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Lid Presentation

  1. 1. The Urban Watershed and Low Impact Design Materials courtesy of the SFPUC Urban Permaculture InstituteUrban Permaculture Institute
  2. 2. W h a t i s L o w I m p a c t D e s i g n ?  LID is a stormwater management approach that aims to re-create and mimic these pre-development hydrologic processes by increasing retention, detention, infiltration, and treatment of stormwater runoff at its source.  LID is a distinct management strategy that emphasizes on-site source control and multi-functional design, rather than conventional pipes and gutters.  Whereas BMPs are the individual, discrete water quality controls, LID is a comprehensive, watershed- or catchment-based approach.  These decentralized, smallscale stormwater controls allow greater adaptability to changing environmental and economic conditions than centralized systems.
  3. 3. Eco Roofs  Green roofs, or eco-roofs, are roofs that are entirely or partially covered with vegetation and soils.  Eco-roofs have been popular in Europe for decades and have grown in popularity in the U.S. Recently as they provide multiple environmental benefits.  Eco-roofs improve water quality by filtering contaminants as the runoff flows through the growing medium or through direct plant uptake.  Studies have shown reduced concentrations of suspended solids, copper, zinc, and PAHs (polycyclic aromatic hydrocarbons) from eco- roof runoff.
  4. 4. D e s i g n D e t a i l s  An intensive eco-roof may consist of shrubs and small trees planted in deep soil (more than 6 inches) arranged with walking paths and seating areas and often provide access for people.  In contrast, an extensive eco-roof includes shallow layers (less than 6 inches) of low-growing vegetation and is more appropriate for roofs with structural limitations.  Both categories of eco-roofs include engineered soils as a growing medium, subsurface drainage piping, and a waterproof membrane to protect the roof structure.
  5. 5. Benefits  Provides insulation and can lower cooling costs for the building  Extends the life of the roof – a green roof can last twice as long as a conventional roof, saving replacement costs and materials  Provides noise reduction  Reduces the urban heat island effect  Lowers the temperature of stormwater runoff, which maintains cool stream and lake temperatures for fish and other aquatic life  Creates habitat and increases biodiversity in the city  Provides aesthetic and recreational amenities
  6. 6. Limitations  Poor design or installation can lead to potential leakage and/or roof failure  Limited to roof slopes less than 20 degrees (40 percent or a 5 in 12 pitch)  Requires additional structural support to bear the added weight  Potentially increased seismic hazards with increased roof weight  Long payback time for installation costs based on energy savings  May attract unwanted wildlife  Inadequate drainage can result in mosquito breeding  Irrigation may be necessary to establish plants and maintain them during extended dry periods  Vegetation requires maintenance and can look overgrown or weedy, seasonally it can appear dead
  7. 7. Downspout Disconnect  Downspout disconnection, also called roof drain diversion, involves diverting rooftop drainage directly into infiltration, detention, or storage facilities instead of into the sewer.  Rainwater can be harvested from most types of rooftops.  In areas where site conditions allow infiltration, roof drainage can be conveyed to drainless bioretention planters, dry wells, or can be simply dispersed onto a rain garden, lawn, or landscaped area  On sites that are not amenable to infi ltration, roof drains can be routed into cisterns which are available in a range of materials, sizes, and models.
  8. 8. Benefits  Reduces runoff volume and attenuates peak flows  May decrease water usage through lowered irrigation requirements  Low installation costs  Low maintenance requirements  Large variety of implementation locations and scales
  9. 9. Limitations  Pre-fi ltration (such as a first-flush diverter) is required if water is to be stored  Added complexity for buildings with internally plumbed stormwater drains  Secondary system is required to deal with water after it leaves the downspout, such as a cistern or a rain garden
  10. 10. Retrofit where appropriate
  11. 11. Cisterns  Cisterns are a traditional technology employed in arid climates to capture and store rainwater.  Cisterns reduce the stormwater volume by capturing rainwater for non- potable uses, such as irrigation or fl ushing toilets.  Suitable for a single house or an entire neighborhood, cisterns range in size and may be placed above ground or underground.
  12. 12. C a s e S t u d y : C a m b r i a , C A Cambia Elementary School captures and stores runoff water from the entire school site in a cistern located underneath athletic fields and uses the stored water to irrigate the fields year round. All of the stormwater on the 12 acre campus is captured and stored in large pipes that are located under 130,000 square feet of new athletic fields. Up to 2 million gallons of water can be stored.
  13. 13. Benefits  Reduces runoff volume and attenuates peak flows  May decrease water usage if retained for irrigation purposes or toilet flushing  Low installation costs  Low maintenance requirements (for above ground cisterns)  Low space requirements (for underground cisterns)  Good for sites where infiltration is not an option
  14. 14. Limitations  Poor design, sizing, and siting can lead to potential leakage and/or failure  Storage capacity is limited  Provides no water quality improvements  Lower aesthetic appeal (for above ground cisterns)  Water reuse options limited to non-potable uses  Requires infrastructure (pumps or valves) to use the stored water  Inadequate maintenance can result in mosquito breeding and/or algae production
  15. 15. Rain Gardens  Rain gardens are stormwater facilities integrated into depressed landscape areas.  They are designed to capture and infiltrate stormwater runoff.  Rain gardens include water-tolerant plants in permeable soils with high organic contents that absorb stormwater and transpire it back into the atmosphere.  Rain gardens are a subset of bioretention planters except that they do not typically include engineered soils or an under-drain connection.  Plant species can be selected to stack functions and provide yields.
