Sustainable Construction of Existing Wetlands for Urban Stormwater Management

Implementing an existing natural wetland into a new urban stormwater management facility can improve the sustainable aspects of the new development by providing increased social and environmental benefits and decreasing costs. Retaining an existing wetland has challenges due to the characteristics of its ability to handle the new hydrology and lower water quality from the urban stormwater runoff. There is limited literature available on implementing existing wetlands for stormwater control; however, constructed wetlands are an accepted and proven practice. Attempts to use natural wetlands require them to be modified to replicate constructed wetlands to facilitate regulatory approval. This is due to the lack of understanding of how natural wetlands will behave under a new stormwater flow regime. Low impact design (LID) measures are gaining wider acceptance, and there is promise in combining these measures with a natural wetland to provide stormwater management for both hydrology control and water quality improvement. Potential success of wetland retention requires a comprehensive understanding of the existing physical, chemical, and ecological parameters of the wetland, as well as modelling of the urban stormwater runoff to predict compatibility and inform possible upstream LID requirements. Using the case study of the Michael Rawson Clark Natural Area currently being implemented in Edmonton, Alberta, the physical, chemical, and ecological parameters of the existing wetland are established, and modelling using the rational method and PCSWMM for future stormwater flows with LID measures are considered to determine the potential sustainability of retaining this wetland to handle and treat new, urban stormwater flows. The methodology developed is applicable for future wetlands in considering retention in lieu of removing and replacing with a man-made structure.