Computer Simulation Makes Low Impact Development (LID) Planning Easy

Computer Simulation Makes Low Impact Development (LID) Planning Easy
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Chris Davidson

Christopher Davidson Member Name

P.Eng., Surface Water Engineer

Turning farmers’ fields into housing subdivisions and business properties in the rapidly growing Greater Toronto area creates water impacts with far-reaching implications. Rainwater that once infiltrated into the ground is now pouring quickly off impervious surfaces like roofs, roads, and parking lots. The additional runoff can cause flooding and erosion in rivers and streams, and excess sedimentation can degrade aquatic habitat. It also means that groundwater does not get replenished, which can be bad news for drinking wells and wetlands that rely on that flow.

Accordingly, provincial and municipal authorities have been promoting stormwater management that both reduces peak flows and replenishes groundwater. This awareness has resulted in new guidelines, regulation, additional stormwater fees, phosphorus development charges, and outright rejection of development plans that do not provide sufficient water management measures.

Golder, in partnership with regulators, has developed a software solution that helps property developers understand the potential impact of water management steps they are considering, and helps regulators determine if the developers’ plans are sufficient to meet the regulatory requirements. The use of current graphics technology has been instrumental in producing a tool that is easy to understand, easy to use and provides immediate feedback.

Promoting best practice in stormwater management

Golder’s Low Impact Development Treatment Train Tool (LID TTT) follows the current best practice in stormwater management.

Prior to the 1980s, stormwater management prioritized collecting runoff and routing it as quickly as possible into rivers and streams, to minimize water on streets and around buildings. However, this didn’t solve the issue—it simply pushed the problem further downstream and caused flooding and erosion along the rivers and streams.

Furthermore, since the precipitation didn’t have a chance to soak into the ground, as it had done prior to development, the groundwater didn’t get replenished. This reduction in groundwater starved wetlands of the water they needed to thrive, caused streams and rivers to run low during dry spells, and made wells run short of water.

More recently, property developers were asked to mitigate downstream flooding by storing precipitation on site through stormwater retention ponds, to slow the flow of water and settle out some of the sediment washing off the hard surfaces. These actions helped to reduce flooding and improve water quality. However, the stormwater retention ponds take up valuable development space, are ineffective at removing dissolved materials such as phosphorus, and may lead to increased surface water temperatures. The problem of lost groundwater recharge was also still not solved by the use of stormwater ponds.

To address both ongoing quality concerns and groundwater recharge, current best practice has turned to “Low Impact Development” (LID), also called “Green Infrastructure.” LID features such as green roofs, bioretention features, rain gardens, and infiltration trenches provide stormwater controls by mimicking natural processes that were present on the property before development. Features include:

The wide range of options, plus variation in the numbers and capacity of the systems selected, provides developers flexibility in how they meet the regulatory requirements for water flowing off their development.

However, understanding the strengths of the new technology can be daunting, and this has led to slow uptake of LID design in Ontario. The LID TTT was developed specifically to promote LID by helping developers navigate these options and find the best, most cost-effective solution(s) for their site.

Software that encourages best practice, with an eye on the future

The LID TTT, which Golder developed, is based on the US Environmental Protection Agency’s Storm Water Management Model open-source software (SWMM5 model). This software is designed to untangle the mysteries around LID and make it easy for property developers to understand what steps they can take – based on location, size, and function of water management systems – to meet requirements. Additionally, the transparency of the system makes it easier for regulatory agencies to determine if they can greenlight a plan or must ask for changes.

Users can take weather data for the proposed development location, upload satellite images of the area, and then overlay a plan of the proposed development. The user can then plug in possible locations and specifications for a range of stormwater management solutions – perhaps a rain garden designed to provide a given level of stormwater treatment in one location, or a filtration bed elsewhere. The model simulations provide users near-instantaneous feedback on the effects of the design options on stormwater management, infiltration, and water quality.

One of the tool’s strengths is its ability to take complex considerations and make them understandable. Having the site plan on the screen makes it easy for developers to envision the site layout, and experiment with the position, size, and configuration of water management systems to find the best possible combination that achieves the requirements.

Golder’s immediate client for this work was a group of conservation authorities, who asked for an easy-to-use software package that would help them and property developers standardize the approach for LID incorporation. Looking ahead to the next stage of development, Golder is working to strengthen the software’s ability to forecast costs for the elements included in the plans, so developers can understand how to minimize their expenses while still meeting their regulatory obligations.

To address climate change impacts, Golder’s team provided ways for users to see what might happen under the more extreme storm events that are expected over time. Users can key in values for a storm that is more severe than most, or they can use the software’s Wiki to design storms that may be more common under climate change conditions, to see how their plan manages stormwater.

Feedback from property developers has been positive, as the tool enables them to understand the benefits and efficiencies LID can bring to traditional stormwater management design. The tool has cleared away what had been a frustrating part of the planning experience. Regulators, for their part, are glad to have developers using a common tool, so they can make more informed judgements about the efficacy of the developer’s proposal.

The result will be property development that minimizes impacts on water resources and mimics the natural systems in place prior to development, thereby minimizing flooding, allowing groundwater recharge, and treating surface water prior to entering our streams and rivers.

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About the Author

Chris Davidson

Christopher Davidson Member Name

P.Eng., Surface Water Engineer

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