The location choice of green infrastructures and their hydrologic effects in shallow groundwater environments

Abstract

Green infrastructures (GI) are effective in controlling surface runoff, reducing non-point source pollution, and restoring pre-development hydrologic cycle. Studies have been performed to evaluate the appropriate designs and planning strategies of GI to maximize their benefits in water quantity and quality management. However, very few studies considered their influence on groundwater and the influence of groundwater on their performance, which are beneficial to GI planning particularly in shallow groundwater areas. In this study, a surface-subsurface coupled hydrological model, SWMM-MODFLOW, was utilized, which was calibrated and validated based on the monitoring data in one urban catchment in Silverdale, Washington, U.S. Based on the calibrated model, the influence of GI spatial allocation on surface runoff and groundwater table dynamics was evaluated. The implementation ratio, aggregation level and location of GI all influenced the surface runoff and groundwater table dynamics. With more GI practices implemented, more runoff can be controlled and the groundwater table would rise more, but the uniformity of regional groundwater condition was not significantly affected. Besides, targeting at high runoff control efficiency and uniform groundwater condition, the near-optimal spatial allocation of GI for different planning objectives and environmental conditions (i.e., rainfall characteristics, groundwater conditions, and soil properties) was determined. More GI practices tended to be implemented in areas of wetter climates and gentler regional groundwater hydraulic gradients. GI practices tended to be allocated spatially distributedly for all different conditions, but more upstream (downstream) areas would be preferable for areas of steeper (gentler) groundwater hydraulic gradients and when groundwater management (surface runoff control) was more focused on.