New England Grows February 8, (c) 2013, Chris Webb & Associates, Inc., PS 1

Transcription

1 Emerging Trends in Stormwater Management New England Grows 2013 Christopher J. Webb, PE, LEED-Fellow Chris Webb & Associates, Inc., PS, Bellingham, WA STORMWATER MANAGEMENT Emerging Big Picture Design Trends 1. Grey to Green 2. Centralized to Distributed 3. Linear to Circular STORMWATER MANAGEMENT Emerging Big Picture Design Trends 4. LID / GSI emerging as Best Available Technology Best available science suggests that a broad category of new stormwater management practices that come under the heading of low impact development (LID) or green stormwater infrastructure (GSI) can improve flow control, water quality treatment and protection of receiving waters. Accordingly, many states across the U.S. are considering adoption of LID practices. The use of LID practices will be required for managing stormwater in western Washington over the next few years as the new NPDES permit is phased in. --Washington Stormwater Center Is there a Problem here? (c) 2013, Chris Webb & Associates, Inc., PS 1

2 Introduction Goals New England Land Cover, USGS, 2006 L.I.D. Site Design Techniques: Planning (clustering, maximize density where appropriate, preserve ecologically sensitive areas, site selection, etc.) Street Geometrics (skinny streets, interconnected street grid, etc.) Disconnecting impervious i surfaces (curbless streets, t downspouts to splash blocks and not connected to a piped stormwater system, sheet flow to greatest extent possible, grass filter strips, etc.) Soil Amendments (Compost amended soils to increase water retention and reduce irrigation needs) Bioretention (or Raingardens ) Porous Pavements Rainwater Collection and Reuse Green Roofs (vegetated roof systems) Minimize concentrating stormwater Sheet flow Small drainage basins Surface conveyance Work with the soil Amended soil with compost Bioretention / raingardens Pervious pavements Approach Use smaller decentralized solutions at the source Decentralized Approach (Small Scale Systems) vs. Centralized Approach (Large Scale System) Use smaller infiltration rates over larger areas Approach Summary Create a hydraulically functional landscape. Value Created Multi-purpose infrastructure is inherently more efficient use of land and resources than single purpose infrastructure Decentralized infrastructure can be more effective because it can exploit synergies with other systems and maximize the utilization of a site s latent capacity for infiltration (c) 2013, Chris Webb & Associates, Inc., PS 2

3 Predicting future Challenges / Opportunities The future of stormwater management will Require civil/site contractors to become more like landscape contractors and vice versa Challenges/Opportunities: Training, i standards, d new business models to build these systems Stormwater practices will be increasingly made up of a network of smaller green interventions at the beginning of the pipe vs. larger grey end of pipe solutions Challenges/Opportunities: Post Construction Operations, Maintenance & Management, new business models needed to perform the service Application Trends in Puget Sound Photo by City of Maplewood MN Bioretention swales adjacent to roads and within right of way. Application of bioretention cells on single family lots increasing in the Northwest region and nationally. Construction in dense settings requires careful sequencing, staging, and TESC. Under-drains vs. overflows may be the most misunderstood & challenging design element. Application Trends in Puget Sound SEA Street project, 2nd Ave NW, from NW 117th to NW 120th Approximately 98% stormwater volume reduction compared to pre-existing street design. Last recorded discharges on 12/14/02 and 12/07. Hydrologic performance tending to exceed design expectations. Compost Amended Soil Compost Amended Soil Bioretention / Raingardens Why build healthy soil? More marketable buildings and landscapes Better site erosion control Reduced need for water and chemicals Less stormwater runoff, better water quality Healthy landscapes = satisfied customers 5 Construction Practices: Retain and protect native topsoil & vegetation where practical Restore disturbed soils, to restore healthy soil functions, by: stockpiling & reusing good quality site soil, or tilling 2-3" of compost into poor site soils, or bringing in 8" of compost- amended topsoil Loosen compacted subsoil, if needed, by ripping to 12" depth Mulch landscape beds after planting Protect restored soils from erosion or recompaction by heavy equipment What is Bioretention? Concept originated in Prince George s County, MD in early 1990 s Small depressions in the ground that receive stormwater from small basins Provide stormwater treatment and/or retention Soil, plants, and soil microbes work as a system to break down pollutants Image by AHBL from the PSAT LID technical manual (c) 2013, Chris Webb & Associates, Inc., PS 3

