Webcast Agenda 3/27/2014. Speaker Info. Chesapeake Bay Stormwater Training Partnership. Welcome to the Webcast

Transcription

1 Advanced Stormwater Design Webcast Series: Bioretention Dry Swales 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! Speaker Info Chesapeake Bay Stormwater Training Partnership Visit: Charlene Harper, Geosyntec, charper@geosyntec.com Dave Hirschman, Center for Watershed Protection, djh@cwp.org Cecilia Lane, Chesapeake Stormwater Network, watershedgal@hotmail.com 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 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 Poll Question #1 Tell us a little about yourselves who are you representing today? Design professional MS4 Ph 1 MS4 Phase 1 MS4 Phase 2 State government Federal government Other 1

2 Poll Question #2 What is your experience with bioretention and dry swales? Bioretention 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 Applications/Types Micro Scale Applications Drainage Area = 250 to 2,500 square feet (mostly impervious) Bioretention ti Wt Water Quality or Dry Swale Residential Lots Commercial Rooftop Urban Bioretention Residential Rain Garden Typical Scale Applications Impervious Area Treated = Up to 2.5 acres Basin Scale: Bioretention Basins Impervious Area Treated = Up to 5 acres & 2.5 acres of impervious Parking Lot Edges Parking Lot Medians Institutional Bottom of ED Pond Courtyards Right-of-way/Urban Bioretention 2

3 Linear Applications: Dry or Water Quality Swale Bioretention: How it Works Runoff flows into a bioretention facility and temporarily ponds. Water then slowly filters through the filter bed and either is collected by the underdrain and sent to the storm sewer system or infiltrates into the surrounding area. State Stormwater Performance and BMP Performance Credits Most states established a stormwater treatment volume that must be managed by a BMP; The volume is computed as the amount of runoff generated by a specified rainfall depth; The rainfall depth is defined by each state: DC, MD, NY, VA, & WV: 90 th percentile rainfall depth (approximately 1 inch); DE: Resource Protection Event (RPE) = 2.7 inches of rainfall. Designers should consult the individual state design criteria for guidance on computing the required runoff volume. 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 Zero effective impervious for 2.7 rainfall Runoff Volume Reduction (Resource Protection Event, RPE) MD On site retention using ESD of runoff from 1.0 rainfall Runoff Volume Reduction OR Impervious CN Reduction NY VA On site retention of runoff from 90 th Runoff Volume Reduction percentile rainfall (~ 1 ) Total Phosphorus Load Limit of 0.41 lbs/ac/yr (performance based on management of runoff from 1.0 rainfall) 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. Different Levels of BMP Design Level 1 Level 2 Good design to provide treatment, safety, functionality Bioretention = % Dry Swale = 40 60% Includes design enhancements for runoff reduction and/or pollutant removal: Size, treatment volume Flow path Soil media depth Vegetation plan 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 Treat Target Rainfall to meet ESD standards NY 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 3

4 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% Volume Reduction = 80% TP Reduction = 20% Total Load Reduction = 52% TP Reduction = 40% Total Load Reduction = 76% WV 55% for Design Volume Provided 100% for Design Volume Provided 24 soil media No underdrain sump Bioretention: Level 1 Red = different value from Bioretention Bioretention Level 2 Infiltration 36 soil media No underdrain Field measured soil permeability 1 /hr. Soil Testing for Infiltration Design Infiltration designs require permeable soils (typical required infiltration rate (f) = 0.52 /hr minimum, or with a factor of safety, f = 1 /hr); Designers should evaluate existing soil properties during initial site layout. In particular, areas of HSG A or B soils should be considered as primary locations for all types of infiltration. Level 2 Infiltration Sump 36 soil media Sump below underdrain pipe (12 or drain within 48 hours) Level 2 Upturned Elbow (Internal Water Storage Zone) 4

5 WV Bioretention Level 2 Extended Filtration General Level 2 Sizing Increase Treatment Volume by 25% Tv from Spreadsheet x 1.25 Dry/Water Quality Swale Dry Swales: Check Dam Details Level 1 (VA) Level 2 (VA) Runoff Reduction is a Common Theme Keys to the Kingdom for Designers Bioretention ti = % Dry Swale = 40 60% 1. Footprint on site 3. Design details 2. Credit for compliance In other words, a pretty darn good slice 5

6 1. Footprint on Site Space available for stormwater treatment Right size for the practice possibility of splitting into individual cells Figuring i out practices in series Too Small! Too Large! Just Right (probably) Sizing/Storage for Treatment Volume (Tv) 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 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 6

