Northern%20California%20LID%20Hydrology%20and%20Hydraulics

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Northern CaliforniaLID Hydrology and Hydraulics

• Doug Beyerlein, P.E.
• Clear Creek Solutions, Inc.
• www.clearcreeksolutions.com

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This presentation was originally given at the
ACEC LID Seminar in Sacramento, CA, in November
2008by

• Doug Beyerlein, P.E.
• Clear Creek Solutions, Inc.
• www.clearcreeksolutions.com

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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.

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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)

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Why Modeling?

• We use modeling to quantify the hydrologic
  impacts of LIDs in terms of
• (1) Frequency
• (2) Duration
• (3) Volume

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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)

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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.

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• 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.

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

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

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Durations

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

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Volume

• Annual runoff volume reduction due to increased
  infiltration and evapotranspiration.

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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.

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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)

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Sample Stage-Storage-Discharge Table
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Potential LID Techniques/Facilities

• stormwater infiltration ponds/basins
• bioretention cells
• planter boxes
• porous pavement
• green roofs
• rain gardens
• sand filters

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LID Hydrology and Hydraulics Modeling Results

• porous pavement
• green roofs
• bioretention cells / planter boxes / rain
  gardens

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LID Modeling Options

• Based on continuous simulation hydrology
• HSPF (WWHM, BAHM, SDHM)
• HEC-HMS
• SWMM

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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

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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

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HSPF Made Easy BAHM

• BAHM Bay Area Hydrology Model using San Jose
  rainfall data

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LID Porous Pavement

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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
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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

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LID Porous Pavement
Northern California Flow Frequency
Site Native Soil Infiltration (in/hr) 10-Yr Flow (cfs/ac) Reduction (cfs/ac) Reduction ()
Impervious 0 0.603 0.000 0.0
Porous 0 0.330 0.273 45.3
Porous 0.001 0.216 0.387 64.2
Porous 0.002 0.155 0.448 74.3
Porous 0.003 0.057 0.546 90.5
Porous 0.004 0.000 0.603 100.0
Porous 0.005 0.000 0.603 100.0

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LID Porous Pavement

Northern California Flow duration curves
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LID Porous Pavement
Northern California Flow Duration Hours
Site Native Soil Infiltration (in/hr) Flow Duration hours (0.1 cfs/ac) Reduction (cfs/ac) Reduction ()
Impervious 0 1449 0 0.0
Porous 0 181 1268 87.5
Porous 0.001 90 1359 93.8
Porous 0.002 38 1411 97.4
Porous 0.003 15 1434 99.0
Porous 0.004 3 1446 99.8
Porous 0.005 0 1449 100.0

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LID Porous Pavement
Northern California Annual Flow Volume Reduction
Site Native Soil Infiltration (in/hr) Total Runoff (in/yr) Reduction (in/yr) Reduction ()
Impervious 0 12.371 0.000 0.0
Porous 0 1.882 10.489 84.8
Porous 0.001 0.953 11.418 92.3
Porous 0.002 0.414 11.957 96.7
Porous 0.003 0.112 12.259 99.1
Porous 0.004 0.030 12.341 99.8
Porous 0.005 0.000 12.371 100.0

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LID Green Roof
Green/vegetated/eco-roof

Water is stored in the soil prior to runoff.
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Green roofs

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LID Green Roof

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

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LID Green Roof
Northern California Flow Frequency
Site Soil Depth (in) 10-Yr Flow (cfs/ac) Reduction (cfs/ac) Reduction ()
Impervious 0 0.603 0.000 0.0
Green 2 0.372 0.231 38.3
Green 3 0.358 0.245 40.6
Green 4 0.351 0.252 41.8
Green 5 0.346 0.257 42.6
Green 6 0.343 0.260 43.1
Green 7 0.340 0.263 43.6
Green 8 0.338 0.265 43.9
Green 9 0.335 0.268 44.4
Green 10 0.332 0.271 44.9
Green 11 0.327 0.276 45.8
Green 12 0.323 0.280 46.4