4 New England Grows February 8, 2013 Bioretention Water Quality Treatment pathways Stormwater volume reduction Sedimentation Filtration Phytoremediation Thermal attenuation Adsorption Volatilization Bioretention / Raingarden Public ROW Example (First in City of Bellingham, WA) Bioretention is not and effective flow control practice on till Bioretention can not be used for water quality treatment in pollutant hot spots Geotextiles necessary at the soil mix and native soil interface Stormwater Reduction (%) for Seattle Soils 100% 90% 80% 70% Reduction Bioretention Myths 60% 50% 40% 30% 20% 10% 0% 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% Ratio of Rain Garden Area to Impervious Area Till Outwash water quality treatment Bioretention integrated into site & building design (c) 2013, Chris Webb & Associates, Inc., PS Urban design example Urban design example 4

5 Bioretention / Raingarden in Urban setting (Portland, OR) POROUS PAVEMENTS Impervious Surface Reduction Strategies REINFORCED GRASS PAVEMENT Example Project Permeable (Porous) Surfaces Hardscapes Porous Concrete / Asphalt Pavements Interlocking Concrete Pavers Gravel Cellular Confinement Systems Softscapes Reinforced Grass Surfaces Grass Cellular Confinement Systems Boundary Bay Brewery, Bellingham, WA POROUS GRAVEL PAVEMENT POROUS CONCRETE PAVEMENT Impervious Surface Reduction Strategies REINFORCED GRASS / PERVIOUS CONCRETE PAVEMENT Hybrid Pervious Pavement Example Project (2006) ADA Assessible Trail Dan Godwin Center, Bellingham, WA (c) 2013, Chris Webb & Associates, Inc., PS 5

6 Example Project (Municipal Community Center) PERMEABLE ASPHALT PAVEMENT Summary Pervious Concrete Raingarden Strip Full Depth Permeable Asphalt Pavement vs. what has been used for years in noise and safety mitigation (friction course) Lower cost than pervious concrete More frequent replacements (i.e. less durable) Pervious ATB is available Raingarden Strip Pervious Concrete Firstenburg Community Center, City of Vancouver, WA INTERLOCKING CONCRETE PAVERS Types of Pavers Single Family Residential Non-Potable Water Example Project Residential Potable Water Example Project SF-RIMA UNI ECOSTONE TURFSTONE Seattle, WA, 2007 Rainwater for flushing 1 toilet in new studio 480 gallon HDPE cistern In-line upstream filter (1 mm mesh) No water system back-up (hose of needed) No pump, only gravity flow only (elevated tank 4.5 ) No downstream filtration Swinomish Indian Reservation, Skagit County, WA, built 1999 Rainwater as sole source of potable water 1,600 sf metal roof, 5,600 gal. Storage, 2 people, 20/5 micron cartridge filtration, 1/0.5 micron carbon at taps, UV disinfection Composting toilets & small greywater re-use system (c) 2013, Chris Webb & Associates, Inc., PS 6

7 Residential Potable Water Example Project Multi-Unit Residential Non-Potable Water Example Project 14-Units Zero Net Energy, Lopez Island, WA Sports Stadium Example Project Rainwater for non-potable uses (toilet flushing, clothes washers, and irrigation) 34,000 gallon central cistern Water System back-up Many green building strategies 5 micron sand filter filtration Water Right Acquired As Green Stormwater Infrastructure Green Roofs Summary Key LID Benefits Residential Commercial Water Quality Greater levels of stormwater quality are achieved than conventional treatment practices Water Quantity Greater amounts of infiltration and groundwater recharge Addresses stormwater run-off volume and not just rate Reduced potable water use via rainwater collection and reuse & using soil amendments More natural site hydrology benefits stream habitats and wetlands (c) 2013, Chris Webb & Associates, Inc., PS 7

8 Summary Key LID Benefits Aesthetics More attractive when integrated into the design Economical Efficient use of land by reduce or eliminate ponds and vaults Skinny streets are less expensive to build Stormwater treatment with bioretention is the least expensive method of stormwater treatment when used in place of landscaping On soils that infiltrate more than about 1/4 /hr. LID will typically be less expensive to build than traditional systems (c) 2013, Chris Webb & Associates, Inc., PS 8