Rainwater Management an issue for the 21 st Century. Hydrological Cycle

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1 Canadian Society of Landscape Architects CONGRESS 2014 Rainwater Management an issue for the 21 st Century Don Crockett, BCSLA, CSLA Principal, Golder Associates Ltd. May 2014 Hydrological Cycle PRE- URBAN DEVELOPMENT Deep absorbent organic soils Leaf and other organic mulch promotes infiltration Vegetative cover: Tree canopy, stems intercept rainwater Evapotranspiration Water infiltrates into subsoils and creates Base Flows that feed small tributaries Water is cooled, cleaned, and helps sustain aquatic life 1

2 Hydrological Cycle Changing Climate More severe weather Hotter, drier summers Reduced base flows in streams Neocalanus sp., a sub-arctic copepod high in lipids, is an important food source for juvenile salmon. More stresses on aquatic ecosystems Cohen Commission: Record low Sockeye salmon numbers returning to the Fraser River in 2009 was attributed not so much to loss of habitat, but as a result of warmer temperatures in many of the tributaries that affected food supply for juvenile salmon. Pressure for Increased Urban Density Compounding Factors Vancouver, British Columbia 2

3 Rainwater: Urbanization Impacts Increased Impervious Areas: Hard surfaces such as roofs, roads, paving replace absorbent organic soils. Natural processes are interrupted. Concentrated Drainage: = Erosion damage, water quality issues (including temperature) Rapid Drainage: = reduced base flows Mitigate Hydrologic Impacts of Development Volume Reduction Capture everyday rainfall events at source and infiltrate, evaporate, transpirate or re-use it. Detention Control Detain post-development runoff to pre-development (natural forested condition) levels for the mid-sized storm events Conveyance Provide safe conveyance for extreme runoff events Water Quality Control Treat everyday event 3

4 Rainfall Patterns Distribution of Burnaby Mountain Rainfall 80 75% Percentage of Annual Rainfall Volume % 4% 0 less than 35 mm 35 mm to 70 mm greater than 70 mm Rainfall Event* Size *refers to 24-hr rainfall Rainfall Capture Volume (93%) Runoff Control Volume (7%) Mitigate Hydrologic Impacts of Development Percentage of Annual Volume RAINFALL SPECTRUM LIGHT SHOWERS 75% Large Storms 20% Extreme Storms 5% SITE INTEGRATED STRATEGY NEIGHBOURHOOD WATERSHED KEEP RAIN ON SITE Infiltrate or Harvest Small Storms at the Source to Reduce Total Runoff Volume DELAY THE RUNOFF Provide Storage to Control the rate of Runoff from Large Storms REDUCE FLOODING Ensure that the Downstream System can Safely Convey Extreme Storms Water Balance Modeling Conventional Hydrologic Modeling 4

5 Integrated Stormwater Management Planning Avoid this Facilitate this Preserve this But stormwater impacts need to decrease Annual Rainfall as Runoff 70% 60% 50% 40% 30% 20% 10% Improve Watershed Trend Successful only If Stormwater Source Controls required for all new construction and redevelopment cycle Source Control complexity varies to meet ISMP goals Year 5

6 Rainwater Management starts with Land Use Planning TOOLS: The Water Balance Model Not-for-profit website designed to assist with calculations for inclusion of development source controls to reduce impacts to watersheds. Rainwater Management starts with Land Use Planning 12 6

7 Consider the Ecological Network 13 Land Use, Topography, and Rainwater 7

8 Integrated Stormwater and Open Space Integrated Stormwater and Neighbourhoods 16 8

9 Burnaby Watersheds Opportunity: use stormwater management smart practices to manage effective impervious area 70% impervious area 59% impervious area Single Family and Two Family locations 35% impervious area Watershed Pervious and Impervious Areas TOOLS Using GIS, we are quantifying rooftops, driveways, roads, as well as trees and yards Single family neighbourhoods also need watershed management as they redevelop Land Use changes over time, consider changes to impervious areas 9

10 Multiple solutions... Stormwater Source Controls UniverCity, Burnaby Integrate with the Neighbourhood: Absorbent Landscapes Green roofs over parking Narrow pavements Pervious paving Infiltration swales Topsoil re-use and compost Watercourse daylighting Detention Ponds and Wetlands Integrated Stormwater Management Planning Stormwater Source Controls absorbent landscapes pervious paving greenroof rain-garden Infiltration swale street-trees wetland & bio-filter 10

11 Absorbent Landscape 1. Crown Interception 2. Throughfall and Stemflow 3. Evapotranspiration 4. Soil Water Storage 5. Soil Infiltration 6. Surface Vegetation 7. Organics and Compost 8. Soil Life 9. Interflow 10. Deep Groundwater 11. Water Quality Improvement 12. Impermeable Surfaces and Surface Runoff Stormwater Variables of Absorbent Landscapes A schematic representation of the 12 stormwater variables of absorbent landscape. Keeping these variables in balance is the key to successful stormwater source control using absorbent landscape. Absorbent Landscapes Soil / Compost Mixes Holds +/- 20% water 175mm depth of absorbent soil stores and slowly releases about 35mm rainfall 11

