module 2: bioretention area siting and design andy rowe, pe, leed ap, qsd cannon

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 – 21st 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 GameSource: 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: 21st St, Paso Robles

Source: City of Paso Robles

Case Study: 21st St, Paso Robles

Case Study: 21st St, Paso Robles

Case Study: 21st 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: 21st St, Paso Robles

Case Study: 21st St, Paso Robles

Case Study: 21st St, Paso Robles

Case Study: 21st St, Paso Robles

Case Study: 21st St, Paso Robles

Case Study: 21st St, Paso Robles

Case Study: 21st St, Paso Robles

Case Study: 21st St, Paso Robles

Case Study: 21st St, Paso Robles

Case Study: 21st St, Paso Robles

Andy Rowe, PE, LEED AP, QSD

Cannon

andyr@cannoncorp.us