Observation of urban karst flows inform planning, design and construction of green stormwater infrastructure

This is the authors' abstract. We don't add key points for this paper.

Rapid increases in population worldwide have led to an expansion of areas characterized by highly connected impervious surfaces. Located beneath these surfaces are intertwined layers of infrastructure, such as pipes, gravel-filled trenches, and wires, transporting utilities and water. Engineers have increasingly adopted infiltrating stormwater control measures (SCMs) to more closely mimic pre-development hydrology and mitigate the detrimental effects of impervious cover on receiving waters. When constructing SCMs, there is the potential for stormwater to unintentionally discharge via alternate pathways along subsurface infrastructure, particularly when retrofitting into existing urban developments which requires disturbing the subgrade and potentially relocating utilities. Interactions between infiltrated stormwater and this complex system of subsurface infrastructure, or the ‘urban karst’ phenomena, are an anthropogenic corollary to the natural tunnels and underground channels that can be found in geologies with highly soluble rock such as limestone. Relatively few studies have explored the impacts of urban karst pathways on the performance of infiltrating SCMs. This study explored three SCMs with known urban karst interactions in Ohio and North Carolina (USA) to better understand the potential impacts of urban karst SCMs. Alternate drainage pathways were confirmed using methods such as long-term monitoring, sewer inspection cameras, and dye tracer studies. Recommendations for design techniques, such as impenetrable liners in SCM installations, that could be implemented to minimize the urban karst effect are also explored. Given potential unintended consequences of urban karst and the prevalence of underground infrastructure worldwide, engineers are encouraged to consider these techniques in all SCM designs.