Investigating the Performance of Simple Rain Gardens in Guelph
Increasing amounts of impermeable surfaces within urban centers lead to increased runoff during storm events, causing detrimental effects to our infrastructure and environment. New stormwater management technologies have been developed to counter these effects. They attempt to slow the flow of stormwater and prevent movement of pollutants by keeping water on-site and facilitating its infiltration into the ground. These technologies are commonly known as low impact development (LID) or sustainable stormwater management (SSM). Rain gardens – also known as bioinfiltration facilities - are a form of LID. Many studies on rain garden optimization have led to guidelines being widely available on LID construction. However, these requirements are often unrealistic for small-scale projects and present implementation barriers. An alternative to bioinfiltration facilities are simple rain gardens (SRGs) that have no underdrain and are often created in existing soils. This investigation measures infiltration rates, soil composition, and sizing of five case study SRGs in Guelph, and assesses their performance via percentages of influent stormwater detained, and total volumes detained annually. Analysis reveals three of the five case studies to be performing at full capacity, even though their soil compositions do not reflect what is commonly considered optimal for infiltration performance. The remaining two case studies were found to perform a value function by infiltrating between 36 and 45% of the stormwater directed into them, but adjustments to their size would need to be made in order to reach 100% infiltration. All together these SRGs would detain around 300,000L of stormwater annually.