Screening LID options

Process for selecting an individual or suite of LID Options

Process Diagram for Screening LID Options

The guidance found on this page is not intended be prohibitive of LID options, but rather to help reduce the number of LID options in the preliminary phases of design and alert the designer to LID opportunities unique to the site being assessed. When going through the process of screening LID options, it is important to have a larger contextual understanding of Integrated water management, Site design strategies, Siting and layout of development, and Link title.

Site Conditions

Complete definition of pre-development site conditions is essential prior to screening of potential stormwater BMPs. The designer should prepare maps describing site conditions to ensure that all environmental features and functions that need consideration in accordance with provincial, municipal and conservation authority development regulations are identified. This includes watercourses and small drainage features, floodplains, important recharge areas, steep slopes, wetlands, natural heritage conservation areas and significant wildlife habitats. In addition, information regarding native soil types, infiltration capacity and depth to water table must be determined.

In retrofit scenarios, site conditions will vary and can be explicit with land use type such as road right of ways, parks, residential, industrial, commercial and/or institutional should be noted.

For additional information on site conditions to note for:

• Road right of way retrofits, see Site Conditions Road Right of Ways
• Public lands including parks, churches, or schools, see Public Lands Site Conditions
• Commercial, industrial and multi-residential, see Site Conditions Commercial, Industrial, and Multi-Residential
• Residential, see Site Conditions Residential

Define Design Criteria

A detailed description of the design criteria that need to be defined is provided in the respective CVC and TRCA Stormwater Management Criteria documents. If outside jurisdictional boundaries, criteria developed should have requirements to:

• Preserve groundwater and baseflow characteristics;
• Prevent undesirable and costly geomorphic changes in the watercourse;
• Prevent any increases in flood risk potential;
• Protect water quality; and ultimately,
• Maintain an appropriate diversity of aquatic life and opportunities for human uses

The design criteria required to protect, enhance or restore the environmental resources can be grouped under the following five categories.

• Flood Protection;
• Water Quality;
• Erosion Control;
• Recharge; and
• Natural Heritage Systems or green infrastructure

Screen Potential LID Options

Site Constraints

A number of factors need to be considered when screening the suitability of a given location within a development site for application of stormwater BMPs. LID Site Criteria and Constraints summarizes site constraints associated with some general types of structural LID practices for stormwater management that should be considered. Further information regarding constraints to the design of various end-of-pipe BMPs can be found in the Ontario Ministry of the Environment Stormwater Management Planning and Design Manual (2003). The use of LID BMPs should be considered first to meet the design criteria before the use of end-of-pipe BMPs.

If working in a retrofit scenarios, land use type in particular will have various constraints to work with. Road ROWs, industrial, commercial, institutional, residential, and park lands all have unique site constraints and corresponding LID opportunities. To help understand these unique land type constraint and potential LID options, see

• LID Opportunities and Road Types

• LID Opportunities in Residential and Multi-Residential Types

• LID Opportunities in Industrial & Commercial Types

• LID Opportunities in Institutional Types

• LID Opportunities in Park Lands

Performance Requirements

Resources on LID performance studies are widely available. Performance of LID within Ontario can be found on the Sustainable Technologies Evaluation Program and Credit Valley Conservation's LID Monitoring program. To garner a global perspective of LID performance across various geographical regions, check out the International Stormwater BMP Database, performance data can be downloaded or uploaded and statistical analysis tools are provided.

Operations and Maintenance Requirements

LID Inspection and Maintenance Guide is intended to assist municipalities and industrial/commercial/institutional (ICI) property managers with developing their capacity to integrate LID BMPs into their stormwater infrastructure programs. Part 1 of the document provides guidance on designing an effective LID BMP inspection and maintenance program, based on experiences and advice from leading jurisdictions in the United States, adapted to an Ontario context. Part 2 of the document establishes standard cold climate protocols for inspection, testing and maintenance of seven types of structural LID BMPs.

