Evolution of SWM

From LID SWM Planning and Design Guide
Jump to: navigation, search

In the mid 1970s, attempts to control runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. flow rates from urban developments were initiated. By the late 1980s, water quality became an additional focus and in the late 1990s, approaches to mitigate accelerated stream channelA natural waterway, formed by fluvial processes, that conveys running water. erosion were introduced. Lot levelThe treatment of urban runoff as close to the source area as possible through application of small scale stormwater management practices on individual properties that are linked to downstream conveyance and end-of-pipe practices. stormwater management approaches have been advocated in Ontario since 1995 (OMMAH, 1995), but widespread application has yet to occur. Today, with improvements in our understanding of watershed systems and the potential impacts urbanizationThe changing of land cover and land uses from rural to urban; the growth of urban settlements. can have on aquatic ecosystems, stormwater management addresses a broad suite of issues including fluvial geomorphologyThe study of the processes responsible for the shape and form, or morphology, of watercourses; describes the processes whereby sediment (e.g., silt, sand, gravel) and water are transported from the headwaters of a watershed to its mouth. (stream channelA natural waterway, formed by fluvial processes, that conveys running water. forming processes), groundwater resources and the protection of aquatic and terrestrial habitats.

Municipalities, with the support of conservation authorities, review stormwater management facilities and plans designed to address this multitude of concerns. This has led to an increasing complexity in stormwater management planning and design including:

  • increasingly complex stormwater management facilities and best management practicesState of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls.;
  • the need to involve more inter-disciplinary expertise in studies to define environmental opportunities and constraints;
  • expanding requirements for multi-purpose stormwater management facilities; and,
  • increased emphasis on the treatment trainStormwater management following the hierarchical approach: Source Control measures, Conveyance Control measure and End of Pipe treatment to achieve the water quality and water balance target for lot level development of the preferred strategy.A combination of lot level, conveyance, and end-of-pipe stormwater management practices. approach and use of multiple types of controls to address environmental issues.

CVCCredit Valley Conservation and TRCAToronto Region Conservation Authority have been extensively involved in integrated watershedThe drainage area of a river.An area of land that drains into a river or a lake. The boundary of a watershed is based on the elevation (natural contours) of a landscape.-wide environmental monitoring for many years. The results of this monitoring have shown that the environmental health of many watersheds continue to decline as urbanizationThe changing of land cover and land uses from rural to urban; the growth of urban settlements. increases. This environmental deterioration has taken place despite widespread compliance with provincial and conservation authority requirements for stormwater management planning and facility design. Conventional stormwater management, which focuses on controlling peak flow rate and the concentration of suspended solids, has failed to address the widespread and cumulative hydrologic modifications in watersheds that increase the volume of stormwaterSurface runoff from at-grade surfaces, resulting from rain or snowmelt events., increase the runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. rate, and cause excessive erosion and degradation of stream channels. Conventional stormwater management also fails to adequately treat other pollutants of concern, such as nutrients, pathogens and metals.

This is why CVCCredit Valley Conservation and TRCAToronto Region Conservation Authority commissioned the development of the 2010 stormwater management guide, to provide guidance on the kind of cutting edge practices that are needed to protect the health of the CVCCredit Valley Conservation and TRCAToronto Region Conservation Authority watersheds. The LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. SWMStormwater Management Guide draws on published research, literature and local studies to provide planning and design guidance that reflects regional policies, practices and climate. It provides information and guidance on the following:

  • how to integrate stormwater management into the urban planning process;
  • how to design, construct and maintain a range of LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. stormwater management practices; and
  • the kinds of environmental and performance monitoring that should be carried out.

Acknowledging that it will not always be possible to maintain the predevelopment water budgetThe mathematical expression of the water balance. of a site, predicted increases in runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from land development that cannot be mitigated through stormwater infiltration practices should be minimized through practices that either evapotranspire (e.g., green roofs, bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.), or harvest runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. for non-potable uses (i.e., rainwater harvestingThe practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.). In areas where development has already taken place, LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. can be used as a retrofit practice to reduce runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. volumes, pollutant(1) Something that pollutes, especially a waste material that contaminate air, soil, or water. (2) Any solute or cause of change in physical, chemical or biological properties that render water unfit for a given use. loadings, and the overall impacts of existing developments on receiving watersWatercourses and Lake Ontario, to which Stormwater and Combined Sewer Overflows discharge.. LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. practices can include:

  • conservation site design strategies (i.e., non-structural LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. practices);
  • infiltration practices;
  • rainwater harvestingThe practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.;
  • runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. storage and evapotranspirationThe quantity of water transpired (given off). Retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively it is usually expressed in terms of depth of water per unit area during a specified period. e.g. mm/dayThe combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.;
  • runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. conveyanceMovement of water from one location to another.;
  • filtrationThe technique of removing pollutants from runoff as it infiltrates through the soil. practices; and landscaping.

Studies show that implementing LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. practices can have multiple positive environmental effects including:

  • protection of downstream resources;
  • abatement of pollution;
  • rechargeThe addition of water to ground water by natural or artificial processes.The infiltration and movement of surface water into the soil, past the vegetation root zone, to the zone of saturation or water table. of groundwaterThe water below the surface, and typically below the groundwater table.;
  • improvement of water quality;
  • improvement of habitat;
  • reduced downstream flooding and erosion(1) The wearing away of the land surface by moving water, wind, ice or other geological agents, including such processes as gravitation creep; (2) Detachment and movement of soil or rock fragments by water, wind, ice or gravity (i.e. Accelerated, geological, gully, natural, rill, sheet, splash, or impact, etc).;
  • conservation of water and energy; and
  • improved aesthetics in streams and rivers.

These combined benefits help to mitigate potential negative impacts of climate change on groundwater levels, risk of flooding and stream channelA natural waterway, formed by fluvial processes, that conveys running water. erosion(1) The wearing away of the land surface by moving water, wind, ice or other geological agents, including such processes as gravitation creep; (2) Detachment and movement of soil or rock fragments by water, wind, ice or gravity (i.e. Accelerated, geological, gully, natural, rill, sheet, splash, or impact, etc)..