Urbanizing Watersheds: Green Infrastructure and Hydrologic Function Jay Dorsey, PE, PhD ODNR-DSWR October 30, 2014
Green Infrastructure Objectives Intentional about maintaining/replacing ecosystem functions and services Appropriate - fits site/setting Maintainable No unreasonable maintenance expectations Works with natural processes to sustain system functions Favorable long-term economics More than pays for itself over the long-term Minimizes off-site costs Increases livability during and resilience to extremes in climate/weather
Managing Watershed Hydrology Steering water (excess runoff volume) away from people, property, and infrastructure (e.g., roads, sanitary sewers) over the range of rainfall/runoff events for safety, appearance, and protection of property and infrastructure Releasing runoff to receiving waters in a way that supports stream stability/function, and maintains water quality and viable stream/lake ecosystems
Framework for Evaluating Green Infrastructure - Hydrology Streamflow characteristics Critical flows/flow duration/baseflow Runoff volume (V RO or RO) Volumetric runoff coefficient (CN, Rv, etc.) Sewershed or small watershed-scale hydrologic budget
Streamflow Criteria Critical discharge for stream bedload mobilization/stream stability Baseflow Flow duration
Flow Rate (cfs) Post-Urban Flows Pre-Urban Flows Qc Time
Cumulative Bed Load of Pre-dev. and No Control of Post-dev. (BDF=12) Bed Load (m 3 yr -1 ) 6 5 4 3 2 Trad BMPs GI Pre-development No Control Post-development 1 0 0.1 1 10 100 Recurrence Interval (yr) Source: Mecklenburg and Ward
Hydrologic Accounting P ET RO S F RO = P ds ET -F P Precipitation (Rainfall & Snowmelt) ET Evaporation & Transpiration S Temporary Storage F Infiltration (V INF ) RO Runoff (V RO ) All are volumes, though may be reported as a depth (vol/area)
Ohio Hydrologic Cycle
Ohio Hydrologic Cycle Immediate Fate of Rainfall S+E = 2 in = 6% P = 38 in = 100% RO = 10 in = 26% F = 26 in = 68%
Ohio Hydrologic Cycle Long-term Fate of Rainfall ET = 26 in = 68% P = 38 in = 100% RO = 10 in = 26% GW = 2 in = 5%
Long-term Rainfall Characteristics Dayton, OH Rain Events (1950-1999) 4000 3500 3000 2500 Count 2000 1500 1000 500 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.5 3.0 3.5 4.0 5.0 Rain Depth (in)
Long-term Rainfall Characteristics Burton OH Precipitation Events (1950-1990) 100.0 Cumulative Occurence Probability 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 0.00 0.50 1.00 1.50 2.00 2.50 3.00 Precipitation Depth (in)
WQv & Peak Discharge Events Burton OH Precipitation Events (1950-1990) 100.0 Cumulative Occurence Probability 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 0.00 0.50 WQv 1.00 1.50 1.35 2.00 2.1 2.50 3.00 0.75 Precipitation Depth (in) 1-yr, 24-hr
Sustainable Stormwater Mgmt Burton OH Precipitation Events (1950-1990) 100.0 Cumulative Occurence Probability 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 Retain Infiltrate or Re-use Capture & Manage for Water Quality and Channel Protection 0.00 0.50 WQv 1.00 1.50 2.00 2.1 2.50 3.00 0.75 Precipitation Depth (in) 1-yr, 24-hr Manage for Flood Control
Sustainable Stormwater Mgmt Burton OH Precipitation Events (1950-1990) 100.0 Cumulative Occurence Probability 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 Retain Infiltrate or Re-use What is an Appropriate Target Retention Volume? Capture & Manage for Water Quality and Channel Protection 0.00 0.50 WQv 1.00 1.50 2.00 2.1 2.50 3.00 0.75 Precipitation Depth (in) 1-yr, 24-hr Manage for Flood Control
