EVALUATING GREEN INFRASTRUCTURE DESIGN TO MITIGATE URBAN RUNOFF IN BUFFALO, NY

The city of Buffalo, NY, has been investing in Green Infrastructure in the form of bioretention cells to reduce the volume of stormwater runoff entering the combined sewer system (CSS). By capturing runoff before it enters the CSS, bioretention cells can reduce the impacts of combined sewer overflows (CSO) which discharge pollutants into local water bodies, including Lake Erie and the Niagara River.

The objective of this research is to investigate the performance of various bioretention designs through a combination of field experiments and variably saturated flow modeling in HYDRUS 2D. The models incorporate the unique design configurations of bioretention on Niagara Street, and evaluate how changes in parameters such as length, depth, soil type, inlet location, root water uptake, and the presence of a geomembrane could impact performance targets such as storage and peak flow reduction. Our goal is to identify an optimal bioretention cell design for a given set of climatic conditions that maximizes water storage capacity, reduces peak outflow, and increases the lag time between precipitation and outflow. The findings of this research have implications for optimizing bioretention cell design to account for differences in water storage and peak flow reduction capacity, which directly impact the ability of these structures to attenuate runoff before entering the CSS.

Field and model results indicate that antecedent soil moisture conditions play a significant role in the hydrologic performance of bioretention cells. Model results indicate that an increase in soil depth by 50% could reduce peak flows from bioretention cells by as much as 90%, and that an additional inlet could reduce peak flows by as much as 52%. Model results also reveal that the current bioretention cell design, which focuses infiltration in small areas, bypasses the opportunity for storage in adjacent unsaturated soils. Potential storage capacity is also lost in structures that include a geomembrane.