A further challenge was to use modern LID techniques, yet still achieve traditional SWM objectives. These include erosion control, pre- to post-water quantity control for many design storms, 80% removal of suspended solids, and water balance. Also, maintenance staff and the Town’s peer review consultants had to be confident that no undue maintenance burden or liability exposure was being incurred as a result of the proposed works.
It should be noted that this unconventional solution was given a design objective of 25 mm of rainfall for site retention, five times the conventional standard.
Biofiltration swales contributed a lot to water quality, but in different ways. In some cases, topography and land use allowed small areas to have direct stormwater flow into biofiltration swales. Also, roads with continuous cross-fall were utilized to convey stormwater to these types of biofiltration facilities adjacent to perimeter roads. In another case, a much larger area utilized a treatment train approach. This resulted in water being treated first by oil/grit separators to remove heavier suspended solids, then polished by a downstream biofiltration facility and finally released to a watercourse that traverses the site.
Rain gardens, a variation of biofiltration swales, were also situated throughout the site at many of the intersections to promote unconventional SWM systems. Lots adjacent to the rain gardens were found to be very desirable and were among the first to be sold.
Subscribe to our Newsletter!
The latest environmental engineering news direct to your inbox. You can unsubscribe at any time.
In addition to the biofiltration swales, the LID design also featured a stormwater exfiltration system, or a groundwater infiltration system, under roughly half of the roads throughout the development. The exfiltration trench is fed road runoff (prefiltered by a goss trap) in order to retain the most frequent storm events. Exfiltration provides a major contribution towards the 25 mm retention objective, especially in the sandier soil areas. Planned future monitoring of this system will eventually measure the true amount of exfiltration or groundwater infiltration.
Given the unconventional nature of the proposed LIDs, the design engineer was present at bi-weekly construction meetings to ensure contractors understood the drawings, the objectives and limitations of the design. This is important because some LID techniques, such as biofiltration swales, can be very sensitive to construction activity. For example, heavy construction equipment can easily crush a biofiltration swale and render it useless. Therefore, methodology, control of materials and timing of installation can be crucial to successful implementation of LID facilities.
An important aspect to the evolution and outcome of LID in this project was the cooperative involvement of Bazil Developments Inc. and Mosaik Homes, the General Manager of the Lake Simcoe Region Conservation Authority, and the Chief Administrative Officer of the Town of Newmarket.
The Vales of Glenway residential subdivision is a pioneer in the application of low impact development stormwater management techniques. By monitoring these techniques, it is hoped they will evolve for future application in the design of more hydrologically sustainable developments.
Harold Reinthaler, P.Eng., is with Schaeffers Consulting Engineers. This article appears in ES&E’s November/December 2015 issue.
It’s interesting how you said that stormwater drainage in some areas is designed to mimic the hydraulic function of a specific site. This would be really great in our yard because it used to be part of a farm before it was ruined because of lack of nutrients. There are some excellent grooves and things like that, so we’ll have to look into this kind of thing to see if it would help to keep our house from flooding.
It sure was nice to know the LID works with other natural processes in order to reduce surface water runoff and help stabilize the flow rate of nearby streams at the same time. That sounds environmentally friendly, and I think my boss will prefer this option for the construction. After all, he is concerned with the success of the structure he wants to be made, but he is also concerned for the surrounding which the building will be erected on.
This looks like a very good project!