Clear Creek Solutions, Inc. LID Hydrology and Hydraulics Doug Beyerlein, P.E. Clear Creek Solutions, Inc. Clear Creek Solutions, Inc. LID Hydrology and Hydraulics Modeling There is nothing magical about LIDs. Water must go somewhere. Water must either: 1. 1.Infiltrate into the soil Evaporate/transpire into the atmosphere Runoff. Clear Creek Solutions, Inc. 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) Clear Creek Solutions, Inc. Why Modeling? We use modeling to quantify the hydrologic impacts of LIDs in terms of: (1) Frequency (2) Duration (3) Volume Clear Creek Solutions, Inc. 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%) Clear Creek Solutions, Inc. 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. Clear Creek Solutions, Inc. Single-event design storm methodology doesnt 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. Clear Creek Solutions, Inc. Duration Flow Duration Analysis: Percent of time the flow exceeds a specific flow value. Clear Creek Solutions, Inc. Durations Hydromod flow duration standard: based on erosive flows. Santa Clara, San Mateo, Alameda counties: 10% of 2-yr to 10-yr Clear Creek Solutions, Inc. Durations Hydromod flow duration standard: based on erosive flows. San Diego County: 20% of 5-yr to 10-yr Clear Creek Solutions, Inc. Volume Annual runoff volume reduction due to increased infiltration and evapotranspiration. Clear Creek Solutions, Inc. 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. Clear Creek Solutions, Inc. 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) Clear Creek Solutions, Inc. Sample Stage-Storage-Discharge Table Clear Creek Solutions, Inc. Potential LID Techniques/Facilities stormwater infiltration ponds/basins bioretention cells planter boxes porous pavement green roofs rain gardens sand filters Clear Creek Solutions, Inc. LID Hydrology and Hydraulics Modeling Results porous pavement green roofs bioretention cells / planter boxes / rain gardens Clear Creek Solutions, Inc. LID Modeling Options Based on continuous simulation hydrology: HSPF (WWHM, BAHM, SDHM) HEC-HMS SWMM Clear Creek Solutions, Inc. 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 Clear Creek Solutions, Inc. 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 Clear Creek Solutions, Inc. HSPF Made Easy: SDHM SDHM: San Diego Hydrology Model using San Diego (Lindbergh Field) rainfall data Clear Creek Solutions, Inc. LID: Porous Pavement Clear Creek Solutions, Inc. Porous Pavement Flow Paths Infiltration to native soil Surface Runoff Rain on pavement Infiltration to gravel subgrade Underdrain Flow Infiltration through pavement Evaporation from pavement Clear Creek Solutions, Inc. 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 Clear Creek Solutions, Inc. LID: Porous Pavement Southern California: Flow Frequency Site Native Soil Infiltration (in/hr) 10-Yr Flow (cfs/ac) Reduction (cfs/ac) Reduction (%) Impervious % Porous % Porous % Porous % Clear Creek Solutions, Inc. LID: Porous Pavement Southern California: Flow duration curves Clear Creek Solutions, Inc. LID: Porous Pavement Southern California: Flow Duration Hours Site Native Soil Infiltration (in/hr) Flow Duration hours (0.1 cfs/ac) Reduction (cfs/ac) Reduction (%) Impervious % Porous % Porous % Porous % Porous % Clear Creek Solutions, Inc. LID: Porous Pavement Southern California: Annual Flow Volume Reduction Site Native Soil Infiltration (in/hr) Total Runoff (in/yr) Reduction (in/yr) Reduction (%) Impervious % Porous % Porous % Porous % Porous % Porous % Clear Creek Solutions, Inc. LID: Green Roof Green/vegetated/eco-roof Water is stored in the soil prior to runoff. Clear Creek Solutions, Inc. Green roofs: Clear Creek Solutions, Inc. 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 Clear Creek Solutions, Inc. LID: Green Roof Southern California: Flow Frequency Site Soil Depth (in) 10-Yr Flow (cfs/ac) Reduction (cfs/ac) Reduction (%) Impervious % Green % Green % Green % Green % Green % Green % Green % Green % Green % Green % Green % Clear Creek Solutions, Inc. LID: Green Roof Southern California: Flow duration curves Clear Creek Solutions, Inc. LID: Green Roof Southern California: Flow Duration Hours Site Soil Depth (in) Flow Duration hours (0.1 cfs/ac) Reduction (cfs/ac) Reduction (%) Impervious % Green % Green % Green % Green % Green % Green % Green % Green % Green % Green % Green % Clear Creek Solutions, Inc. LID: Green Roof Southern California: Annual Flow Volume Reduction Site Soil Depth (in) Total Runoff (in/yr) Reduction (in/yr) Reduction (%) Impervious % Green % Green % Green % Green % Green % Green % Green % Green % Green % Green % Green % Clear Creek Solutions, Inc. Rain Garden/Bioretention Rain garden/bioretention/landscape swale Water infiltrates into the soil before runoff. Clear Creek Solutions, Inc. Bioretention/rain garden/landscape swale: Clear Creek Solutions, Inc. Bioretention: Planter Box Clear Creek Solutions, Inc. 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 Clear Creek Solutions, Inc. LID: Bioretention Southern California: Flow Frequency Site Native Soil Infiltration (in/hr) 10-Yr Flow (cfs/ac) Reduction (cfs/ac) Reduction (%) Impervious % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Clear Creek Solutions, Inc. LID: Bioretention Southern California: Flow duration curves Clear Creek Solutions, Inc. LID: Bioretention Southern California: Flow Duration Hours Site Native Soil Infiltration (in/hr) Flow Duration hours (0.1 cfs/ac) Reduction (cfs/ac) Reduction (%) Impervious % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Clear Creek Solutions, Inc. LID: Bioretention Southern California: Annual Flow Volume Reduction Site Native Soil Infiltration (in/hr) Total Runoff (in/yr) Reduction (in/yr) Reduction (%) Impervious % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Bioretention % Clear Creek Solutions, Inc. Summary Porous pavement can provide 100% reduction in runoff volume, peak flows (frequency), and durations at very low infiltration rates (< 0.01 in/hr). Clear Creek Solutions, Inc. Summary Green roofs reduce runoff volume by 50-80% runoff durations by 80-95% peak flows by 50-70% Clear Creek Solutions, Inc. Summary Bioretention reduces volume and durations by 10-30% for poor draining soils volume and durations by 40-70% for well drained soils peak flows by 10-25% Clear Creek Solutions, Inc. LID Hydrology and Hydraulic Modeling For more information Go to: Clear Creek Solutions, Inc. LID Modeling Questions? Contact: Doug Beyerlein