7 2. Credit for Compliance 3. Design Details State specific Level 1/Level 2 or other performance system Size/storage volume provided Underdrain d or no underdrain? d If underdrain, use of sump or internal water storage Soil media depth Typical Design Features Selected Key Design Issues Pretreatment stone diaphragm (typ.) 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) Ponding Depth = Side Slopes = 3:1 max (recommended) 1. Geometry 2. Getting Water In 3. Pretreatment 4. Soil Media 5. Separation Barrier Between Soil & Underdrain 6. Vegetation 1. Geometry: Long Flow Path, Good Treatment Goal: create a long flow path from inlet to outlet 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 7

8 2. Options to Get Water In Water Can t Get In Curb Cuts Notice Sediment? Sheet Flow Pipe Flow Inflow Should Be Inevitable : e.g., 2 4 drop from pavement edge 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 Other Pretreatment (types) 2 3 Some State Specs Have Pre Treatment Details (example: VA, curb inlets, concentrated flow) Forebay 2. Stone/RipRap Apron 3. Stone Flow Spreader 4. Grass Filter Strip 5. Grass Channel 8

9 4. Soil Media 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 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) 5. Separation Barrier Between Soil & Underdrain Filter Fabric * See most recent Virginia Bioretention Spec #9 (2013) for most comprehensive discussion of soil media specifications Use Transition Stone Instead Soil Media Pea Gravel Over Underdrain Stone 9

10 6. Vegetation Vegetation: Too much, too little what s the intended palette? Bioretention Meadow - Heritage Baptist Church, Annapolis, MD Three Quick Principles for Bioretention Vegetation A. Context 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.) Institutional, Medium Visibility Public, High Visibility Small-Scale, Residential Bio Typologies Typology: The taxonomic classification of characteristics common to buildings or spaces Dry/Water Quality Swale Vegetation Can Vary PERENNIAL GARDEN TREE TURF PERENNIAL - SHRUB TREE SHRUB MULCH Landscaped More Complicated More Maintenance Grass Simple Less Maintenance 10

11 B. Fill Surface Area Mix of Herbaceous, Shrubs Mulch is a temporary surface cover 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 It s Always Pretty in the Beginning, But... But You Need To Keep It Looking Good! Q & A 11

12 Design Adaptations On Slopes: Dry/Water Quality Swale Check dams Break into cells linked with conveyance Longitudinal Slope = 0.5% 2%, Up to 4 5% with check dams Level 2 Design: Effective slope (w/check dams)< 1% 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. Karst Preliminary & Detailed Site Investigations Soil Borings Site Planning Techniques Additional BMP Design Criteria tegory/publications/csn technicalbulletins/ Impermeable Liner vs. No Liner? 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 bd k( (e.g., within 3 ) Stormwater hotspot land use Photo Courtesy: James Madison University 12

13 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 Liners Limit Practice to Level 1 Photo Courtesy: James Madison University Coastal: Flat Terrain 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 technical bulletins/ Internal Water Storage (IWS) Zone IWS Using Controlled Underdrains 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:

14 Ultra Urban/Street Bioretention 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) Flow Thru Planters Solutions for Drops, Safety Concerns Counted as Level 1 design Include underdrains and 30 minimum media Source: LuGay Lanier, Timmons Group Source: streets victoria bc.html 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 Steel Wool Iron Filings ~½ inch thick ~C33 Concrete Sand Source: Andy Erickson, Saint Anthony Falls Laboratory, Univ. of Minnesota 14

15 MN Filter Trenches (Prior Lake MN) MN Filter Bioretention (Carver County, MN) Construction Inspection Critical Inspection Points Photo Courtesy: A. Erickson Photo Courtesy: W. Forbord Ready to Install? Inverts/Elevations Inlets/Curb Cuts MN Filter Bioretention (Maplewood Mall, MN) Photo Courtesy: A. Erickson MN Filter Weir (Vadnais Heights, MN) Photo Courtesy: VLAWMO and EOR Underdrain d (pipe material, il perforations) Filter media Side Slope Grading Secondary E&S Measures Plants Bioretention in Karst Source: Andy Erickson, Saint Anthony Falls Laboratory, Univ. of Minnesota Bioretention ESC Tips Typical Construction Problems 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! Installed too early during construction Improper soil mix Stone too high at inlet blocks flow Small grade changes divert flow from inlet Maintenance 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 15

16 Visual Indicator Approach for Bioretention INLET ZONE Bioretention from above OUTLET ZONE BED AND VEGETATION 2 3 SIDE SLOPES 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 Conclusions Understand design objectives, sizing, compliance (keys to the kingdom) Consult state specific specifications for performance & design details Consider design adaptationsfor tricky sites or geographies Design with maintenance in mind, especially selection of vegetation Use available resources (Visual Indicators) for maintenance Q & A 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 Stream Restoration TMDL 5 May 1 Advanced Stormwater Design Infiltration 6 May 8 MS4 Implementers and the Bay TMDL Urban Nutrient Management 7 May 29 Advanced d 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 TBD TMDL 11 June 26 Advanced Stormwater Design Grass Channels, Filter Strips & Disconnections 16

