emergency Management Agency

Natural Site Features Existing Drainage Area Delineation

Natural Site Features NRCS Maps –Soil types –Hydrologic soil groups Source: National Resources Conservation Service

Natural Site Features Geotechnical Assessment –Soil profile –Depth to impervious layer such as bedrock –Depth to groundwater –Geotechnical hazards including landslides –Infiltration rates EPA –Soil contamination –Groundwater contamination

Natural Site Features Vegetative and Tree Cover –Site visits –Aerial photography –Topographic surveys –Arborist reports Source: Google Earth

Built Site Features Sources –GIS –As-builts –Topographic surveys –USA dig Drainage Infrastructure Buildings and Walls Impervious Areas Landscape Areas Utilities Groundwater Wells for Drinking Water

Non-Physical Characteristics Easements Covenants Zoning/Land Use Development Code Setbacks from Buildings and Property Lines Open Space and Landscaping Requirements Historical Designations Other Pertinent Overlays

Bioretention Constraints Impermeable Soils Groundwater Pollution or Contaminated Soils High Groundwater Impervious Soil Layer Vector Issues Geotechnical Instability Steep Slopes Coastal Bluffs When should an underdrain be used?

Bioretention Constraints Infill, Redevelopment and High Density Land Buildings to Remain Utility Locations

Bioretention Constraints Incompatibility with Surrounding Drainage System Flooding and Overflow Routes Tree Preservation ADA Considerations Safety Hydrologic Features Sensitive Areas Drinking Water Wells

Bioretention Opportunities Permeable Soils Uncompacted Soils (Undeveloped Areas) Mild Slopes and Depressions

Bioretention Opportunities Intersection Bulb-Outs Source: LID Technical Guidance Manual for Puget Sound

Bioretention Opportunities Cul-de-Sacs and Loop Roads Roadway Medians Source: LID Technical Guidance Manual for Puget Sound

Bioretention Opportunities Buffer Between Curb and Sidewalk Source: LID Technical Guidance Manual for Puget Sound

Bioretention Opportunities Required Landscaping and Open Space Setbacks and Easements Source: bluegreenbldg.org

Bioretention Opportunities Combine Conveyance with Bioretention –Sinuosity

Bioretention Opportunities Distribute Bioretention Areas Across the Site

Site Layout Strategies Identify the Development Envelope and Protected Areas Limit Clearing and Grading of Native Vegetation –Incorporate established trees Prevent Disturbance of Natural Drainage Features Concentrate Development on Least Permeable Soils Plan Construction to Minimize Compaction of Permeable Soils Iterate Design

Site Layout Strategies Cluster Development Source: LID Technical Guidance Manual for Puget Sound

Site Layout Strategies Dispersal of Runoff to Pervious Areas –Direct runoff from impervious to pervious areas –Disconnect downspouts Source: bluegreenbldg.org Source: LID Manual for Southern California

Site Layout Strategies Measures to Limit Imperviousness and Create Space for Bioretention –Compact, taller structures –Cluster development –Narrower streets and lanes –Reduce number of cross streets –Smaller parking lots (fewer stalls, smaller stalls, more efficient lanes) –Shared driveways

Site Layout Strategies Other Considerations –Locate bioretention areas away from high pedestrian traffic or provide elevated walkways –Sight distance –Accessibility for maintenance –Separate clean and dirty water –Complete streets Pedestrian and ADA considerations Bicycles Parking Traffic Calming

Case Study: 21 st St, Paso Robles Source: City of Paso Robles

Case Study: 21 st St, Paso Robles

Project Goals Improve stormwater quality reaching the Salinas River Reduce street flooding Recharge the groundwater table Replace aging utilities Improve safety and mobility for pedestrians and bicycles Shade the street with trees Promote infill and redevelopment

Case Study: 21 st St, Paso Robles

Andy Rowe, PE, LEED AP, QSD Cannon