Life Cycle Costing Requirements

The capital and life cycle costs of seven Low Impact Development (LID) practices and seventeen design scenarios were evaluated based on a detailed assessment of input costs, maintenance requirements, rehabilitation costs and practice designs relevant to Canadian climates.The LID Life Cycle Costing Tool

Selection of Suite of LIDs

LID Treatment Train Tool

In order to assess if the selected suite of BMPs effectively meet the design criteria either computer models or simple spreadsheet models should be used. Model selection will be based on the size and type of development. A wide range of simple to complex computer models such as Visual OTTHYMO, SWMM, SWMMHYNO, HSP-F andQUALHYMO are available.

Recently, the Low Impact Development Treatment Train Tool (LID TTT) has been developed by Lake Simcoe Region Conservation Authority (LSRCA), Credit Valley Conservation (CVC) and Toronto and Region Conservation Authority (TRCA) as a tool to help developers, consultants, municipalities and landowners understand and implement more sustainable stormwater management planning and design practices in their watersheds. The purpose of the tool is to analyze annual and event based runoff volumes and pollutant load removal by the use of Best Management Practices (BMP)’s and Low Impact Development (LID) techniques.

The LID TTT provides preliminary water budget analysis (i.e. surface ET, surface runoff, infiltration to soil) and pollutant load removal estimates for pre- and post-development scenarios. The tool is built upon the open source EPA SWMM5 model providing a user-friendly interface for novice modelers and cross-compatibility with SWMM5 for further model development. To download the beta version, please check out the LID Treatment Train Tool

Assess Effectiveness

Once the suite of best management practices have been selected and the models have been run, a comparison of the results and the environmental design criteria can be made. An iterative approach, which involves adjusting the size or adding/deleting BMPs should be used until the environmental design criteria are met. The LID Treatment Train Tool can help with adjusting the size of the features to see if criteria are met. Once met, the project can then proceed to the detailed design stage.

Low 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.

refers to the characteristics and functions of a system prior to urban development.

The 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.

The natural ground material characteristic of or existing by virtue of geographic origin.

The upper surface of the zone of saturation, except where the surface is formed by an impermeable body.

Subsurface water level which is defined by the level below which all the spaces in the soil are filled with water; The entire region below the water table is called the saturated zone.

Credit Valley Conservation

Toronto and Region Conservation Authority

(a) A natural well-defined channel produced wholly or in part by a definite flow of water and through which water flows continuously or intermittently. Also, a ditch, canal, aqueduct, or other artificial channel for the conveyance of water to or away from a given place, as for the draining of a swamp.

(b) A stream or current of water. Legally, a natural stream arising in a given drainage basin but not wholly dependent for its flow on surface drainage in its immediate area, flowing in a channel with a well-defined bed between visible banks or through a definite depression (as a ravine or swamp) in the surrounding land, having a definite and permanent periodic supply of water (the stream may be intermittent), and usually, but not necessarily having a perceptible current in a particular direction and discharging at affixed point into another body of water.

(c) A legal right permitting the use of a flow of a stream (especially of one flowing through one’s land) or the receipt of water discharged upon land belonging to another.

The 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.

Natural vegetation and vegetative technologies in urban settings such as: urban forests; green roofs; green walls; green spaces; rain gardens; bioswales; community gardens; natural and engineered wetlands and stormwater management ponds; and porous pavement systems. These systems are designed to provide multiple benefits, such as moderate temperatures, clean air and water, and improve aesthetics.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

Best management practice. State 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.

Low impact development is a stormwater management and land development strategy applied at the parcel and subdivision scale that emphasizes conservation and use of on-site natural features integrated with engineered, small scale hydrologic controls to more closely mimic pre-development hydrologic functions.

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.

Lake Simcoe Region Conservation Authority

The portion of water precipitated onto a catchment area, which then 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.

The total mass of a pollutant entering a waterbody over a defined time period.

State 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 mathematical expression of the water balance.

Evapotranspiation

State 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.