Since moving to the interior of British Columbia back in 2007, I have had many discussions with engineering types about the benefits of the alternatives to the curb and gutter / catchbasin paradigm. Interestingly, even six years later there really isn’t that much good knowledge out there on the cost of installation and maintenance of these systems, particularly in areas where heavy snowfalls or road sanding requirements might change the maintenance and operation requirements.
I’m convinced that in lower density residential areas, swales can be an appropriate design, and in the right conditions, may be supplimented with intentional infiltration devices. But the concerns that keep coming up from operations staff have not changed over the years:
- ditches/swales get infilled by homeowners
- driveway culvert inlets and outlets are not maintained by homeowners
- road sand clogs the infiltration capacity of the swales
- road sand will build up, requiring heavy equipment to remove
- road edges are more difficult to preserve and maintain without curb and gutter
- ponding can promote mosquito breeding
- most studies estimate that the installation cost of swales is less than half of conventional curb and gutter costs.
- swales reduce storm peaking, reducing downstream erosion
- swales reduce pollutant loading
- swales allow water to get off the road, whereas curb and gutter concentrates flow to a catchbasin, usually causing water to spread across the road in larger storms
- swales provide a more natural road edge
- swales are both the collection and conveyance, rather than curb and gutter, catchbasins and stormwater pipes / manholes