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LID Green Roof
Northern California Flow duration curves
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LID Green Roof
Northern California Flow Duration Hours
Site Soil Depth (in) Flow Duration hours (0.1 cfs/ac) Reduction (cfs/ac) Reduction ()
Impervious 0 1449 0 0.0
Green 2 336 1113 76.8
Green 3 305 1144 79.0
Green 4 277 1172 80.9
Green 5 251 1198 82.7
Green 6 231 1218 84.1
Green 7 211 1238 85.4
Green 8 182 1267 87.4
Green 9 169 1280 88.3
Green 10 156 1293 89.2
Green 11 148 1301 89.8
Green 12 137 1312 90.5

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LID Green Roof
Northern California Annual Flow Volume Reduction
Site Soil Depth (in) Total Runoff (in/yr) Reduction (in/yr) Reduction ()
Impervious 0 12.371 0.000 0.0
Green 2 7.173 5.198 42.0
Green 3 6.607 5.764 46.6
Green 4 6.175 6.196 50.1
Green 5 5.812 6.559 53.0
Green 6 5.486 6.885 55.7
Green 7 5.185 7.187 58.1
Green 8 4.904 7.467 60.4
Green 9 4.642 7.729 62.5
Green 10 4.397 7.974 64.5
Green 11 4.168 8.203 66.3
Green 12 3.953 8.418 68.0

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Rain Garden/Bioretention
Rain garden/bioretention/landscape swale

Water infiltrates into the soil before runoff.
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Bioretention/rain garden/landscape swale

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Bioretention Planter Box

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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

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LID Bioretention
Northern California Flow Frequency
Site Native Soil Infiltration (in/hr) 10-Yr Flow (cfs/ac) Reduction (cfs/ac) Reduction ()
Impervious 0 0.633 0.000 0.0
Bioretention 0 0.598 0.035 5.5
Bioretention 0.001 0.598 0.035 5.5
Bioretention 0.005 0.594 0.039 6.2
Bioretention 0.01 0.594 0.039 6.2
Bioretention 0.05 0.542 0.091 14.4
Bioretention 0.1 0.535 0.098 15.5
Bioretention 0.5 0.516 0.117 18.5
Bioretention 1 0.488 0.145 22.9
Bioretention 5 0.485 0.148 23.4
Bioretention 10 0.485 0.148 23.4
Bioretention 50 0.485 0.148 23.4

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LID Bioretention

Northern California Flow duration curves
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LID Bioretention
Northern California Flow Duration Hours
Site Native Soil Infiltration (in/hr) Flow Duration hours (0.1 cfs/ac) Reduction (cfs/ac) Reduction ()
Impervious 0 1555 0 0.0
Bioretention 0 1523 32 2.1
Bioretention 0.001 1437 118 7.6
Bioretention 0.005 1334 221 14.2
Bioretention 0.01 1244 311 20.0
Bioretention 0.05 974 581 37.4
Bioretention 0.1 833 722 46.4
Bioretention 0.5 577 978 62.9
Bioretention 1 468 1087 69.9
Bioretention 5 399 1156 74.3
Bioretention 10 399 1156 74.3
Bioretention 50 399 1156 74.3

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LID Bioretention
Northern California Annual Flow Volume Reduction
Site Native Soil Infiltration (in/hr) Total Runoff (in/yr) Reduction (in/yr) Reduction ()
Impervious 0 12.990 0.000 0.0
Bioretention 0 12.900 0.090 0.7
Bioretention 0.001 11.882 1.108 8.5
Bioretention 0.005 11.096 1.893 14.6
Bioretention 0.01 10.327 2.663 20.5
Bioretention 0.05 7.733 5.257 40.5
Bioretention 0.1 6.519 6.471 49.8
Bioretention 0.5 4.367 8.622 66.4
Bioretention 1 3.594 9.396 72.3
Bioretention 5 3.063 9.927 76.4
Bioretention 10 3.063 9.927 76.4
Bioretention 50 3.063 9.927 76.4

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Summary

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

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Summary

• Green roofs reduce
• runoff volume by 40-70
• runoff durations by 70-90
• peak flows by 40-50

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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

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LID Hydrology and Hydraulic Modeling

• For more informationGo to www.clearcreeksolut
  ions.com

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LID Modeling

• Questions?Contact Doug Beyerlein
  425.892.6454beyerlein_at_clearcreeksolutions.com