A new tool for stormwater management planning and design practices

A new tool for stormwater management planning and design practices

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 infiltrationevapotranspiration, 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.

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