Target Retention Volume? HSG-A HSG-B HSG-C HSG-D Woods CN 30 55 70 77 Ia 4.7 1.6 0.9 0.6 Pasture CN 39 61 74 80 Ia 3.1 1.3 0.7 0.5 Ag C & CR CN 64 74 81 85 Ia 1.1 0.7 0.5 0.4
HSG-C CN=74 Roofs, Pavement CN=98 HSG-D CN=80
Volume Reduction Potential P ET RO P Precipitation (Rainfall & Snowmelt) ET Evaporation & Transpiration S F S Temporary Storage F Infiltration (V INF ) RO Runoff (V RO ) RO = P ds ET - F
Volume Reduction Potential ET potential Infiltration capacity Surface or shallow infiltration Deeper percolation (incl. exfiltration from BMPs) provides groundwater recharge and interflow/baseflow to streams Temporary storage
Natural Stormwater Management
Landscape Components that Manage Stormwater Soil Flow paths Depressional storage Wetlands, etc. Floodplains Facilitated by plants and soil biota
Urban/Suburban Stormwater Management Systems From this: To this:
Landscape Components that Manage Stormwater Soil Flow paths Depressional storage Wetlands, etc. Floodplains Stormwater Practices and Green Infrastructure
Functional Urban Landscapes
Quick Note on Flow Paths It is hard to overstate the value of simply disconnecting impervious source areas (roofs, pavement) from the drainage network
HSG-C CN=74 Roofs, Pavement CN=98 HSG-D CN=80
Impervious Area Disconnection
Disconnection + Functional Flowpaths
Dublin Hospital
Volume Reduction Potential Green roofs Soils Bioretention (including rain gardens, tree planters and bioretention swales) Permeable pavement Dry detention basins Manufactured/proprietary systems
Evaporation Potential Source: ODNR
Green Roofs
Green Roof Volume Reduction From a review of green roof research literature, Berndtsson (2010) reported average volume reduction between 46 and 78% for five studies that measured rainfall/runoff for more than one year. ET = 15 25 in/yr
Green Roof Curve Number CN = 86 Source: Carter and Rasmussen (2006)
CN C = 74 CN D = 80 CN =??
CN =?? Probably>90 Built 1962
Soil Compaction
Stu Schwartz Photos
Stu Schwartz Graphic
Soil Renovation King County DES
Top Soil Specification Salem, Oregon Topsoil Standard
Functional Urban Soils Infiltration Capcity > 0.5 in/hr CN C = 74 CN D = 80 ET Potential 25-30 in/yr
Temporary Storage <<0.05 0.05-0.2 6 12 3 24
Rain Gardens Source: This Old House Source: NCSU Extension Source: C Francis Landscaping
Bioretention
Bioretention VaDCR
Internal Water Storage (IWS)
Holden Parking Lot Bioretention South A imp = 59% A brc /A imp = 5% North
Infiltration Tests Measured Kfs (in/hr) BRC1(N): 0.02, 0.02 BRC2(S): 0.02, 0.08
Holden North Cell Drawdown Data North Cell Well Drawdown Rates Drawdown Begin Date/Time Drawdown End Date/Time Beginning Stage (ft) Ending Stage (ft) Delta Stage (ft) Delta time (days) Drawdown Rate (ft/day) Drawdown Rate (in/hr) Infiltrated Volume (ft3) 10/7/2013 17:22 10/16/2013 0:30 2.099 1.17 0.929 8.30 0.112 0.056 261 10/17/2013 6:42 10/17/2013 15:38 2.085 1.97 0.115 0.37 0.309 0.154 32 10/18/2013 2:48 10/19/2013 12:20 2.084 1.721 0.363 1.40 0.260 0.130 102 10/20/2013 12:12 10/21/2013 20:30 2.052 1.624 0.428 1.35 0.318 0.159 120 10/22/2013 14:16 10/23/2013 7:02 2.07 1.783 0.287 0.70 0.411 0.205 81 10/26/2013 18:36 10/26/2013 21:12 1.923 1.894 0.029 0.11 0.268 0.134 8 10/27/2013 12:56 10/31/2013 4:00 1.892 1.352 0.54 3.63 0.149 0.074 151 11/2/2013 3:48 