INLAND EMPIRE ASCE & APWA LOW IMPACT DEVELOPMENT (LID) SEMINAR LID FACILITY DESIGN

1. INLAND EMPIRE ASCE & APWALOW IMPACT DEVELOPMENT (LID) SEMINARLID FACILITY DESIGN Prepared by Eric Mosolgo October 14, 2009 Riverside, California

2. Background • Contra Costa Approach • Stormwater treatment and flow control • Minimize directly connected impervious areas • Avoid standing water / vector issues

3. Background • San Diego HMP and Model SUSMP Update • Sacramento HMP

4. Background

5. Presentation Overview • Design Considerations • Urban Retrofit Challenges • Arid Climate Design Adjustments • Hydromodification Mitigation with LID

6. Presentation Overview • Modeling Approaches and Summary of Existing Software • Single-Event Modeling • Continuous Simulation Modeling

7. Presentation Overview • Hydrologic and Hydraulic Analysis • Single Event Model Example • Continuous Simulation Model Example

8. Presentation Overview • Maintenance and Monitoring Requirements

9. Design ConsiderationsUrban Retrofit Challenges • Bioretention basins • Rain gardens • Bioretention swales • Bioretention in combination with vaults • Flow-through planter boxes • Porous pavement • Rainwater collection systems

10. Design ConsiderationsUrban Retrofit Challenges • Lateral migration of infiltrated runoff • Downstream ponding problems • Infiltrated runoff to joint trench • LID options for roadway design

11. Design ConsiderationsUrban Retrofit Challenges • WQ Storage in voids of sub-surface soil layer • Amended soils; minimize soil compaction • Soil infiltration rate should exceed 1.5 in/hr • 50% sand, 25% compost, 25% planting soil • 30% voids • Soil depth of 4 feet recommended for bioretention areas with trees

12. Design ConsiderationsArid Climate Adjustments • Native and drought-tolerant plants • Varying pollutant loading and ponding levels • Conflict with water conservation goals • BMPs used in arid environments will require monitoring to assess performance • Rainfall analysis methods

13. Design ConsiderationsLID Hydromodification Mitigation • Rainfall adjustments • Locate LID in areas of pervious (A or B) soils • Surface reservoir must fill • Drawdown time requirement • Offsite area restrictions • Varying lower flow thresholds • Minimum orifice size criteria

14. Design ConsiderationsLID Hydromodification Mitigation

15. Design ConsiderationsLID Hydromodification Mitigation

16. LID Modeling Approaches • General sizing approach for bioretention basins, bioretention swales and rain gardens • Limit contributing watershed area (dispersed facilities) • Fast-draining soils (amended soils)

17. Summary of Existing LID Modeling Software • Single-Event Models • Continuous Simulation Models • HSPF • HEC-HMS • SWMM • Contra Costa LID Sizing Calculator • San Diego HMP / LID Sizing Calculator

18. Summary of Existing LID SoftwareContra Costa Sizing Calculator • Sizing Factor Development • Soil Group • Land Use • Treatment / Mitigation Approach • Soil Physics at BMP Layer Interfaces • WQ only sizing factors • WQ + Flow Control Sizing Factors

19. Summary of LID Modeling Software San Diego HMP / LID Calculator • Detention Basin Calculator (low flow orifice and overflow weir) • Pond configuration and outlet structure criteria • LID credit to reduce pond sizing • Graphical Output of Peak Flow Frequency and Flow Duration Response • Automated Rainfall Gage Selection

20. Summary of LID Modeling SoftwareSan Diego HMP / LID Calculator • Infiltration Devices for Parking Lots (scaling factor that varies with depth / bottom area ratio) • Infiltration strips and tree wells • Treatment only option for vegetated swales • Extended detention basin option • Incorporation of generic LID options for BMP manufacturers • Pervious pavement

21. Summary of ExistingLID Modeling Software

22. Hydrologic and Hydraulic Analysis • Single-Event Example 0.2 inches/hour BMP Area/Impervious Area = 0.2/5 = 0.04 Planting medium i = 5 inches/hour

23. Hydrologic and Hydraulic Analysis • Continuous simulation model example • Match pre-project flows and durations in the geomorphically significant flow range • Peak flow frequency statistics based on partial duration calculations • Parameter estimation (infiltration, evaporation)

24. Hydrologic and Hydraulic AnalysisInput Summary

25. Hydrologic and Hydraulic AnalysisOutput Summary

26. Maintenance Requirements • HOA maintenance • Regular inspections to verify vegetative establishment and prevent invasive vegetation • Removal of accumulated sediment • Replacement of dead vegetation, erosion repair at inflow, unclogging the underdrain • Checks for standing water • Vector control

27. Monitoring Requirements • Collect data for minimum of 2 rainy seasons • Monitoring sites should cover range of development types, have applicable rain gage data, be located in headwaters of watersheds, be located upstream of variety of receiving channel types. • Obtain facility inflows and outflows • Compare collected data to predicted data

28. Questions? Eric Mosolgo, PE Brown and Caldwell (858) 571-6736 emosolgo@brwncald.com