Managing Urban Wet-Weather Flows: On the Road to Sustainability

The management of urban wet-weather flows, and particularly of combined sewer overflows (CSOs) and stormwater discharges, continues to attract attention worldwide. Obvious examples of this interest include the recent U.S. EPA report to Congress on the impact and control of CSOs and sanitary sewer overflows (SSOs) (U.S. EPA 2004) and the European Union Water Framework Directive emphasizing the need to attain the “good” status for surface waters in terms of chemistry and ecology (Mohaupt 2004). The situation in Canada is no different, with many ongoing or recently completed projects on sustainable infrastructure for stormwater management (National Guide to Sustainable Municipal Infrastructure 2003), guidance documents for stormwater management planning (British Columbia Ministry of Water, Land and Air Protection 2002; Ministry of the Environment 2003), CSO treatment (XCG Consultants Ltd. 2004), and many other reports on planning and engineering studies. In response to this Canada-wide interest, the Guest Editors enthusiastically accepted the invitation from Dr. R. Gehr, Editor of the Water Quality Research Journal of Canada, to prepare a theme issue on urban wetweather flows, and secured funding from the Government of Canada’s Great Lakes Sustainability Fund. This issue builds on the success of the two earlier ones on similar topics, which were published in 1997 and 2000, under the titles “Great Lakes 2000 Cleanup Fund Program: Stormwater Management and Control of Combined Sewer Overflows” (Water Qual. Res. J. Canada, Vol. 32, No. 1, 1997) and “Urban Stormwater Management for Ecosystem Protection” (Water Qual. Res. J. Canada, Vol. 35, No. 3, 2000), respectively. While the earlier issues focused only on studies in the Great Lakes basin conducted with co-sponsorship of the Great Lakes Sustainability Fund (GLSF), no such restrictions apply to the current issue. The Guest Editors approached potential contributors in all regions of Canada, and finally, the only limiting factor was a demanding time schedule, as the entire project had to be accomplished in about nine months. Many authors accepted this constraint and the result is the following collection of 14 papers. These papers provide a good balance between the two major topics, with about a half of the papers dealing with stormwater and the other half with CSOs. The management of urban stormwater is of concern in many Canadian jurisdictions, particularly in connection with the principles of sustainable development. There have already been many success stories on the road to sustainability. Such a goal is, however, difficult to achieve without addressing the issue of sustainable communities, or the sustainability of the entire watershed, because some of the required management measures extend beyond the municipal authority and require a concerted action of all stakeholders. One example of such an over-arching action is building product (material) substitution, which may prevent the use and release of chemicals of potential concern into stormwater (Clark et al. 2002). Increased interest in source controls (as a form of prevention) has been noted in the literature and has led to a new term “rainwater management.” This approach emphasizes maintaining a pre-development water balance on site (e.g., by infiltration and reduced catchment imperviousness), control measures targeting smaller rain events conveying a large proportion of the annual rainfall, etc. This new expression confirms a continuing search for the “best fitting” terminology in this field, which often reflects a particular practice, or contemporary terminology in other fields related to stormwater management. Historically, various aspects of stormwater management have been called urban runoff controls, alternative techniques, best management practices (BMPs), sustainable urban drainage systems (SUDS), low impact development (LID), and water sensitive urban design (an Australian expression). One can argue that rainwater management represents a type of source control applied in stormwater management, which was defined by Marsalek (2001), as “the measure designed to control the generation of, and entry of pollutants into, stormwater runoff, with emphasis on non-structural and semi-structural measures applied at or near source.” It is the Editors’ opinion that the rainwater management term describes the concepts included in advanced stormwater management. To illustrate this point, one can cite from older (seminal) literature; e.g., the ASCE