Introduction to Low Impact Development Dr Kathy Chaston Coral & Coastal Management Specialist NOAA Office of Ocean & Coastal Resource Management
http://hawaii.gov/dbedt/czm/resource/publication.php
A Comprehensive Approach Better Site Planning Large Stormwater Management Practices Better Site Design Low Impact Development Practices Receiving Waters
Not Address Where Development Occurs Site design Principles Address How Development Occurs
Evolved over the past 50 years large lot Clearing and grading of whole site Wide streets and cul de sacs Lots of impervious cover Removal of native soils Enclosed drainage systems for stormwater conveyance Reliance on hole in the ground detention basins Limited clearing Efficient use of impervious cover Taking advantage of natural hydrology Non structural approach to stormwater Conservation of natural areas
What s in it for me? Improved water quality, reduced water quantity, increased recharge; Reduced construction costs & long term operation and maintenance costs; Increased property values; More open space for recreation; More pedestrian friendly neighborhoods; Protection of sensitive forests, wetlands, and habitats; and Increased market diversity
LID Planning Process: 1. Avoid the Impacts Preserve natural features and use conservation design techniques 2. Reduce the Impacts Reduce and disconnect impervious cover 3. Manage the Impacts Utilize natural features and natural lowimpact techniques to manage stormwater
LID is used to reduce the footprint of development and thereby reduce impacts to sensitive water resources Treats water as a resource
LID Planning Process: Avoid the Impacts Preservation of Undisturbed Areas Preservation of Buffers Reduction of Clearing and Grading Locating Sites in Less Sensitive Areas Open Space Design
Preserve Natural & Sensitive Areas
Preserve Vegetated Buffers
Conserve trees
Limit clearing and grading
Large Impact Area Small Impact Area Roads on ridge lines or upland areas Houses located on brow of ridge Vegetated drainage swales Natural drainageways preserved Undisturbed vegetation on slopes
Open space design
LID Planning Process: Reduction of Impervious Cover Roadway Reduction Sidewalk Reduction Driveway Reduction Cul de Sac Reduction Building Footprint Reduction Parking Reduction
Reduce size of roads and sidewalks
26 PAVE WIDTH 10 DRAINAGE SWALE 4 SIDEWALK 3 UTILITY 60 RIGHT OF WAY 18 PAVE WIDTH 6 DRAINAGE SWALE 3 UTILITY 36 RIGHT OF WAY
Reduce Driveways
Minimize Cul de Sacs
Reduce Parking Lot Imperviousness Set appropriate parking ratios Provide compact car spaces Minimize stall dimensions Incorporate efficient parking lanes Use pervious material in spillover areas
http://www.invisiblestructures.com
LID Planning Process Manage the Impacts Utilize natural features and LID techniques to manage stormwater Don t discharge untreated stormwater Integrate stormwater into landscaping Use combo of LID and large scale practice
A Comprehensive Approach Better Site Planning Large Stormwater Management Practices Better Site Design Low Impact Development Practices Receiving Waters
LID Stormwater Management Approach Managing runoff using small scale, distributed, onsite practices Mimic natural hydrology Designs that infiltrate, filter, store, evaporate, and detain water close to it s source Use larger practices, if necessary, to manage runoff from larger storms
What s Good About Distributed Practices? Allows infiltration across broader landscape More use of vegetation for stormwater treatment Reserves basins for flood control/larger storms Can be aesthetically pleasing Can be good public outreach tools Replicates pre development hydrology
BUT... Ponds are prevalent because they can be designed with capacity to meet stormwater criteria in local codes LID More complicated design/plan review/construction More areas to maintain Requires higher level of program sophistication
Considerations for Stormwater Management Implementation Rainfall Amounts Soils Depth to groundwater Topography (slope, available head) Drainage area Land use and density Design objectives (recharge, water quality vs. quantity, target pollutants) Community/environmental factors Maintenance PRETREATMENT
Vegetated Channels
Rain Gardens / Bioretention
Materials Stone/Gravel Underdrain Pipe Soil/Sand Mix Mulch/Ground Cover Plants
Optional Underdrain System
Infiltration
Permeable Pavement
Typical Materials Complete infiltration or use of underdrains (soil depending) Fill and Bedding Material Base course layer supports traffic loads and retains a portion of the infiltrated rainfall Source: Hunt and Collins, 2008
Materials Pavement Surface Sand or Pea Gravel for Bedding Stone/Gravel storage layer Underdrain Pipe (some applications)
Reduce Rooftop Runoff: Rainwater harvesting
Green Rooftops
Downspout Disconnection
Managing Rooftop Runoff GOOD Not GOOD
Roof scuppers drain to biofiltration channel Sanitation District No. 1 of Northern Kentucky
Managing Parking Lot Runoff
Managing Parking Lot Runoff Not so good GOOD
Managing Street Runoff
Managing Street Runoff Not so good? Worse GOOD
A Comprehensive Approach Better Site Planning Large Stormwater Management Practices Better Site Design Low Impact Development Practices Receiving Waters
Residential Development Example Conventional Low Impact Development
Commercial Development Example Conventional Low Impact Development
Individual Residential Lot Example
Take Home Points Need to use a combination of site planning, on site and storage stormwater practices to manage runoff Poor design=more stormwater to manage Need to implement designs to mimic predevelopment hydrology Need to adapt LID practices to Hawaii topography and rainfall
LID References: Arendt, Randall. 1996. Conservation Design for Subdivisions: A Practical Guide to Creating Open Space Networks. American Planning Association. Chicago, IL. Available from the American Planning Association at www.planning.org Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Available from www.cwp.org Low Impact Development (LID) Center website: http://www.lowimpactdevelopment.org/ Massachusetts Executive Office of Environmental Affairs (EOEA). 2005. Smart Growth Toolkit. Boston, MA. Available from http://www.mass.gov/envir/smart_growth_toolkit/
More Information? Kathy Chaston Kathy.Chaston@noaa.gov Center for Watershed Protection www.cwp.org Horsley Witten Group www.horsleywitten.com