17 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 Evaluation Please take a few moments to answer our 6 question survey to help us better serve your needs in our 2014 webcast series. / /386PG25 We use this information to report it to assess our work, your needs and to report it to our funders for future webcasts! Bioretention Design Example 3 acre commercial development; 1.4 acres of impervious, 1.2 acres of managed turf, 0.4 acres open space Sloping site General direction of site grade Runoff Reduction Spreadsheet (VA version) Treatment Volume (Tv) = 5,844 cubic feet TP Load = 3.67 lbs/acre/year TN Load = lbs/acre/year VA TP Reduction to Meet 0.41 lbs/acre/year = 244lb 2.44 lbs Treat 1.4 acres impervious with Bioretention Level 2 Runoff Reduction Volume = 3,862 cubic feet TP Reduction = 2.73 > 2.44 required TN Reduction = Bioretention Level 2: RR Volume = 3,862 cubic feet Level 2 Design = 3,862 x 1.25 = 4,828 cubic feet Additional Ponding Surface Area for Water Quality + Channel/Flood Protection Volume Additional Ponding Additional Ponding (3 ft. soil x 0.25) + (1 ft. gravel x 0.40) + (0.5 ft. ponding x 1.0) = 1.65 ft. Surface Area = 4,828 cf / 1.65 ft. = 2,926 ft 2 6 Ponding Increase ponding area by up to 50% Decrease soil media SA from 2,926 to 2,600 ft 2 New Ponding Area = 2,600 ft 2 + 1,300 ft 2 = 3,900 ft 2 for water quality + channel/flood protection trade off between overall footprint and cost of soil media New Volume = (3,900 x 1.0) + (2,600 x 3 x 0.25) + (2,600 x 1.0 x 0.40) = 4,940 ft 3 > 4,828 ft 3 Divide into 4 cells = 1,235 ft 2 per cell 17

18 Break Into Cells Flexibility & Reduce Flow to any one cell Where To Find Design Resources: Virginia Laws, Regulations, Permits: Virginia Dept. of Environmental Quality, Stormwater: nagement.aspx BMP Specifications: Virginia Stormwater BMP Clearinghouse, Non Proprietary (Bioretention = Specification #9): Can Decrease Bioretention Footprint By: Using Level 1 design + additional BMP (e.g., grass swale) Not add additional ponding surface area Increase surface ponding depth to as much as 12 Use other BMPs in treatment train using spreadsheet Where To Find Design Resources: West Virginia Laws, Regulations, Permits: West Virginia Dept. of Environmental Protection: w_home.aspx BMP Specifications: West Virginia Stormwater Management & Design Guidance Manual (Bioretention = Specification 4.2.3): ges/stormwatermanagementdesignandguidancemanual.aspx Where To Find Design Resources: D.C. Stormwater Rule: District Department of the Environment: BMP Specifications: D.C. Stormwater Management Guidebook (Bioretention = Specification 3.6): Where To Find Design Resources: Delaware Laws, Regulations, Permits: Department of Natural Resources & Environmental Control: ater.aspx BMP Specifications: Sediment & Stormwater Technical Document (Bioretention = Appendix ): al_document.aspx Where To Find Design Resources: Maryland Laws, Regulations, Permits: Department of the Environment: ManagementProgram/SedimentandStormwaterHome/Pages/ Programs/WaterPrograms/SedimentandStormwater/home/in dex.aspx BMP Specifications: Maryland Stormwater Design Manual (Bioretention = Section 3.4, Stormwater Filtering Systems): ManagementProgram/MarylandStormwaterDesignManual/Pa ges/programs/waterprograms/sedimentandstormwater/stor mwater_design/index.aspx 18

19 Where To Find Design Resources: Pennsylvania Where To Find Design Resources: New York Laws, Regulations, Permits: PA Department of Environmental Protection: ormwater_management/21377 BMP Specifications: PA Stormwater Best Management Practices Manual (Chapter 6.4.5, Rain Garden/Bioretention): st_management_practices_manual/21383 Laws, Regulations, Permits: NY Department of Environmental Conservation: BMP Specifications: NY State Stormwater Management Design Manual: Bay Wide Design Resources Design Guidance for Karst, Coastal, Urban/Redevelopment: Chesapeake Stormwater Network, Technical Bulletins: bulletins/ 19