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

Clear Creek Solutions, Inc. This presentation was originally given at the ACEC LID Seminar in Sacramento, CA, in November 2008 by 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. Evaporate/transpire into the atmosphere. Runoff.

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)

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

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%)

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.

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.

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

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

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

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

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.

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)

Sample Stage-Storage-Discharge Table

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

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

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

HYDROLOGIC SIMULATION PROGRAM - FORTRAN 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

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

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

LID: Porous Pavement

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

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

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

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

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 1449 0.0% Porous 181 1268 87.5% 0.001 90 1359 93.8% 0.002 38 1411 97.4% 0.003 15 1434 99.0% 0.004 3 1446 99.8% 0.005 100.0%

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

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

Green roofs:

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

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

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

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

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

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

Bioretention/rain garden/landscape swale:

Bioretention: Planter Box

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

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

Northern California: Flow duration curves LID: Bioretention Northern California: Flow duration curves

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 1555 0.0% Bioretention 1523 32 2.1% 0.001 1437 118 7.6% 0.005 1334 221 14.2% 0.01 1244 311 20.0% 0.05 974 581 37.4% 0.1 833 722 46.4% 0.5 577 978 62.9% 1 468 1087 69.9% 5 399 1156 74.3% 10 50

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

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

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

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%

LID Hydrology and Hydraulic Modeling For more information Go to: www.clearcreeksolutions.com

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