Urbanization threatens headwater stream ecosystems globally. Watershed restoration practices, such as infiltration-based stormwater management, are implemented to mitigate the detrimental effects of urbanization on aquatic ecosystems. However, their effectiveness for restoring hydrologic processes and watershed storage remains poorly understood. Our study used a comparative hydrology approach to quantify the effects of urban watershed restoration on watershed hydrologic function in headwater streams, located within the Coastal Plain of Maryland, USA. We selected 11 headwater streams that spanned an urbanization–restoration gradient (4 forested; 4 urban-degraded, 3 urban-restored) to evaluate changes in watershed hydrologic function from both urbanization and watershed restoration. Discrete discharge and continuous, high-frequency rainfall-stage monitoring were conducted in each watershed. These datasets were used to develop six hydrologic metrics describing changes in watershed storage, flowpath connectivity, or the resultant stream flow regime. The hydrological effects of urbanization were clearly observed in all hydrologic metrics, but only one of the three restored watersheds exhibited partially restored hydrologic function. At this site, a larger minimum runoff threshold was observed relative to urban-degraded watersheds, suggesting enhanced infiltration of stormwater runoff within the restoration structure. However, baseflow in the stream draining this watershed remained low compared to the forested reference streams, suggesting that enhanced infiltration of stormwater runoff did not recharge subsurface storage zones contributing to stream baseflow. The highly variable responses among the three restored watersheds were likely due to the spatial heterogeneity of urban development, including the level of impervious cover and extent of the storm sewer network. This study yielded important knowledge on how restoration strategies, such as infiltration-based stormwater management, modulated – or failed to modulate – hydrological processes affected by urbanization, which will help improve the design of future urban watershed management strategies. More broadly, we highlighted a multi-metric approach that can be used to monitor restoration of headwater stream ecosystems in disturbed landscapes.
Read the full article in Hydrological Processes.