Porous Bituminous Pavement: A Stormwater Best Management Practice

As development occurs and impervious surfaces increase, we are faced with not just an increase in stormwater peak rates, but a tremendous increase in the amount of stormwater volume generated. Traditional methods of stormwater management, such as detention, often fail to address stormwater volumes. At the same time, infiltration to groundwater and recharge to the aquifers is decreased by the impervious surfaces and our practice of collecting and conveying water downstream. The impacts on streams are dramatic. During non-storm periods, baseflow is reduced and streamflow diminishes, but during even moderate rainfall events, streams in developing watersheds can quickly overtop their banks, causing localized flooding. The physical changes in the stream channel can cause loss of habitat and loss of biological diversity. Stormwater runoff is the primary cause of impairment in many urban streams. Sustainable stormwater management requires that we address not just peak rates but the increased volume of runoff, and that we attempt to mimic the natural hydrologic balance that existed before development. Design approaches and infiltration methods are the most effective means to do this, but require a change in approach to site development. In this paper, we will present a number of stormwater infiltration methods, and discuss their design and application on specific projects, including a number of installations of porous bituminous pavement that have been performing effectively for almost twenty years. We will also present applications of infiltration meadows, trenches, swales, porous concrete sidewalks, bioretention gardens, and other approaches. The design, installation, and performance of these methods at actual sites will be discussed, as well as "lessons learned" and the effectiveness of infiltration methods in reducing non-point source pollution.