Advanced Stormwater Design Webcast Series: Bioretention Dry Swales

Transcription

1 Advanced Stormwater Design Webcast Series: Bioretention Dry Swales

2 Welcome to the Webcast To Ask a Question Submit your question in the chat box located to the left of the slides. We will answer as many as possible during Q&A. To Answer a Poll Question Simply select the preferred option. For those viewing this session alongside several colleagues, respond in a manner that represents your organization as a whole. We ARE Recording this Session All comments and questions will be recorded and included in the archives. We will notify you as soon as the recording and related resources are loaded on the web. We Appreciate Your Feedback Fill out our evaluations our funders need to hear it!

3 Speaker Info Charlene Harper, Geosyntec, Dave Hirschman, Center for Watershed Protection, Cecilia Lane, Chesapeake Stormwater Network,

4 Chesapeake Bay Stormwater Training Partnership Visit: To learn how you can have access to: Discounted Webcasts Free One-day design workshops Intensive master stormwater design seminars Direct On-site technical assistance Self guided web-based learning modules

5 Webcast Agenda Bioretention Applications & Scales Performance Level 1 & 2 Design, Design Variations Keys to the Kingdom for Designers Key Design Issues Design Adaptations & Some Newer Stuff Construction Maintenance Conclusions Design Example State Specific Resources

6 Poll Question #1 Tell us a little about yourselves who are you representing today? Design professional MS4 Phase 1 MS4 Phase 2 State government Federal government Other

7 Poll Question #2 What is your experience with bioretention and dry swales? Just getting to know the practice Have designed several Have designed many Have reviewed plans, but don t have design experience Have inspected them: construction & post-construction Have driven my car into these things

8 Bioretention

9 Applications/Types Bioretention Water Quality or Dry Swale Urban Bioretention Residential Rain Garden

10 State Performance Standards State Regulatory Performance Standard 1 BMP Performance Credit 1 DC On-site retention of runoff from 1.2 rainfall Runoff Volume reduction DE MD NY VA Zero effective impervious for 2.7 rainfall (Resource Protection Event, RPE) On-site retention using ESD of runoff from 1.0 rainfall On-site retention of runoff from 90 th percentile rainfall (~ 1 ) Total Phosphorus Load Limit of 0.41 lbs/ac/yr (performance based on management of runoff from 1.0 rainfall) Runoff Volume Reduction Runoff Volume Reduction OR Impervious CN Reduction Runoff Volume Reduction Total TP Load Reduction (Runoff Volume + Pollutant Removal) WV On-site retention of runoff from 1.0 rainfall Runoff Volume Reduction 1 Some states may include watershed specific pollutant load reduction requirements for select parameters, e.g., TP or TSS, in addition to volume reduction.

11 Different Levels of BMP Design Level 1 Level 2 Good design to provide treatment, safety, functionality Includes design enhancements for runoff reduction and/or pollutant removal: Size, treatment volume Flow path Soil media depth Vegetation plan Bioretention = % Dry Swale = 40 60%

12 Bioretention Performance Credit State Level 1 Level 2 DC 60% of Storage Volume Provided 100% of Storage Volume Provided DE 50% of Retention Storage 100% of Retention Storage MD NY Treat Target Rainfall to meet ESD standards Volume Reduction = 100% of Retention Storage VA Volume Reduction = 40% TP Reduction = 25% Total Load Reduction = 55% Volume Reduction = 80% TP Reduction = 50% Total Load Reduction = 90% WV 60% for Design Volume Provided 100% for Design Volume Provided

13 Dry/Water Quality Swale Performance Credit State Level 1 Level 2 DC 60% of Storage Volume Provided DE 25% of Retention Storage (C/D Soils) 50% of Retention Storage (A/B Soils) MD Treat Target Rainfall to meet ESD standards NY? VA Volume Reduction = 40% TP Reduction = 20% Total Load Reduction = 52% Volume Reduction = 80% TP Reduction = 40% Total Load Reduction = 76% WV 55% for Design Volume Provided 100% for Design Volume Provided Red = different value from Bioretention