  16. 16. Benefits  Reduces runoff volume and attenuates peak flows  Improves water quality  Improves air quality  Improves urban hydrology and facilitates groundwater recharge  Low installation costs, low maintenance requirements, low space requirements  Creates habitat and increases biodiversity in the city  Provides aesthetic amenity  Easily customizable
  17. 17. Limitations  Depth to bedrock must be over 10 feet for infiltration based systems  Limited to slopes less than 5 percent, slopes greater than 5 percent require check dams  Seasonal fluctuation in water quality benefits based on the plants’ ability to filter pollutants  Vegetation requires maintenance and can look overgrown or weedy, seasonally it may appear dead  Site conditions must be conducive to partial or full infiltration and the growing of vegetationor an underdrain is needed  10 foot minimum separation from groundwater is required to allow for infiltration,unless the Regional Water Quality Control Board approves otherwise  Non-underdrained systems must have minimum soil infiltration rates
  18. 18. Typical Rain Garden
  19. 19. Bioretention Planters  Bioretention is the use of plants, engineered soils, and a rock sub-base to slow, store, and remove pollutants from stormwater runoff.  Bioretention planters improve stormwater quality, reduce overall volumes, and delay and reduce stormwater runoff peak flows.  Bioretention planters can vary in size from small, vegetated swales to multi-acre parks; however, there are limits to the size of the drainage area that can be handled.  System designs can be adapted to a variety of physical conditions including parking lots, roadway median strips and right-of-ways, parks, residential yards, and other landscaped areas and can also be included in the retrofits of existing sites.
  20. 20. Benefits  Reduces runoff volume and attenuates peak flows  Improves water quality  Improves air quality  Improves urban hydrology and facilitates groundwater recharge  Lowers the temperature of stormwater runoff, which maintains cool stream temperatures for fish and other aquatic life  Creates habitat and increases biodiversity in the city  Provides aesthetic amenity  Reduces the heat island effect
  21. 21. Limitations  Depth to bedrock must be over 10 feet for infiltration based systems  Limited to slopes less than 5 percent, slopes greater than 5 percent require check dams  Seasonal fluctuation in water quality benefits based on the plants’ ability to filter pollutants  Vegetation requires maintenance and can look overgrown or weedy, seasonally it may appear dead  Site conditions must be conducive to partial or full infiltration and the growing of vegetationor an underdrain is needed  10 foot minimum separation from groundwater is required to allow for infiltration,unless the Regional Water Quality Control Board approves otherwise  Non-underdrained systems must have minimum soil infiltration rates
  22. 22. Street-side bioretention planter based on Portland’s Green Streets
  23. 23. Detention Basins  Detention basins are temporary holding areas for stormwater that store peak flows and slowly release them, lessening the demand on treatment facilities during storm events and preventing flooding.  Generally, detention basins are designed to fi ll and empty within 24 to 48 hours of a storm event and therefore could reduce peak flows and combined sewer overflows.  If designed with vegetation, basins can also create habitat and clean the air whereas underground basins do not.  Surface detention basins require relatively flat slopes.
  24. 24. Four Basic Types of Detention Basins Traditional dry detention basins simply store water and gradually release it into the system. Dry detention basins do not provide water quality benefits, as they only detain stormwater for a short period of time. Maintenance requirements are limited to periodic removal of sediment and maintenance of vegetation. Dry detention basins are good solutions for areas with poorly draining soils, high liquefaction rates during earthquakes, or a high groundwater table, which limit infiltration.
  25. 25. Four Basic Types of Detention Basins Extended dry detention basins are designed to hold the first flush of stormwater for a minimum of 24 hours. Extended dry detention basins have a greater water quality benefit than traditional detention basins because the extended hold time allows the sediment particles to settle to the bottom of the pond. Collected sediments must be periodically removed from the basin to avoid re-suspension.
  26. 26. Four Basic Types of Detention Basins Underground detention basins are well suited to dense urban locations where land costs make surface options unfeasible. Underground detention basins work best if partnered with an ‘upstream’ BMP that provides water quality benefi ts, like bioretention planters, if water is not returned to the combined sewer overflow. Underground detention basins need to be on a slight slope to facilitate drainage but should not be placed on steep slopes because of the threat of erosion. They can be placed under a roadway, parking lot, or open space and are easy to incorporate into other right-of-way retrofits.
  27. 27. Four Basic Types of Detention Basins Multi-purpose detention basins are detention basins that have been paired with additional uses such as large play areas, dog parks, athletic fields or other public spaces. Generally detention basins are only filled with water during storm events and can act as open spaces during dry weather.

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