Low Impact Development (LID), a stormwater management approach that uses natural elements, has gained popularity across Canada and the United States over the past decade. Here, Ian Smith of Urban and Environmental Management explains the strategy and how it embraces water as a valuable resource.

How would you describe Low Impact Development (LID)?

In the context of water resources and specifically stormwater management (SWM), Low Impact Development (LID) is an attempt to develop lands within the framework of a natural or undisturbed water balance. This means that the precipitation falling on a parcel of land will experience the same infiltration, evapotranspiration, storage (in ponds, lakes, wetlands and aquifers) and ultimately runoff as it did previous to its development. Furthermore, the means to achieve this preservation of the parcel’s water balance should mimic the natural hydrologic cycle in every way possible. LID techniques represent a wholesale change in our approach to water management; water is seen as a valuable resource as opposed to a waste product.

What advantages does LID hold over other stormwater management strategies?

Traditional SWM practice has focused on detaining or delaying increased surface runoff (due to paving and grading) using storage facilities (wet and dry ponds). The discharge of water away from the property as quickly as possible was still promoted, though. While this very often successfully reduced flood and erosion risks on the property itself, it did little to protect receiving waters that the storm flows were directed to. This approach also did nothing to enhance the local ecology with high quality habitat.

Since the natural water balance for a given property has evolved over many years (approximately 13,000 years in the context of southern Ontario; post glaciation), the channels that drain runoff for that property are typically robust enough to protect the land from significant damage due to flooding and erosion. The maintenance of historic infiltration of water into soils (and thus the groundwater table) serves to sustain nearby streams, wetlands and lakes as well.  Preservation of pre-development evapotranspiration necessitates the preservation of some significant amount of vegetation and tree canopy.

This not only benefits the local ecology, but typically improves nearby property values. Essentially, nature is showing the designer what strategies are optimal for stormwater management. A wise stormwater system designer will mimic the natural hydrologic processes as closely as possible. The U.S. Environmental Protection Agency (EPA) has even gone so far as to coin the term ‘Green Infrastructure’ to promote the use of this mimicry of natural processes in stormwater management.

What kinds of properties and areas are best suited for LID?

Our firm has successfully undertaken the use of LID components in numerous, diverse settings. These range from small residential developments through larger community master plans and commercial developments, to industrial applications and municipal or industrial landfills. It is noteworthy that LID techniques can – and should – be utilized in property redevelopments and retrofits as well as in new developments. This is often a challenging, yet very rewarding aspect of our firm’s work. Techniques have ranged from very simple and small areas of pervious pavement to the creation of full-scale stormwater treatment wetlands.

Are there any other alternatives to LID that you would recommend?

We recommend the use of LID components in SWM to all of our clients; thus, in our minds, there is not really an alternative. Some clients are reluctant to work towards LID due to a perception of increased capital costs (when compared to traditional methods discussed above). However, it is important to note that the higher capital costs, or up-front costs, are often easily and quickly offset by reduced life-cycle costs, liability and risks related to downstream flooding and erosion.

There are also huge benefits to be realized via the marketing of a property development as having a positive net benefit for the provision of wildlife habitat and the associated ‘human ecology’ in general.  Local governments and environmental agencies, including conservation authorities, are increasingly demanding the use of LID techniques to protect various fish and wildlife species.

Ian Smith is a fluvial geomorphologist for Urban and Environmental Management, a consulting firm with offices throughout Ontario.