FULL CYCLE BIORETENTION Sustaining Performance Over Decades
Welcome to the Webcast • 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!
Let’s Get Interactive Today ! • We want to get your feedback on how to perfect bioretention, so please submit your comments in the chat box located to the left of the slides . • We will read and respond to as many comments as possible during our three feedback breaks today • We want to acknowledge insights provided by Ted Scott, Dave Hirschman, Shannon Lucas and many local practitioners in the Bay watershed last year * Although any really bad ideas you hear today are the sole responsibility of CS N
Chesapeake Bay Stormwater Training Partnership To learn how you can have access to: FREE Webcasts Free design, inspection & maintenance workshops Intensive stormwater seminars Direct On-site technical assistance Self guided web-based learning modules Visit: www.chesapeakestormwater.net
Upcoming Webcasts Wednesday, March 15: • Users Guide to Urban BMPs in the Chesapeake Bay Thursday, March 30 : • New Crediting Approaches: Impervious Cover Disconnection and CMAC Thursday, April 20: • Fall Leaf Collection and Street Nutrient Loads Register here: http://chesapeakestormwater.net/events/categories/webcasts/2017-webcast-series/
2017 Help us recognize the best BMP installed in the Chesapeake Bay Watershed Voting opens February 27 th ! Check the finalists: http://chesapeakestormwater.net/the-bubbas/2017-bubbas-2/
Poll Question #1 Tell us a little about yourselves…who are you representing today? • Local government • Private sector • Regulatory agency • Non-profit • Academia • Other… tell us in the chat box
Poll Question #2 Tell us how this webcast is relevant to you: • I design bioretention projects • I am involved in bioretention construction or landcaping • I inspect or maintain bioretention • I am a planner and use BMPs to account for load reductions • I am a researcher • I am generally interested in the topic • Other
Poll Question # 3 How satisfied are you with the typical bioretention area installed in your community? • Very satisfied • Satisfied, but see a few problems • Not satisfied, see a lot of problems • Very dissatisfied • No opinion
Today’s Agenda • Evolution of bioretention practice • What we have learned in the last five years • The Full-Cycle Approach: Applying it to the next generation of the bioretention practice • Audience feedback
Bioretention: How it Works 11
Key Bioretention Design Elements • Ponding area • Filter media • Pea gravel • Overflow • Vegetation • Optional: – Underdrain + stone – Infiltration sump 12
Evolution of Bioretention • 1992: PG County Design Specification • 1996: CWP Design of SW Filtering Systems • 2000: MD Stormwater Manual • 2008: Baywide Design Specification • 2009-2013 : Bay State Stormwater Manuals • 2017 : ????
Going Beyond the 2008 Bay-wide Design Specification
Why are we revisiting bioretention? • Now the #1 BMP installed in the Bay • State design specs are 5 to 10 years old • Flood of new research in the last 5 years • Critical feedback from inspectors and maintainers • Many older BR projects are no longer meeting intended functions
Full Cycle Bioretention 1.Monitoring 2.Assessment 7. Makeover 6.Maintenance 3.BMP Design 5.Inspection 4.Construction
What is the Full Cycle Approach? 1. Establish minimum performance objectives for the practice 2. Ensure the practice is feasible for the site 3. Meet design criteria to maintain performance over entire cycle 4. Be properly constructed and established 5. Inspect using visual indicators 6. Use landscape contractors to maintain function over time 7. Perform a “make - over” when functions diminish
What have we learned in the past few years? • Research on bioretention performance – Runoff reduction – Pollutant removal – BR components that influence performance (+/-) • Operational experience – What design elements are most problematic? – What steps in the cycle are most critical? – What is a sustainable plant community?
Performance: Runoff Reduction • Runoff Reduction (RR) is most important outcome in bioretention design • Infiltration, evapotranspiration and extended filtration can reduce annual runoff volume by 40 to 70%, depending on underlying soils • Internal water storage zone design can further boost RR in bioretention area s
Maximizing Runoff Reduction Vegetation Underdrain system with Internal Water Storage
Plants and Runoff Reduction • While direct plant uptake does not contribute much to pollutant removal, they are essential for runoff reduction and practice sustainability: – The evapotranspiration pump – Dense root networks maintain media porosity – Plant detritus is carbon source for denitrification and enhanced microbial growth • Existing adjustor curves can estimate how increased runoff reduction improves pollutant load removal in bioretention areas
Key Pollutant Removal Factors • Bioretention is effective in removing range of pollutants, including toxics, bacteria and nutrients • Next generation design should be capable of meeting load removal targets • Media and vegetation matters • We are not achieving denitrification reliably
Standard Bioretention PON DON NO3 NO3 NH4 DE DENITRIFI FICATION DON MI MINERALIZATION PB N2 AM AMMONIFICATION NIT NITRIFICATION NO3 NO3 No mechanism for full N removal in the standard bioretention design Source: Allen Davis
Media Matters • Current media recipe meets performance objectives • Research shows nutrient removal can be boosted when PEDs are added to the basic bioretention media recipe • The removal boost is usually greater for TP than TN • On the other hand, low or even negative nutrient removal has been reported for media recipes that rely on compost or fast-decomposing organic matter
Vegetation Matters • Vegetative cover is important both above and below ground • The root network enhances microbial activity in the media to transform nutrients and maintain its hydraulic performance • Plant detritus is the long term carbon source needed for denitrification • Periodic harvesting may help with nutrient removal from system. • Need more research on best plant species for bioretention
Critical Design Elements for Better Performance Positive Factors • Media • Internal Water Storage Zone • Plant cover and root depth Neutral or Negative Factors • Mulch • Plant uptake (not much) • Ponding volume
Problems Encountered in the Field • Poor inflow • Poor internal geometry • Questionable value of mulch • Big drainage areas = more problems • Filter bed failures • Scrubby plant community
Performance Issues Observed in Field General Performance Problems with Bioretention (n = 40) Need Maintenance 33% No Pre-Treatment 25% Inadequate Vegetation 23% Short-Circuiting of Treatment 18% Sediment Deposition 18% Excessive Vegetation 15% Inappropriate Media 8% Clogged Soil Media 8% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Source: CWP (2008) James River Basin 28
Most of our current inlet designs don’t work well in the real world and actually create much of the maintenance burden associated with bioretention We have a “goldilocks” problem when it comes to managing such a small elevation drop, especially from curb cut inlets
Bioretention Inlet Failures 30
Filter Bed Failures 31
Mulch is an expensive permanent cover that is real hard to maintain because it floats Severe 32
Bioretention with really large CDAs appear prone to failure
Knucklehead designs
FEEDBACK BREAK
Full Cycle Bioretention 1.Monitoring 2.Assessment 7. Makeover 6.Maintenance 3.BMP Design 5.Inspection 4.Construction
Bioretention need to be managed over decades • Every step in the bioretention management cycle is important to keep them working • Some key steps: – Confirm underground features during construction – Establish successful plant community – Operate regular seasonal maintenance regime – Use triggers to compel non-routine maintenance or makeovers at individual sites
Performance Targets
Targets for Bioretention Performance Bioretention areas should consistently achieve the following over their entire life-cycle • Runoff Reduction : Reduce half of the stormwater volume going into the bioretention area, from on an annual basis • Pollutant Load Removed – 90%: sediment – 75%: toxins, bacteria and trace metals – 50%: nutrients (N and P)
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