Sustainable Site Development and Conservation Design Considerations for Stormwater Control

Transcription

1 Sustainable Site Development and Conservation Design Considerations for Stormwater Control Robert Pitt, P.E., Ph.D., BCEE, D.WRE Department of Civil, Construction, and Environmental Engineering The University of Alabama Photo by Lovena, Harrisburg, PA Conservation Design Approach for New Development Better site planning to maximize soil and water resources and topography of site Emphasize water conservation and beneficial uses of stormwater on site Encourage infiltration of runoff at site Treat water at critical source areas Treat runoff that cannot be infiltrated at site 1

2 Roof Runoff Control Options Downspout disconnections Rain gardens Green roofs Beneficial use of roof runoff One of the simplest and most effective approaches for the control of stormwater is to reduce the amount of impervious areas that are directly connected to the drainage system. This can be accomplished by using less paved and roof areas (hard to do and meet design objectives), disconnect the impervious areas, or reduce the runoff from the impervious areas by infiltration, or other, methods. Reducing the runoff volume also reduces the pollutant discharges, reduces peak flows, and reduces combined sewer overflows. Disconnected roof drain Directly connected roof drain 2

3 Roof drain disconnections. Burnsville, Minnesota, Rainwater Gardens 97% Runoff Volume Reduction An example of the dramatic runoff volume reductions possible through the use of conservation design principles (17 rain gardens, at about $3,000 each, at 14 homes in one neighborhood) Land and Water, Sept/Oct

4 Rain Garden Designed for Complete Infiltration of Roof Runoff Green roof, Portland, OR 4

5 Green Roofing Extensive Green Roof Lighter <6 media depth Planted with sedums or native plant species Saturated weights from 12-50lbs/sq.ft. Intensive Green Roof Heavier >12 media depth Wider variety of plants which need more care and irrigation Saturated weights from lbs/sq.ft. Urban Heat Island Effect Atlanta, GA Can a green roof make an urban area look like a suburban area? Urban Temp. - Day Suburban Temp. - Day Urban Temp. - Night Suburban Temp. - Night Images Courtesy of NASA 5

6 Evapotranspiration (ET) is the major rain abstraction mechanism available for green roofs, besides some detention storage and evaporation. Plant Cool Season Grass (turfgrass) Crop Coefficient Factor (Kc) Root Depth (ft) Common Trees Annuals Common Shrubs Warm Season Grass Prairie Plants (deep rooted) Central Alabama January February March April May June July August September October November December Average daily ET o reference conditions (inches/day) (irrigated alfalfa) Recent results showing green roof runoff benefits compared to conventional roofing (data from Shirley Clark, Penn State Harrisburg) Greater than 65% volume reductions due to ET 6

7 Beneficial use of stormwater as a local resource needs to be seriously considered Prince George s County phot Calculated Benefits of Various Roof Runoff Controls (compared to typical directly connected residential pitched roofs) Annual roof runoff volume reductions Birmingham, Alabama (55.5 in. annual rain) Seattle, Wash. (33.4 in.) Phoenix, Arizona (9.6 in.) Flat roofs instead of pitched roofs 13% 21% 25% Cistern for reuse of runoff for toilet flushing and irrigation (10 ft. diameter x 5 ft. high) Planted green roof (but will need to irrigate during dry periods) Disconnect roof drains to loam soils Rain garden with amended soils (10 ft. x 6.5 ft.)

8 Pavement Runoff Control Options Bioretention Biofiltration (with underdrains) Porous Pavement Infiltration/Biofiltration Infiltration trenches Infiltrating swales Infiltration ponds Porous pavement Percolation ponds Biofiltration areas (rain gardens, etc.) 8

9 Small depressions graded near parking lots or buildings for infiltration (older method, using regular turf grass) (MD and WI). Portland, Oregon, bioretention areas to capture and treat parking lot runoff. 9

10 Parking lot medians easily modified for bioretention (OR and MD). Larry Coffman Larry Coffman Recent Bioretention Retrofit Projects in Commercial and Residential Areas in Madison, Wisconsin 10

11 Neenah Foundry Employee Parking Lot Grass Filter/Biofilter, Neenah, Wisconsin Bioretention and biofiltration areas having moderate capacity Surface overflow Portland, Oregon 11

12 Stormwater filters and bioretention areas in ultra urban setting (Melbourne, Australia) Street-side tree biofilters in downtown area (Melbourne, Australia) 12

