Connecting the Regional Blue with the Local Gray and Green: Field Assessment of Hydrologic Capacities in Post-Urbanized Landscapes and Signaling Their Status (Detroit MI)

Sustainable and resilient hydrologic urban ecosystem services rely on connectivity among gray, green, and blue infrastructures. Yet, few of these services are quantified nor readily translated to inform management and policy regarding hydrologic connectivity. We eval-uated typically extensive and contiguous vacant parcels in the River Rouge, and Detroit River watersheds, which nominally drain the west, east sides of Detroit MI (USA), respec-tively. To gauge gray, green, blue connectivity, we measured parcel soil hydraulics as in-filtration and drainage rates, collected soil taxonomic data, and identified the depth of the groundwater table. Hydraulic data was sorted by an intuitive “stoplight” approach, with green, yellow, orange, red categories signaling hydrologic prospects, limitations, and gen-eralized management. With notable exceptions as green or yellow summary ratings, gray-green connectivity was limited due to variability in fill soil source, type, and layering. Blue assets as groundwater and river courses are largely decoupled from green due to perched water tables, and gradients altered by adjacent freeway dewatering. This assessment process can serve to optimally allocate city resources under what are highly variable hydrologic conditions, and toward effectively and efficiently sustaining ecosystem services where they are most strongly rendered among gray, green, and blue water regimes.