A HISTORICAL, EMPIRICAL ANALYSIS OF THE RELATIONSHIP BETWEEN URBANIZATION AND STREAM BASEFLOW IN THE EASTERN UNITED STATES

Over the last century, the population density has more than tripled which has placed greater anthropogenic influence and increased urbanization in historically rural watersheds. A major result of urbanization is increased impervious surfaces due to the construction of roads and homes as well as the compaction of soils. In permeable soils, precipitation infiltrates and recharges the groundwater, which is the source of stream discharges, or baseflow. With an increase in urbanization in a watershed one would theoretically expect a decrease in infiltration and therefore a decrease in ground water recharge and baseflow. Reduced baseflow can directly limit water availability for approximately half the U.S. population that depends on surficial waters for their drinking water. While in theory the relationship is sound, additional processes associated with urbanization such as irrigation and leaking water pipes and storm /sanitary sewers confound the connection between urbanization and baseflow. The goal of this project is to empirically investigate how urbanization has impacted stream baseflow on a geographic and temporal scale that has not been previously investigated. The project uses USGS gage data from streams in 10 East Coast states, which share similar physiographic provinces (NY below the Adirondacks, CT, NJ, PA, DE, MD, VA, NC, SC and GA). Stream gage data were gathered under the criteria that the data was continuous (≥25 years), unregulated, and of a drainage area ≤400mi². Three metrics of annual baseflow used are 1) baseflow per unit drainage area (BF); 2) ratio of BF to precipitation (BF/P) 3); and BF as a fraction of total flow (BF/TF). Using population density as a proxy for urbanization, IBM SPSS Statistics software was used to run panel data fixed effect models to detect trends. Results from 50 unregulated streams with significant trends show that for every 1% increase in population density there is a corresponding decrease in BF of 6.1%.The next step is to expand on the current dataset by running statistical analysis on additional gages and time series as well as incorporating the BF/P and BF/TF metrics. The results will determine if there is a relationship between urbanization and baseflow as well as provide water managers with a way to assess the threat that urbanization poses to dry-weather water availability.