13 Porous paver blocks have been used in many locations to reduce runoff to combined sewer systems, thereby reducing overflow frequency and volumes (Sweden, Germany, and WI). Not recommended in areas of heavy automobile use due to groundwater contamination (provide little capture of critical pollutants, plus most manufactures recommend use of heavy salt applications instead of sand for ice control). Essen, Germany Austin, TX Singapore Zurich Davos, Switzerland Singapore 13

14 Temporary parking or access roads supported by turf meshes, or paver blocks, and advanced porous paver systems designed for large capacity. Soil modifications for rain gardens and other biofiltration areas can significantly increase treatment and infiltration capacity compared to native soils. (King County, Washington, test plots) 14

15 Grass Filtering of Stormwater Sediment Particulate Removal in Shallow Flowing Grass Swales and in Grass Filters Runoff from Pervious/ impervious area Reducing velocity of runoff Trapping of sediments and associated pollutants Sediment particles Infiltration Reduced volume and treated runoff 15

16 Date: 10/11/ ft 75 ft TSS: 10 mg/l TSS: 20 mg/l 25 ft TSS: 30 mg/l 6 ft 3 ft 2 ft TSS: 63 mg/l TSS: 35 mg/l Head (0ft) TSS: 84 mg/l TSS: 102 mg/l Large capacity grass swales and channels designed for both conveyance and water quality objectives. 16

17 Grass Swales Designed to Infiltrate Large Fractions of Runoff (Alabama). Also incorporate grass filtering before infiltration Swales can be both interesting and fit site development objectives. Tuscaloosa, AL Street Edge Alternative (SEA St) Seattle, WA 17

18 Conventional curbs with inlets directed to site swales WI WI DNR photo MS Treatment of Flows in Excess of Infiltration Capacity Wet detention ponds, stormwater filters, or correctly-sized critical source area controls needed to treat runoff that cannot be infiltrated. 18

19 Wet Detention Ponds Suspended Solids Control at Monroe St. Detention Pond, Madison, WI (USGS and WI DNR data) Consistently high TSS removals for all influent concentrations (but better at higher concentrations, as expected) 19

20 Wet detention ponds The regional swales will direct excess water into the ponds. Typical pond section: The pond surface areas vary from 0.5 to 1% of the drainage areas, depending on the amount of upland infiltration. The ponds have 3 ft. of standing water above 2 ft. of sacrificial storage. The live storage volume provides necessary peak flow control. Treatment of Runoff from Critical Source Areas Flow diversion Treatment trains having combinations of effective unit processes targeted to pollutants of interest Pollution prevention through the use of noncontaminating exposed materials 20

21 Critical Source Area Control Covering fueling area Berm around storage tanks correctly-sized critical source area controls needed to treat runoff originating from heavily contaminated areas Austin sand filter MCTT 21

22 Multi-Chambered Treatment Train (MCTT) for stormwater control at large critical source areas Milwaukee, WI, Ruby Garage Maintenance Yard MCTT Installation Pilot-Scale MCTT Test Results influent effluent Ruby Garage MCTT samples 22

23 Upflow Filter TM Upflow filter insert for catchbasins Able to remove particulates and targeted pollutants at small critical source areas. Also traps coarse material and floatables in sump and away from flow path. Performance Plot for Mixed Media on Suspended Soilds for Influent Concentrations of 500 mg/l, 250mg/L, 100 mg/l and 50 mg/l 600 High Flow 500 Flow (gpm) Pelletized Peat, Activated Carbon, and Fine 300 Sand y = x R 2 = Suspended Soilds (mg/l) Influent Conc. Effluent Conc. Mid Flow 500 Low Flow 500 High Flow 250 Mid Flow 250 Low Flow 250 High Flow 100 Mid Flow 100 Low Flow 100 High Flow 50 Mid Flow 50 Low Flow Headloss (inches) High Zinc Concentrations have been Found in Roof Runoff for Many Years at Many Locations Typical Zn in stormwater is about 100 g/l, with industrial area runoff usually several times this level. Water quality criteria for Zn is as low as 100 g/l for aquatic life protection in soft waters, up to about 5 mg/l for drinking waters. Zinc in runoff from galvanized roofs can be several mg/l Other pollutants and other materials also of potential concern. A cost-effective stormwater control strategy should include the use of materials that have reduced effects on runoff degradation. 23

24 2005: Testing Frame Set-Ups at Penn State-Harrisburg and the University of Alabama at Birmingham Six frames and 12 panels being tested at each site Examples Utilizing these Concepts Retrofitted bioretention and wet ponds at big box commercial development in VT Beneficial use of stormwater at university in AL Multi-faceted conservation design at residential development in WI Multi-faceted conservation design at industrial site in AL Large rain garden at transportation corridor in WI Green infrastructure retrofitted in combined sewer area in MO Groundwater effects with dry wells in NJ 24