14 24 soil media No underdrain sump Bioretention: Level 1

15 Bioretention Level 2 -- Infiltration 36 soil media No underdrain Field-measured soil permeability 1 /hr.

16 Level 2 -- Infiltration Sump 36 soil media Sump below underdrain pipe (12 or drain within 48 hours)

17 Level 2 Upturned Elbow (Internal Water Storage Zone)

18 WV Bioretention Level 2 Extended Filtration

19 General Level 2 Sizing Increase Treatment Volume by 25% Tv from Spreadsheet x 1.25

20 Dry/Water Quality Swale Level 1 (VA) Level 2 (VA)

21 Keys to the Kingdom for Designers 1. Footprint on site 2. Credit for compliance 3. Design details

22 1. Footprint on Site Space available for stormwater treatment Right size for the practice possibility of splitting into individual cells Figuring out practices in series

23 Too Small!

24 Too Large!

25 Just Right (probably)

26 Sizing/Storage for Treatment Volume (Tv) η = 1.0 η = 0.25 η = 0.40 Treatment Volume (Tv) = (ponding* x 1.0) + (soil x 0.25) + (gravel x 0.40) Dry/Water Quality Swale Ponding = Storage behind check dams Some State-Specific Sizing Methods Apply

27 Increase Ponding Footprint: Extra Storage for Flood/Channel Protection 50% increase if ponding is 6 or less 25% increase if ponding is between 6 and 12 Additional Surface Ponding Additional Surface Ponding

28 2. Credit for Compliance State-specific Level 1/Level 2 or other performance system Size/storage volume provided Underdrain or no underdrain? If underdrain, use of sump or internal water storage Soil media depth

29 3. Design Details

30 Typical Design Features Pretreatment stone diaphragm (typ.) Ponding Depth = 6 12 Side Slopes = 3:1 max (recommended) Soil Media = Choker Layer = 2-4 of sand over 2 choker stone 4 6 Underdrain Pipes Underdrain Layer With 12 Stone Sump Below Underdrain Pipes (Level 2 Design) 12

31 1. Geometry 2. Getting Water In 3. Pretreatment 4. Soil Media 5. Separation Barrier Between Soil & Underdrain 6. Vegetation Selected Key Design Issues

32 1. Geometry: Long Flow Path, Good Treatment Goal: create a long flow path from inlet to outlet

33 Geometry: Short Flow Path, Less Treatment Outlet Last curb cut These practices lack of storage and treatment due to: Proximity of inflow to outflow Outlet structure flush with filter surface Direct (almost) conveyance from inlet to outlet

34 2. Options to Get Water In Curb Cuts Sheet Flow Pipe Flow

35 Water Can t Get In Notice Sediment?

36 Inflow Should Be Inevitable : e.g., 2 4 drop from pavement edge

37 3. Pretreatment Nature of pretreatment depends on size of bioretention area and type of flow it experiences Concentrated flow: two cell design with a small trapping forebay and level spreader Sheet flow: grass filter strip, stone diaphragm, stone ring berm 1. Forebay

38 Other Pretreatment (types) Forebay 2. Stone/RipRap Apron 3. Stone Flow Spreader 4. Grass Filter Strip 5. Grass Channel

39 Some State Specs Have Pre-Treatment Details (example: VA, curb inlets, concentrated flow)

40 4. Soil Media

41 Understand Objectives of Soil Media Maintain adequate soil permeability (saturated hydraulic conductivity, or Ksat), while... Providing enough fines to adsorb pollutants (e.g., phosphorus), while... Providing enough organic matter to support the intended vegetation, at least during initial plant establishment

42 Soil Media Specifications Loamy Course Sand < 10% Clay Silt + Clay = 10 to 20% Silica-Based Sand > 75% course or very course Organic = 3 to 5% dry weight basis (Walkley-Black Method) = peat moss, humus, compost, or equiv. Ksat = 1-2 inches/hour (new mix can be a lot more) Available Soil P = Low or Medium (Mehlich I or III test) Cation Exchange Capacity 5.0 meq/100 g Depth = inches, depending on Level1 or 2 (48 in tree planting holes) * See most recent Virginia Bioretention Spec #9 (2013) for most comprehensive discussion of soil media specifications

43 5. Separation Barrier Between Soil & Underdrain Filter Fabric

44 Use Transition Stone Instead

45 Soil Media Pea Gravel Over Underdrain Stone

46 6. Vegetation Bioretention Meadow - Heritage Baptist Church, Annapolis, MD

47 Vegetation: Too much, too little what s the intended palette?

48 Three Quick Principles for Bioretention Vegetation A. Select vegetation for site context B. Plan to fill up the filter bed surface area with vegetation C. Keep the plant palette simple and understandable (to maintenance crews, the public, etc.)

