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LID Hydrology and Hydraulics

LID Hydrology and Hydraulics. Doug Beyerlein, P.E. Clear Creek Solutions, Inc. www.clearcreeksolutions.com. LID Hydrology and Hydraulics Modeling. There is nothing magical about LIDs. Water must go somewhere. Water must either: Infiltrate into the soil.

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LID Hydrology and Hydraulics

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  1. LID Hydrology and Hydraulics Doug Beyerlein, P.E. Clear Creek Solutions, Inc. www.clearcreeksolutions.com

  2. LID Hydrology and Hydraulics Modeling There is nothing magical about LIDs. Water must go somewhere. Water must either: Infiltrate into the soil. Evaporate/transpire into the atmosphere. Runoff.

  3. Why LID Hydrology and Hydraulics Modeling? Effects of land use change on stormwater runoff: Less infiltration and evapotranspiration More surface runoff (increased volume) Runoff leaves the site faster (increased peak flows) Runoff occurs more often (increased duration) Runoff conveyed directly to creek (increased connectivity)

  4. Why Modeling? We use modeling to quantify the hydrologic impacts of LIDs in terms of: (1) Frequency (2) Duration (3) Volume

  5. Frequency Frequency is the probability of a certain size event occurring: 2-year (50% probability) 5-year (20%) 10-year (10%) 25-year (4%) 50-year (2%) 100-year (1%)

  6. Frequency Traditionally we have used single-event design storms to size facilities based on frequency. Design storm assumption: 25-year rainfall causes 25-year flood.

  7. Single-event design storm methodology doesn’t work for LID modeling because: • Single-event flow frequency standards are based on inappropriate assumptions. • Single-event modeling does not compute flow durations for hydromod requirements (flow duration is the percent of time flows exceed a specific value). • Single-event modeling does not include the long-term effects of evapotranspiration.

  8. Duration Flow Duration Analysis: Percent of time the flow exceeds a specific flow value.

  9. Durations • Hydromod flow duration standard: based on erosive flows. • Santa Clara, San Mateo, Alameda counties: 10% of 2-yr to 10-yr

  10. Durations • Hydromod flow duration standard: based on erosive flows. • San Diego County: 20% of 5-yr to 10-yr

  11. Volume Annual runoff volume reduction due to increased infiltration and evapotranspiration.

  12. Accurate simulation of LID hydrology requires continuous simulation modeling • Represent all of the components of the hydrologic cycle. • Include a full range of soil, vegetation, and topographic conditions. • Reproduce observed streamflow for both small and large drainages. • Use long-term local hourly precip to generate long-term hourly runoff.

  13. LID Hydraulics • Represents all conveyance systems, including LIDs. • Routes runoff using linear reservoir routing. • Represents conveyance systems with a table of stage-storage-discharge values (BAHM SSD Table or HSPF FTABLE). • Includes rainfall and evaporation on open water surfaces. • Includes infiltration (if turned on by user)

  14. Sample Stage-Storage-Discharge Table

  15. Potential LID Techniques/Facilities • stormwater infiltration ponds/basins • bioretention cells • planter boxes • porous pavement • green roofs • rain gardens • sand filters

  16. LID Hydrology and Hydraulics Modeling Results • porous pavement • green roofs • bioretention cells / planter boxes / rain gardens

  17. LID Modeling Options Based on continuous simulation hydrology: HSPF (WWHM, BAHM, SDHM) HEC-HMS SWMM

  18. HSPF: HYDROLOGIC SIMULATION PROGRAM - FORTRAN • Continuous simulation model • Natural and developed watersheds and water systems • Land surface and subsurface hydrology and quality processes • Stream/lake hydraulics and water quality processes • Time series data management and storage • Time series data statistical analysis and operations • Core watershed model in EPA BASINS and Army Corps WMS • Development and maintenance activities sponsored by U.S. EPA and U.S. Geological Survey

  19. HSPF: History • 1966 – Stanford Watershed Model by Linsley and Crawford • 1972 – HSP by Hydrocomp • 1973 – ARM (Agricultural Runoff Management) Model for EPA by Hydrocomp • 1974 – NPS (Non-Point Source) Model for EPA by Hydrocomp • 1979 – HSPF (combining HSP, ARM, and NPS) for EPA by Hydrocomp

  20. HSPF Made Easy: BAHM • BAHM: Bay Area Hydrology Model using San Jose rainfall data

  21. LID: Porous Pavement

  22. Porous Pavement Flow Paths Evaporation from pavement Rain on pavement Surface Runoff Infiltration through pavement Infiltration to gravel subgrade Underdrain Flow Infiltration to native soil

  23. LID: Porous Pavement • Modeling Assumptions: • Porous pavement thickness of 6 inches • Gravel subgrade thickness of 18 inches • Evaporation from gravel subgrade • Infiltration into native soil • No underdrain

  24. LID: Porous Pavement Northern California: Flow Frequency

  25. LID: Porous Pavement Northern California: Flow duration curves

  26. LID: Porous Pavement Northern California: Flow Duration Hours

  27. LID: Porous Pavement Northern California: Annual Flow Volume Reduction

  28. LID: Green Roof Green/vegetated/eco-roof Water is stored in the soil prior to runoff.

  29. Green roofs:

  30. LID: Green Roof • Modeling Assumptions: • Green roof vegetation is ground cover • Roof surface flat (< 1% slope) • Flow path length of 50 feet to a drain • No infiltration into building • No underdrain

  31. LID: Green Roof Northern California: Flow Frequency

  32. LID: Green Roof Northern California: Flow duration curves

  33. LID: Green Roof Northern California: Flow Duration Hours

  34. LID: Green Roof Northern California: Annual Flow Volume Reduction

  35. Rain Garden/Bioretention Rain garden/bioretention/landscape swale Water infiltrates into the soil before runoff.

  36. Bioretention/rain garden/landscape swale:

  37. Bioretention: Planter Box

  38. LID: Bioretention • Modeling Assumptions: • Drainage area is 1 acre of impervious surface • Bioretention area is 5% of impervious area draining to it • Top layer of bioretention area is amended soil • Amended soil thickness of 24 inches • Amended soil infiltration rate equals 2 inches per hour • No underdrain

  39. LID: Bioretention Northern California: Flow Frequency

  40. LID: Bioretention Northern California: Flow duration curves

  41. LID: Bioretention Northern California: Flow Duration Hours

  42. LID: Bioretention Northern California: Annual Flow Volume Reduction

  43. Summary • Porous pavement can provide 100% reduction in runoff volume, peak flows (frequency), and durations at very low infiltration rates (< 0.01 in/hr).

  44. Summary • Green roofs reduce • runoff volume by 40-70% • runoff durations by 70-90% • peak flows by 40-50%

  45. Summary • Bioretention reduces • volume and durations by 10-20% for poor draining soils • volume and durations by 50-70% for well drained soils • peak flows by 5-20%

  46. LID Hydrology and Hydraulic Modeling • For more informationGo to:www.clearcreeksolutions.com

  47. LID Modeling • Questions?Contact:Doug Beyerlein 425.892.6454beyerlein@clearcreeksolutions.com

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