25 Big box development stormwater management options. Summary of Measured Areas Totally connected impervious areas: 25.9 acres parking 15.3 acres roofs (flat) 8.2 acres streets (1.2 curb-miles and 33 ft wide) 2.4 acres Landscaped/open space 15.4 acres Total Area 41.3 acres 25

26 Stormwater Controls Biofiltration areas (parking lot islands) 52 units of 40 ft by 8 ft Surface area: 320 ft 2 Bottom area: 300 ft 2 Depth: 1 ft Vertical stand pipe: 0.5 ft. dia ft high Broad-crested weir overflow: 8 ft long, 0.25 ft wide and 0.9 ft high Amended soil: sandy loam Also examined wet detention ponds Runoff Volume Changes Runoff volume (10 6 ft 3 /yr) Base conditions With biofiltration Average Rv % reduction in volume n/a 41% 26

27 Birmingham Southern College Campus (map by Jefferson County Stormwater Management Authority) Birmingham Southern College Fraternity Row Acres % of Total Roadways % Parking Walks Roofs Landscaping Total:

28 Supplemental Irrigation Late Fall and Winter (Nov-March) Inches per month (example) Average Use for 1/2 acre (gal/day) 1 to 1-1/ Spring (April-May) 2 to Summer (June- August) Fall (Sept-Oct) 2 to Total: 28 (added to 54 inches of rain) Capture and Reuse of Roof Runoff for Supplemental Irrigation Tankage Volume (ft 3 ) per 4,000 ft 2 Building Percentage of Annual Roof Runoff used for Irrigation 1,000 56% 2, , , ,

29 Combinations of Controls to Reduce Runoff Volume Total Annual Runoff (ft 3 /year) Undeveloped 46, Conventional development 380, X Grass swales and walkway porous 260, pavers Grass swales and walkway porous 170, pavers, plus roof runoff disconnections Grass swales and walkway porous pavers, plus bioretention for roof and parking area runoff 66, Increase Compared to Undeveloped Conditions Elements of Conservation Design for Cedar Hills Development (near Madison, WI, project conducted by Roger Bannerman, WI DNR and USGS) Grass Swales Wet Detention Pond Infiltration Basin/Wetland Reduced Street Width 29

30 The most comprehensive fullscale study comparing advanced stormwater controls conducted. Available at: r/2008/5008/pdf/sir_ pdf 90% of the site runoff is associated with rains between 0.2 and 3 inches in depth. These are the events that need attention when trying to reduce runoff at this site. 50% of the rains, by count, are less than 0.15 inches in depth. 30

31 Parallel study areas, comparing test with control site Cedar Hill Site Design, Crossplains WI Explanation Wetpond Infiltrations Basin Swales Sidewalk Driveway Houses Lawns Roadway Woodlot N Feet 31

32 Initially installed infiltration area had preferential flow paths and compacted soils Roger Bannerman Infiltration Basin with Compacted Soils Deep Tilled to 18 inches and Planted Native Plants to Restore Infiltration Roger Bannerman 32

33 WI DNR photos Reductions in Runoff Volume for Cedar Hills (calculated using WinSLAMM and verified by site monitoring) Type of Control Runoff Volume, inches Pre-development 1.3 Expected Change (being monitored) No Controls % increase Swales + Pond/wetland + Infiltration Basin % decrease, compared to no controls 15% increase over pre-development 33

34 Water Year Monitored Performance of Controls at Cross Plains Conservation Design Development Construction Phase Rainfall (inches) Volume Leaving Basin (inches) Percent of Volume Retained (%) 1999 Pre-construction % 2000 Active construction % 2001 Active construction % 2002 Active construction (site is approximately 75% built-out) % WI DNR and USGS data 34

35 Aerial Photo of Site under Construction (Google Earth) On-site bioretention swales Level spreaders Large regional swales Wet detention ponds Critical source area controls Pollution prevention (no Zn!) Buffers around sinkholes Extensive trail system linking water features and open space 35

36 Conservation Design Elements for North Huntsville, AL, Industrial Park Grass filtering and swale drainages Modified soils to protect groundwater Wet detention ponds Bioretention and site infiltration devices Critical source area controls at loading docks, etc. Pollution prevention through material selection (no exposed galvanized metal, for example) and no exposure of materials and products. Trail system throughout area. 36

