Low Impact Development Guidelines
What is it?
Low Impact Development (LID) is a municipal stormwater management strategy that seeks to mitigate the impacts of increased runoff and stormwater pollution resulting from land development by managing runoff as close to its source as possible, emphasizing natural features and processes, and working to replicate the pre-development hydrologic regime.
LID can be integrated into municipal runoff volume control, planning processes, bylaws, servicing standards, design and construction specifications, and other relevant standards and guidelines.
How can municipalities use it?
Different municipalities will use LID differently: some to improve water quality (e.g., recreational lake communities experiencing harmful algal blooms), others to minimize runoff amounts to protect downstream infrastructure and the stability of streams, yet others to supplement the capacity of grey infrastructure. LID stresses that nature-based solutions take priority over enhancements to end-of-pipe facilities.
LID targets and objectives should be determined in watershed management plans and/or Municipal Development Plans. Targets and objectives can then be explicitly recognized and referenced in the development of the municipal Stormwater Management Plan or the Master Drainage Plan associated with an Area Structure Plan.
What are the advantages?
The advantages of Low Impact Development include:
Puts value on natural infrastructure assets for stormwater management
Incorporates stormwater management functionality into the existing landscape
Improves the quality of the source water that we use for our drinking water, thus simplifying and reducing the costs of potable water treatment processes.
Reduced lifecycle and regenerative costs (compared to conventional infrastructure) for the municipality and its citizens
Ability to continue land development without exacerbating downstream flooding
Supports “stacked” or corollary benefits such as carbon sequestration, urban heat island reduction, pollinator habitat, habitat connectivity, and increased well-being from green surroundings
What should you watch out for?
No tool is a silver bullet. The following should be considered when implementing Low Impact Development:
Land development proponents may misrepresent pre-development and post-development runoff conditions in order to reduce required measures
Stormwater is dirty, and there is a lot of it, so it cannot just be funnelled into the natural environment without significant attention to matching pre-development conditions
Some valuable LID / natural infrastructure assets may be on private land
Existing bylaws may conflict with LID approaches and tools (e.g., bylaws against long grass may conflict with establishing native prairie-type landscapes)
Water volume and rate control are different, and LID approaches and practices must treat them as such
Uncontrolled discharges of stormwater may have significant impacts on existing, natural wetlands
While the literature may suggest a focus on infiltration, the predominant pre-development water cycle mechanism in large parts of Alberta was evapotranspiration, so practices should therefore be sized and geared towards storage and evapotranspiration
How can it help maintain natural infrastructure?
Low Impact Development includes a range of approaches, principles, and practices, many of which support maintenance of the natural infrastructure system, including:
Conservation of features such as wetlands, natural drainage courses, vegetation, and soil, all the way down to the lot level (e.g., a single tree on a property)
Planning to slow down and lessen amounts of runoff by, e.g., decreasing amounts of imperviousness (narrower roads and sidewalks, fused-grid layouts) and reducing slopes (lot grading at max 2%)
Pollution prevention and other non-structural management practices such as bylaws regarding picking up after pets, washing cars at car washes, and only allowing water (or ‘non-deleterious substances’) down the drain
Practices to achieve effective erosion and sediment control and soil management during construction in order to prevent soil degradation and loss as well as nutrient-laden sediment mobilization by air and water
Use of green conveyances such as vegetated swales, infiltration trenches, bioswales, and stream daylighting
Our thanks to the Alberta Low Impact Development Partnership for undertaking the background research on this tool!
Resources
Alberta Low Impact Development Partnership (ALIDP) – Non-profit society with a mission to equip Albertans to create vibrant, ecologically functional landscapes within the built environment, through comprehensive stormwater management. The partnership works across the gamut from public engagement to policy development, technical training, research, education, outreach, and on-the-ground demonstration.
ALIDP Videos
Street2Stream – A half-day introductory presentation in partnership with Cows and Fish that makes the case for LID and ties upland actions to riparian outcomes. Explains LID tools and gives local examples. Can be customized to other durations and for specific audiences.
City of Edmonton Low Impact Development Construction, Inspection and Maintenance Guide –City of Edmonton document providing guidelines for contracting and maintaining five types of LID features including bioretention, bioswale, box planter, naturalized drainage way, and permeable pavement.
City of Edmonton: Naturalization –The City of Edmonton has a long history working to naturalize its rights-of-way.
Economic Instruments to Facilitate Stormwater Management on Private Property – created by the Sustainable Technologies Evaluation Program (STEP), a partnership between several conservation groups in southern Ontario, this white paper explores the mechanisms available to incent installation of Low Impact Development (LID) technologies, with particular focus on private commercial properties.
City of Calgary: Low Impact Development – This website houses a variety of resources for LID, including design and construction guidance for geotechnical and hydrogeological considerations, bioretention and bioswales, green roofs, and permeable pavement. It also includes information on rainwater harvesting, and source control practices.
City of Calgary Stormwater Management & Design Manual –City of Calgary document is a comprehensive design manual for effective, reliable, and economically affordable systems. This document includes information on LID approaches.
Standards and Guidelines for Municipal Waterworks, Wastewater and Storm Drainage Systems: Part 5 Stormwater Management Guidelines - In this document, the Government of Alberta outlines several LID tools.
Did we miss something?
If you know of a resource that should be on this list - or your municipality has a sample or case that should be here, please let us know!