THE EFFECTS OF CHANGES IN POPULATION DENSITY ON RIVER BASEFLOW FOR THE MIDWESTERN UNITED STATES

River baseflow is the discharge supported predominantly by groundwater, and can be greatly impacted by changes in land use. Intuitively, river baseflow might decrease with increased urbanization, as the increased impervious surfaces limit the infiltration and subsequently limit the recharge of the local groundwater. However, evidence suggests that the river baseflow in urbanizing areas can also increase as a result of leaky subsurface water infrastructures that add water to groundwater and replenish baseflow. Another reason for the baseflow increase in urbanized watersheds is that water supply systems are over-pressurized by design to reduce the chances of contamination, contributing extra water to the local system. Cities that have decreased in population over the last several decades may experience an even greater addition to baseflow as aging, leaky water infrastructures may not be attentively maintained due to the fact that there are less people in the area to supply water to. Given these conflicting urban influences on baseflow, it is important to investigate this relationship further. The goal of this project is to empirically investigate how decreased population in urban areas has impacted baseflow in the Midwestern region of the U.S. The project uses USGS gage data from streams within the Rust Belt, specifically from the states of MI, NY, PA, and OH. Stream gages were selected that were continuous (≥40 years), unregulated, and a drainage basin of ≤400 square miles. Six metrics of annual discharge used are 1) baseflow per unit drainage area (BF, m3/yr); 2) runoff (RO, m3/yr); 3) total flow (TF, m3/yr); 4, 5, & 6) and a ratio of these flows to precipitation over area (BF/P/A; RO/P/A; TF/P/A, unitless). The results determined that there is mainly a positive relationship between depopulation and baseflow in cities that lie within the geophysical province of the Central Lowlands (8 out of 12), possibly due to higher permeability of the regional lithology.