37 A new industrial site in Huntsville, AL, has 52 approximately two acre individual building sites. Each of the sites will be served with a grass-lined bioretention channel that will carry site water to a larger swale system. The slopes of the channels vary from about 1 to 6.5%. The peak flow from each construction site was calculated to be about 16 ft 3 /sec (corresponding to the Huntsville, AL, 25 yr design storm of 6.3 inches for 24 hours). The on-site swales will also have modified soils to increase the CEC and organic matter content to protect groundwater resources. 37

38 The bare swale soil has an allowable shear stress of about 0.05 lb/ft 2. The calculated values for unprotected conditions are all much larger. Therefore, a North American Green S75 mat was selected, having an allowable shear stress of 1.55 lb/ft 2 and a life of 12 months. Check dams are needed when slopes are >5% due to high velocities. Slope Bare soil shear stress (lb/ft 2 ) Unvegetated mat shear stress, effect on soil (lb/ft 2 ) Safety factor (allowable shear stress of 0.05 lb/ft 2 ) 1% % % % Maximum velocity with mature vegetation (ft/sec) Different site subareas have different combinations of controls. Base conditions are for conventional development. Drainage Area A Proposed Stormwater Components Pond, swale, and site bioretention Annual Runoff Volume (ft 3 /year) Base Conditions With Controls 6.3 x x 10 6 (61%) B Small pond and swale 5.4 x x 10 6 (69%) C Pond and swale 2.5 x x 10 6 (68%) D (including off-site area) Off-site pond, swale, and site bioretention 11 x x 10 6 (50%) Total site 25 x x 10 6 (56%) Calculated using WinSLAMM and 40 years of rain records 38

39 Drainage Area A Proposed Stormwater Components Pond, swale, and site bioretention Annual Particulate Solids Discharges (lb/year) Base Conditions With Controls 98,000 4,400 (96%) B Small pond and swale 54,000 3,800 (93%) C Pond and swale 19,000 1,200 (94%) D (including off site area) Off-site pond, swale, and site bioretention 120,000 9,250 (92%) Total site 290,000 19,000 (93%) Conventional Development Conservation Design 39

40 Conventional Development Conservation Design Sediment Reductions Volume Reductions 40

41 Lodi, Wisconsin, Transportation Area Rain Garden Drainage Basin Area = 16 acres Paved Area = 20% City of Lodi, Columbia County WI John Voorhees Lodi Rain Garden Features Access Path Overflow Weirs Cell C Sitting Area Inlet Cell A Cell B Flow Diversion Structure John Voorhees 41

42 Flow Diversion Structure To Rain Garden Overflow to Creek J h V Rain Garden Backfill Material Growing Media Aggregate for Water Storage Underdrain Pipe Sends Excess Water to Creek John Voorhees 42

43 Soil/Peat/Sand Mixing John Voorhees Cell A Cell B John Voorhees 43

44 Cell A Cell B Cell C John Voorhees Planting Plan Scrub sprairie Plants Cell A Cell C Cell B John Voorhees 44

45 Fall 2004 Summer 2005 Spring 2005 Lodi rain garden vegetation (Planted in Spring 2004); excellent cover 6 to 15 months after planting John Voorhees Lodi, WI, Rain Garden Costs Pipe Underdrain and Endwalls $700 Flow Regulation Structure $3000 Plants $2200 Shrubs $450 Backfill $11600 Excavation $2200 Select Crushed Material/Riprap $3850 Storm Sewer and Manholes $3500 Total $4.70/sf $27500 John Voorhees 45

46 Appropriate Combinations of Controls No single control is adequate for all problems Only infiltration reduces water flows, along with soluble and particulate pollutants. Only applicable in conditions having minimal groundwater contamination potential. Wet detention ponds reduce particulate pollutants and may help control dry weather flows. They do not consistently reduce concentrations of soluble pollutants, nor do they generally solve regional drainage and flooding problems. A combination of biofiltration and sedimentation practices is usually needed, at both critical source areas and at critical outfalls. Combinations of Controls Needed to Meet Many Stormwater Management Objectives Smallest storms should be captured on-site for reuse, or infiltrated Design controls to treat runoff that cannot be infiltrated on site Provide controls to reduce energy of large events that would otherwise affect habitat Provide conventional flood and drainage controls 46

47 Combinations of Controls Needed to Meet Many Stormwater Management Objectives Smallest storms should be captured on-site for reuse, or infiltrated Design controls to treat runoff that cannot be infiltrated on site Provide controls to reduce energy of large events that would otherwise affect habitat Provide conventional flood and drainage controls Pitt, et al. (2000) 47