More than 100 case studies from the published literature were reviewed to compile simplified, representative water budgets for green and gray stormwater infrastructure systems, including retention and detention ponds, green roofs, bioretention cells, porous pavement, natural and constructed wetlands, and other stormwater control measures. Then, the long-term cumulative water budgets for these systems were compared using a ternary plot tool called the Water Budget Triangle, which quantifies hydrologic performance to address the fundamental question: “How does water leave a closed system?” Understanding the underlying physical, ecological and hydrologic controls on individual stormwater strategies helps to identify appropriate management alternatives for specific sites. This information has utility for planners, engineers and decision-makers who must consider small, catchment-scale ecohydrology to effect change at the watershed scale. The results of this study help consolidate diverse stormwater management strategies into a unified set of green and gray stormwater tools, which are based on real-world data.
This study aims to overcome communication barriers currently limiting green infrastructure implementation, and facilitate the following: 1) conveying technical information about green and conventional stormwater devices to both technical and lay stakeholders and decision makers; 2) providing a unifying visual aid to compare performance of dissimilar systems; 3) eliminate non-technical uncertainty in language representing stormwater best management practices; and 4) develop an understanding of ecological factors affecting stormwater systems that are often excluded from urban ecology. To do this, physical and ecological co-variables were examined alongside water budgets to understand site-specific controls on hydrologic performance. Understanding the underlying ecohydrology of each type of structure allows pertinent design, maintenance and retro-fitting changes to become obvious and implementable ways of improving long-term hydrologic retention and realizing water quality benefits. For example, evaporation is a significant loss pathway for many stormwater management structures, including detention ponds and porous pavement systems, but this variable is frequently ignored during modelling and design stages. Design modifications that augment stormwater capture by increasing evaporation or transpiration from detention ponds and porous pavement would improve overall volumetric reduction on site, thus reducing stormwater runoff. This talk describes the representative hydrology of each structure type, discusses physical and ecological controls at the site level, and makes suggestions for management or design changes that may beneficially influence hydrologic performance.