INLAND EMPIRE ASCE & APWA LOW IMPACT DEVELOPMENT (LID) SEMINAR INLAND EMPIRE ASCE & APWA LOW IMPACT DEVELOPMENT (LID) SEMINAR LID FACILITY DESIGN Prepared by Eric Prepared by Eric Mosolgo October 14, 2009 Riverside, California

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

Background San Diego HMP and Model SUSMP Update Sacramento HMP

Background Watershed and Stream Scale Site scale Reduce peak flows Detain runoff on site Increase time of concentration Slow runoff from leaving site No runoff from small storms Infiltrate and evapotranspirate Reduce duration of moderate flows Let runoff seep away very slowly Reduce runoff volume Infiltrate where possible Reduce runoff energy Detain and slow flows Increase groundwater storage and stream base flows Facilitate infiltration Reduce pollutants in runoff Detain and filter runoff Protect against spills and dumping Disconnect drainage and filter runoff

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

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

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

Presentation Overview Maintenance and Monitoring Requirements

Design Considerations Urban Retrofit Challenges Bioretention basins Rain gardens Bioretention swales Bioretention in combination with vaults Flow-through planter boxes Porous pavement Rainwater collection systems

Design Considerations Urban Retrofit Challenges Lateral migration of infiltrated runoff Downstream ponding problems Infiltrated runoff to joint trench LID options for roadway design

Design Considerations Urban 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

Design Considerations Arid 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

Design Considerations LID 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

Design Considerations LID Hydromodification Mitigation

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)

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

Summary of Existing LID Software Contra 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

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

Summary of LID Modeling Software San 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

Summary of Existing LID Modeling Software Treatment & Flow Control NRCS Soil Group ABCD Bioretention Facility A V1V1V1V V2V2V2V2N/AN/A Flow-through Planter AN/AN/A V1V1V1V1N/AN/A V2V2V2V2N/AN/A Dry Well A N/AN/A V N/AN/A Cistern + bioretention facility A (bioretention facility) V (cistern)

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

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)

Hydrologic and Hydraulic Analysis Input Summary

Hydrologic and Hydraulic Analysis Output Summary

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

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

Questions? Eric Mosolgo, PE Brown and Caldwell (858)