Evaluation of the hydrologic benefits of infiltration-based stormwater management

As watersheds are urbanized, their surfaces are made less pervious and more channelized, which reduces infiltration and speeds up the removal of excess runoff. Traditional stormwater management seeks to remove runoff as quickly as possible, gathering excess runoff in detention basins for peak reduction where necessary. In contrast, more recently developed "low impact" alternatives manage rainfall where it falls, through a combination of enhancing infiltration properties of pervious areas and rerouting impervious runoff across pervious areas to allow an opportunity for infiltration. Using small-scale infiltration practices distributed throughout a watershed seems to offer a promising solution to managing stormwater quantity and quality, while still maintaining aesthetics and ecological integrity.; An in-depth review is made of existing programs and practices seeking to implement more integrated stormwater management as priorities move beyond simply managing stormwater quantity and quality into more ecosystem-based, environ mentally friendly strategies. In addition, a review of the factors and processes that influence infiltration rate aid in formulating specific research goals. Through infiltration measurements made in the field, it was possible to address the question of how vegetation affects infiltration rate. Although the original research questions remain unanswered, the experience aided in the development of an automated infiltrometer design. Finally, hydrologic modeling was used to evaluate infiltration-based stormwater management. A group of preliminary experiments using simple engineering tools evaluate conceptual scenarios, comparing undeveloped, low impact development, and traditional development. These experiments demonstrated that low impact development is most effective at mitigating urbanization effects for the small, frequent rainfall events. Furthermore, these techniques were found to be most effective for more pervious soils, as adding impervious surfaces over soils with low infiltration capacity created relatively smaller impacts. In addition, one-dimensional continuous simulation was used to study one low impact practice in detail. This demonstrated the feasibility of using compost-amended soils to enhance infiltration to absorb runoff from nearby impervious surfaces. From these experiments, preliminary design guidance for selection of amended depth and area was developed.