Streamflow Dynamics Across an Urbanizing Karst Watershed in the Ridge and Valley Province

Effective freshwater management depends on understanding how human activities and geological processes influence streamflow dynamics. Urbanization disrupts natural hydrological processes, altering both stormflow and baseflow. Karst watersheds, characterized by complex and heterogeneous surface-groundwater interactions, pose unique challenges for predicting the impacts of urban development on streamflow. This study investigates how urbanization and karst groundwater interactions influence streamflow variability in a mixed land-use watershed within the Ridge and Valley Province of central Pennsylvania. We analyzed 24 years (2000–2024) of streamflow data from 14 monitoring stations spanning gradients in urbanization (10%–90% developed land) and karst geology. Streamflow metrics including flow duration curves, baseflow index, Richards-Baker flashiness index, master recession curve slopes, and low-flow trends, were used to assess land use and groundwater controls. Urbanization increased stream flashiness, steepened recession rates, and decreased the proportion of base flow. Streams with the highest levels of development exhibited most sensitivity to further increases in urban land cover. In contrast, streams with substantial groundwater inputs exhibited more stable baseflows and were less sensitive to drought conditions. Stormwater infiltration and wastewater recycling supported low-flow regimes, partially offsetting development effects, whereas recent growth combined with groundwater withdrawals led to reduced low flows in some areas. These findings highlight the need to account for hydrological complexity and groundwater recharge when managing water resources in increasingly urbanized karst watersheds.