A new tool for stormwater management planning and design practices

A new, Low Impact Development Treatment Train Tool helps developers, consultants, municipalities and landowners understand and implement more sustainable stormwater management planning and design practices in their watersheds.

How has urbanization impacted stormwater management?

Traditional stormwater practices were designed to convey water as quickly as possible to the outlet, either through natural or built water courses, to prevent flooding especially during larger storms. However, urbanization intensified upstream quickly and widely with increased impervious surfaces and sources of pollution, to a point where the additional water volume and pollution load could not be managed by the receiving courses. The increased stormwater load can degrade the natural landscapes it flows through, damage built infrastructure and even endanger lives. Stormwater has to be slowed down, reduced and treated before allowing it to be conveyed downstream.

The aim of sustainable stormwater practices also referred to as Green Infrastructure (GI), Low Impact Development (LID) , or Best Management Practices (BMPs) is to treat stormwater as close to the source as possible, either by delaying or reducing the stormwater runoff and by removing pollutants from it before conveying it downstream. Common goals for these practices include having post-development infiltration volumes and peak flow rates match pre-development values or creating the capacity to retain the runoff from a 12.5 – 25 mm event.

Low Impact Development, bioswale, rain garden
A bioswale treats runoff from paved areas by using the natural properties of soil and vegetation to remove contaminants and allow stormwater to infiltrate the ground.

LID comprises a set of site design strategies that minimize runoff by means of distributed, small scale structural practices that mimic natural or predevelopment hydrology through the processes of infiltration, evapotranspiration, harvesting, filtration and detention of stormwater. Usually, because one structure cannot treat the volume or the variety of pollutants for the entire drainage area, the stormwater is conveyed through a treatment train of a number of LIDs. These practices can effectively remove nutrients, pathogens and metals from runoff, while reducing the volume and intensity of stormwater flows.

The purpose of the LID Treatment Train Tool (LID TTT) is to analyze whether sustainable stormwater management goals can be achieved through the implementation of LIDs. The tool is used to compare hydrology and pollutant loading for the pre- and post-development (with LIDs) scenarios using annual and event based simulations.

What is the Low Impact Development Treatment Train Tool?

The LID TTT, which is free for users, was developed by Sustainable Technologies Evaluation Program (STEP Water), a partnership between Lake Simcoe Region Conservation Authority (LSRCA), Credit Valley Conservation (CVC) and Toronto and Region Conservation Authority (TRCA). The goal was to streamline the planning and approval process by selecting and organizing the results of the model simulations and comparisons in a way that is clear and aligned with Ministry of the Environment and Climate Change (MOECC) guidelines, thus eliminating any additional downloads or additional computations.

The LID TTT conceived as a preliminary design tool can be used for designing and running a scenario very quickly, perhaps within a time frame of a collaborative design charrette. To support this, the tool includes a number of default settings, which can be altered depending on a user’s experience and monitoring studies. Also built into the tool are annual rainfall series, design storms time series, and temperature time series for quicker model setup. The tool also provides preliminary water budget analysis (i.e. surface ET, surface runoff, infiltration to soil) and pollutant load removal estimates that can be compared side by side for pre- and post-development scenarios.

The tool is built upon the widely used and accepted open source EPA SWMM5 model. While there are a number of models that do this already, this particular tool provides a very user-friendly interface for novice modelers. Because it is built upon the SWMM 5 engine, a preliminary design can be exported directly into SWMM 5 for detailed design. Support for users is available through the STEP website where they can access FAQs and contact technical advisors.

Who would benefit from using the Low Impact Development Treatment Train Tool?

The LID TTT will assist stormwater developers, designers, water resource engineers, municipal staff, landscape architects, and planners understand and implement more sustainable stormwater management planning and design practices in their watersheds.

Users can download the LID TTT at https://sustainabletechnologies.ca/low-impact-development-treatment-train-tool/. Users will also find upcoming training for the tool offered through on-line webinars or in class workshops in the coming months.


Yuestas David is a Technical Analyst at Toronto and Region Conservation Authority (TRCA) within the Sustainable Technologies Evaluation Program group. He engages in research and development, web development, data analysis, technical report writing and the effective communication of findings from various projects and initiatives related to urban stormwater management. He graduated with a Master’s of Science from the Geography program at York University with a focus on hydrological modeling.