12 Absorbent Landscapes Install mulch to promote infiltration Absorbent Landscapes Install mulch to promote infiltration Rainfall Storage in Soil is 7% to 18% of Soil Volume Infiltration rate of a sandy loam under continuous water sprinkling at a rate in excess of intake with a series of 4 surface conditions (Ferguson, 1994: 191). 12

13 Infiltration Trench & Soakaway Manhole 1. Grass or Other Planting 2. Finish Grade 3. Growing Medium Backfill mm Dia PVC DR28 Perforated Pipe 5. Light Non-woven Polyester Geotextile c/w Min. 400mm Laps 6. 50mm Drain Rock 7. Maximum Groundwater Elevation 8. Non-polluted Drainage From Building or Terrace 9. Alternate Surface Route - With Splash Pad and Swale to CB 10. CB Lid / Access Hatch for Cleanout, Inspection and Inflow / Overflow from Sump 11. Solid Pipe c/w Inlet Tee 12. Observation Well (Optional) 13. Provide pipe elbows to have outlet pipe invert at top of infiltration pipe 14. PVC Solid Pipe 15. Discharge to Storm Drainage System. Ensure Drainage Does Not Impact Neighbouring Uses. Direct Discharge to Road ROW if Necessary 16. Infiltration Trench with Level Bottom 17. Catch Basin 18. Building Footing Drain (Not Connected to Infiltration Facility) 19. Building mm Dia Drain Hole On-Lot Source Controls Silver Ridge, Maple Ridge, BC 13

14 On-Lot Source Controls Infiltration Swale System Partial Infiltration Swale with Reservoir and Subdrain 1. Weir Keyed into Swale Side Slope 2. Growing Medium (300mm Min.) 3. Sand 4. Existing Scarified Subsoil 5. Perforated Underdrain (150mm Dia. Min.) 6. Drain Rock Reservoir (300mm Min.) 7. Geotextile Along All Sides of Reservoir 8. Trench Dams at All Utility Crossing 14

15 Infiltration Swale System Conveyance, Infiltration, Open Space/Greenway, Ecology Infiltration Swale System 15

16 Infiltration Swales Silver Ridge, Maple Ridge, BC Infiltration Swales Silver Ridge, Maple Ridge, BC 16

17 Infiltration Rain Garden Full Infiltration Rain Garden with Reservoir 1. Tree, Shrub and Groundcover Plantings 2. Growing Medium Minimum 450mm Depth 3. Drain Rock Reservoir 4. Flat Subsoil - scarified 5. Perforated Drain Pipe 150mm Dia. Min. 6. Geotextile Along All Sides of Drain Rock Reservoir 7. Overflow (standpipe or swale) 8. Flow Restrictor Assembly 9. Secondary Overflow Inlet at Catch Basin 10. Outflow Pipe to Storm Drain or Swale System 11. Trench Dams at All Utility Crossings Stormwater Parks Neighbourhood amenity Increased ecological function Valuable visual amenity 17

18 Pervious Paving Pervious concrete, Seattle. Pervious cobble, Netherlands. Pervious Paving Partial Infiltration Pervious Paving 1. Permeable Pavers (Min. 80mm thickness) 2. Aggregate Bedding Course - not sand (50mm depth) 3. Open Graded Base (depth varies by design application) 4. Open Graded Sub-base (depth varies by design application) 5. Subsoil level and scarified 6. Geotextile on All Sides of Reservoir 7. Optional Reinforcing Grid for Heavy Loads 8. Perforated Drain Pipe 150mm Dia. Min. 9. Geotextile Adhered to Drain at Opening 10. Flow Restrictor Assembly 11. Secondary Overflow Inlet at Catch Basin 12. Outlet Pipe to Storm Drain or Swale System. Locate Crown of Pipe Below Open Graded Base (no. 3) to Prevent Heaving During Freeze/Thaw Cycle 13. Trench Dams at All Utility Crossings 18

19 Skytrain Stormwater Concept Evergreen Line Stormwater Concept, Burnaby/Coquitlam, BC Stormwater Surface Ponds Detention Ponds / Constructed Wetlands (UniverCity at SFU) 19

20 Stormwater Surface Ponds Constructed Wetlands - UniverCity at SFU Stormwater Surface Ponds Constructed Wetlands - UniverCity at SFU 20

21 Large and Small Scale contributions Rain Garden in BC during wet weather Putting it all together 21

22 Cities as Ecosystems Thank You SOURCE CONTROLS: Think watershed scale, act at the site scale Questions? 22