Stormwater Storage and Retention Within an Urban Prairie Wetland Complex

Abstract

Climate change is expected to increase the frequency and severity of flooding in the Great Lakes region. In many cities, flood‐control infrastructure is insufficient to protect against future climate conditions. Consequently, there is increasing focus on stormwater storage provided by urban greenspace, such as wetlands and prairies, but the ecohydrological behavior of these ecosystems is not well understood when they are embedded within cities. To improve understanding of hydrological connectivity between urban areas and natural greenspaces, we deployed a sensor network in Gensburg Markham Prairie (GMP), a large intact prairie‐wetland complex in south suburban Chicago. We used the resulting high‐frequency time‐series data to assess surface‐subsurface hydrologic dynamics between upland and low‐lying wetland areas, interactions between the prairie and surrounding environment, and stormwater storage provided by the prairie. Rapid infiltration within the prairie during and after storm events provides subsurface flow that stores considerable water, flattens storm hydrographs, and increases the wetland hydroperiod. Much of the stormwater input to GMP derives from the surrounding cityscape. Consequently, storage within the prairie‐wetland system reduces and slows stormwater discharge to downstream urban communities. For a typical 5‐year 24‐hr storm with 10.9 cm of rain, GMP stores 77,100 m³, 64% greater than the estimated direct rainfall volume onto the prairie, yielding 30,000 m³ of offsite stormwater storage. This improved understanding of ecohydrological dynamics in urban prairies and wetlands informs the design and implementation of green infrastructure to meet growing needs for stormwater management.