49 A. Context Institutional, Medium Visibility Public, High Visibility Small-Scale, Residential

50 Bio-Typologies Typology: The taxonomic classification of characteristics common to buildings or spaces PERENNIAL GARDEN TREE TURF PERENNIAL - SHRUB TREE SHRUB MULCH

51 Dry/Water Quality Swale Vegetation Can Vary Landscaped More Complicated More Maintenance Grass Simple Less Maintenance

52 B. Fill Surface Area Mix of Herbaceous, Shrubs Mulch is a temporary surface cover

53

54 C. Keep Plant Palette Simple 2 4 Species (in most cases) Plan should specify desired plant community/outcome and how maintenance can contribute to this outcome Think about how maintenance crews will distinguish intended plants from weeds

55 It s Always Pretty in the Beginning, But...

56 But You Need To Keep It Looking Good!

57 Q & A

58 Design Adaptations

59 On Slopes: Dry/Water Quality Swale Check dams Break into cells linked with conveyance Longitudinal Slope = 0.5% -- 2%, Up to % with check dams Level 2 Design: Effective slope (w/check dams)< 1%

60 Spacing of Check Dams Swale Longitudinal Slope LEVEL 1 LEVEL 2 Spacing 1 of 12-inch High (max.) Check Dams 2, 3 to Create an Effective Slope of 2% Spacing 1 of 12-inch High (max.) Check Dams 2, 3 to Create an Effective Slope of 0 to 1% 0.5% 200 ft. to 1.0% 100 ft. to 1.5% 67 ft. to 200 ft. 2.0% 50 ft. to 100 ft. 2.5% 200 ft. 40 ft. to 67 ft. 3.0% 100 ft. 33 ft. to 50 ft. 3.5% 67 ft. 30 ft. to 40 ft. 4.0% 50 ft. 25 ft. to 33 ft. 4.5% 4 40 ft. 20 ft. to 30 ft. 5.0% 4 40 ft. 20 ft. to 30 ft.

61 Karst Preliminary & Detailed Site Investigations Soil Borings Site Planning Techniques Additional BMP Design Criteria tegory/publications/csn-technicalbulletins/

62 Impermeable Liner vs. No Liner? Photo Courtesy: James Madison University

63 Use A Liner For: Larger drainage areas (e.g., > 0.5 acre) Higher volumes of water Based on advanced soil/geotechnical work, if invert (bottom) is close to bedrock (e.g., within 3 ) Stormwater hotspot land use

64 Consider No Liner For: Smaller practices (drainage areas < 0.5 acre) Advance soil/geotechnical work shows adequate soil column above bedrock (e.g., at least 3 feet to practice invert) Practices with underdrains If necessary, make practice shallower: 6 of surface ponding 18 of soil media

65 Liners Limit Practice to Level 1 Photo Courtesy: James Madison University

66 Coastal: Flat Terrain

67 Coastal Plain Bioretention Shallow it up if there are high water table or shallow head concerns: 6 ponding, of soil media Use more linear designs Use coastal plain plants, possibly more wet-footed, salt-tolerant

68 Internal Water Storage (IWS) Zone For practices with nitrogen removal objective: Incorporate internal water storage (upturned elbow), OR Use suspended underdrain with infiltration sump Check nitrogen content of soil media Source:

69 IWS Using Controlled Underdrains

70 Ultra-Urban/Street Bioretention

71 Ultra-Urban/Street Bioretention Clearly define treatment, runoff capture targets Utilities: dry & wet Match inverts to existing storm sewer may have to use upturned elbow underdrains Know the street geometry codes: turning radii, minimum widths, etc. Where needed, add safety features for drops (e.g., fences, curbing)

72 Flow-Thru Planters Counted as Level 1 design Include underdrains and 30 minimum media Source: LuGay Lanier, Timmons Group

