Connecting Local Gray and Green Infrastructure with the Regional Blue: Field Assessment of Hydrologic Capacities in Detroit MI USA

Sustainable and resilient hydrologic urban ecosystem services rely on connectivity among gray, green, and blue infrastructures. We conducted a field study of post-urban landscape hydrology in inland (River Rouge) and coastal (Detroit River) catchments on the West and East sides, respectively, of Detroit, MI. Measurements of parcel (n = 36) soil hydraulics as infiltration and drainage rates, soil taxonomic data, and depth of the groundwater table were used to determine connectivity. Hydrologic data was parsed into “stoplight” categories (green, yellow, orange, red) that at once communicate connectivity and best uses for sustained rendering of ecosystem services from vacant parcels. Parcels with yellow, orange, and red infiltration rates would respond to tillage and cover cropping with an increase in gray-green connectivity, whereas drainage rates in the orange and red categories suggest redevelopment. Blue-green connectivity was constrained by high variation in drainage rate, perched versus deeper saturated zones, urban drainage affecting local groundwater gradients, and relatively little groundwater data to compare against. This assessment process can serve to optimally allocate city resources to effectively and efficiently identify best management practices (including redevelopment) for vacant sites and to sustain ecosystem services, where they are most strongly rendered as connectivity amongst gray, green, and blue water regimes.