11/2/2013 9:22 1.883 1.815 0.068 0.23 0.293 0.147 19 11/4/2013 1:30 11/6/2013 17:18 1.847 1.344 0.503 2.66 0.189 0.095 141 11/9/2013 10:00 11/11/2013 17:46 1.851 1.355 0.496 2.32 0.213 0.107 139 11/15/2013 7:16 11/17/2013 18:46 1.794 1.491 0.303 2.48 0.122 0.061 85 11/19/2013 4:14 11/21/2013 21:28 1.789 1.279 0.51 2.72 0.188 0.094 143 11/23/2013 21:28 12/9/2013 9:06 1.811 1.165 0.646 15.48 0.042 0.021 181 Avg drawdown rate: 0.125 ft/day TotalExfiltrated Volume: 1463 Avg drawdown rate: 0.062 in/hr Standard Deviation: 0.0507 F north = 0.06 in/hr F south = 0.04 in/hr
Preliminary Curve Number for Holden Arboretum Outflow Volume (cubic feet) 6000 5000 4000 3000 2000 1000 0 N Cell No Treatment North Cell (cf) South Cell (cf) S Cell No Treatment 0 0.5 1 1.5 2 2.5 3 Rainfall Depth (in) RO T =0.25 Source: Ryan Winston, NCSU
Permeable Pavement NCState Photo UNHSC Photo
Perkins Twp Administration Permeable Pavement Aimp/Ainf = 3.1
Perkins Admin Infiltration Capacity Measured Kfs (in/hr) 0.01, 0.01, 0.04, 0.05 Measured Post-construction Drawdown Rate - 0.014 in/hr
Estimated Exfiltrated Volume Site Name Avg. DD Rate (in/hr) PP Surface Area (ft 2 ) Monitoring Period (days) Total Exfiltrate (ft 3 ) Exfiltrated Volume (ft 3 ) per day Perkins Township 0.014 2592 465 9031 19.5 Percentage of Rainfall Exfiltrated = 14%
Drainage vs. Rainfall Depth Outflow Vollume (ft 3 ) 4500 4000 3500 3000 2500 2000 1500 1000 500 0 RO T =0.3 y = 944.52x - 300 0 0.5 1 1.5 2 2.5 3 Rainfall Depth (in) Source: Ryan Winston, NCSU
Performance vs. Rainfall Depth Rainfall Depth (in) No. of Storms Reduction in Rainfall Volume (%) Minimum Mean Median Maximum 0-0.5 40 62 97 100 100 0.51-1.0 19 31 71 77 98 1.0+ 10 3 50 47 82 Source: Ryan Winston, NCSU
Curve Number at Perkins Admin Outflow Volume (ft 3 ) 4500 4000 3500 3000 2500 2000 1500 1000 500 0 No Controls CN = 94.5 Perm Pave CN = 82.5 0 0.5 1 1.5 2 2.5 3 Rainfall Depth (in) Source: Ryan Winston, NCSU
Underground Detention with Infiltration
Typical Ohio Dry Pond Infilt Capcity < 0.05 in/hr ET Potential Low
Dry Pond w/forebay & Micropool Micropool Forebay Infilt Capcity < 0.05 in/hr ET Potential Moderate
Can We Design More Functional Dry Basins? Infilt Capacity 0.1-1.0 in/hr ET Potential Very High
Estimated GI Hydrologic Impacts 50% impervious area, D soils Practice CN ET Potential (in/yr/dr.area) Vol Red % Soil Typical >90? <10 <40* Soil 4 good topsoil 85-90 15 40-50* Soil 8 good topsoil 80 25-30 60-80* Green Roof 4 media 85-90 15 40-50 Green Roof 8 media 80? 25 60-80 Bioretention @ 5% of A imp 18 IWS 85-90?? 40-50 Permeable Pavement w/6 sump 80?? 60-80 <2:1 A imp /A inf Permeable Pavement w/6 sump >3:1 A imp /A inf 85?? 40-50 * For turf area only
Summary Runoff volume is the most practical indicator of green infrastructure hydrologic function Functional urban landscapes depend on a combination of healthy soils, functional flow paths, and well-used storage Our current treatment of soils is a huge problem for managing watershed hydrology and is being misrepresented in our stormwater calculations Green infrastructure practices are able to help us attain watershed-scale hydrology equivalent to pasture or open space in good condition (e.g., CN D = 80) With a little forethought, dry basins can be a key component of our green infrastructure
Questions: Jay Dorsey Water Resources Engineer ODNR, Soil & Water Resources (614) 265-6647 jay.dorsey@dnr.state.oh.us