73 Solutions for Drops, Safety Concerns Source:

74 Newer Stuff: Better Phosphorus Removal (include dissolved phase) Not Widespread in Bay Region...but up and coming? Adding iron/water treatment residuals to soil mix Research from University of MN and elsewhere

75 Steel Wool Iron Filings ~½ inch thick ~C33 Concrete Sand Source: Andy Erickson, Saint Anthony Falls Laboratory, Univ. of Minnesota

76 MN Filter Trenches (Prior Lake MN) MN Filter Bioretention (Carver County, MN) Photo Courtesy: A. Erickson Photo Courtesy: W. Forbord MN Filter Bioretention (Maplewood Mall, MN) MN Filter Weir (Vadnais Heights, MN) Photo Courtesy: A. Erickson Photo Courtesy: VLAWMO and EOR Source: Andy Erickson, Saint Anthony Falls Laboratory, Univ. of Minnesota

77 Construction Inspection Critical Inspection Points Ready to Install? Inverts/Elevations Inlets/Curb Cuts Underdrain (pipe material, perforations) Filter media Side Slope Grading Secondary E&S Measures Plants Bioretention in Karst

78 Bioretention ESC Tips Block inlets to off-line bioretention cells Install temporary diversions for on-line cells Install silt fence to filter sheet flow Rapidly stabilize cut side-slopes Work from the sides Work quickly!

79 Typical Construction Problems Installed too early during construction Improper soil mix Stone too high at inlet blocks flow Small grade changes divert flow from inlet

80 Maintenance

81 Performance Issues Observed in Field General Performance Problems with Bioretention (n = 40) Need Maintenance 33% No Pre-Treatment Inadequate Vegetation Short-Circuiting of Treatment Sediment Deposition Excessive Vegetation 25% 23% 18% 18% 15% Inappropriate Media Clogged Soil Media 8% 8% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Source: CWP (2008) James River Basin

82 Visual Indicator Approach for Bioretention

83 INLET ZONE Bioretention from above OUTLET ZONE BED AND VEGETATION SIDE SLOPES

84 Visual Indicators Sequence No. Zone INDICATOR 1 Inlet Inlet Obstruction 2 Inlet Erosion at Inlet INLET ZONE 3 Inlet Pretreatment 4 Inlet Structural Integrity, Safety Features 5 Perimeter Surface Area 6 Perimeter Side slope Erosion PERIMETER ZONE 7 Perimeter Ponding Volume 8 Bed Bed Sinking 9 Bed Sediment Caking 10 Bed Standing Water 11 Bed Ponding Depth BED ZONE 12 Bed Mulch Depth/Condition 13 Bed Trash 14 Bed Bed Erosion 15 Vegetation Vegetative Cover 16 Vegetation Vegetative Condition VEGETATION ZONE 17 Vegetation Vegetative Maintenance 18 Outlet Outlets, Underdrains, Overflows OUTLET ZONE

85 Conclusions Understand design objectives, sizing, compliance (keys to the kingdom) Consult state-specific specifications for performance & design details Consider design adaptations for tricky sites or geographies Design with maintenance in mind, especially selection of vegetation Use available resources (Visual Indicators) for maintenance

86 Q & A

87 CSN s 2014 Webcast Series No. Date Series Topic 2 March 27 Advanced Stormwater Design Bioretention & Dry Swales 3 April 3 Advanced Stormwater Design Permeable Pavement 4 April 24 MS4 Implementers and the Bay TMDL Stream Restoration 5 May 1 Advanced Stormwater Design Infiltration 6 May 8 MS4 Implementers and the Bay TMDL Urban Nutrient Management 7 May 29 Advanced Stormwater Design The Real Dirt! (Soils and Soil Amendments) 8 June 5 Advanced Stormwater Design Constructed Wetlands 9 June 12 Advanced Stormwater Design Rainwater Harvesting 10 June 19 MS4 Implementers and the Bay TMDL 11 June 26 Advanced Stormwater Design Grass Channels, Filter Strips & Disconnections TBD

88 Webcast Resources Virginia s Stormwater Design Specification No 9: Bioretention Design Specification No 10: Dry Swales Bioretention Illustrated: A Visual Guide for Constructing, Inspecting, Maintaining and Verifying the Bioretention Practice Bioretention Illustrated App Internal Water Storage (IWS) for Bioretention

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