Post-Construction RequirementsDesign Challenges

Dan Cloak, P.E.

Topics

• Low Impact Development Site Design– Design philosophy (what and why)– Benefits and some drawbacks

• Challenges to Achieving LID Site Design– Space constraints– Geotechnical and foundation design– Soil permeability– Groundwater

LID: What

• Preserve and replicate natural site hydrology

• Detain and retain runoff throughout the site

LID: Why?

• Why? Resilience.– Community engagement

and acceptance– Education and awareness– Habitat– Temperature moderation– Air quality– Most robust and effective treatment– Hydrologic control

LID: Challenges

• More facilities to build, maintain, and inspect

• Higher costs • More structural elements

(sidewalls, overflows)• More design effort

– Integration with buildings, parking, and circulation

Design Challenges and Solutions

• Space constraints– Integrate LID at earliest stages of design

• Geotechnical and foundation design– Modify and enhance structures

• Low permeability of soils• Groundwater

Space Constraints

• Solution: Incorporate site drainage and Stormwater Control Measures in preliminary site plan

Require Stormwater Plan Early

Pre-ApplicationMeeting

CompletedApplication

“DeemedComplete”

SectionReview

CEQAReview

Conditions ofApproval

Planning Commission

DetailedDesign

Plan Set and Permit

ApplicationConstruction

4% Sizing Factor (Tier 2)

½ Acre 4% 30 ft

Strategies to Minimize Facility Size

• Minimize impervious area• Make landscaped areas self-treating or

self-retaining• Disperse runoff to landscape

Example Commercial Site

Example Residential Subdivision

Non-LID Treatment

Steep Site, Remediated Slide

Next to Building Foundations

Bioretention & High Groundwater

6"

18"

Summary: LID Design Challenges

• Design for resilience• Disperse runoff where possible• Use the sizing calculator to iterate design• Get the geotech working with you