Effect of Urbanization on Base Flow Hydrology Among Ecoregion II Catchments in Eastern United States

Urbanization is a common parameter discussed among hydrologists and its effect on base flow hydrology and the 7Q10 [seven Q ten] statistic varies wildly. Population growth and urban development has grown at an alarming rate in recent years; especially in the Southern and Mid-Atlantic United States. This is due to the fact that 50% of the world’s inhabitants live in cities and over 500 cities house more than 1 million people. Development as it sprawls from urban centers is thought to have negative effects on groundwater recharge and the 7Q10. There are still questions as to how urbanization effects stream base flow. Much focus has been made regarding the use storm water control measures to control peak flows, but literature lacks analysis on the effect of urbanization on stream base flow. This study seeks an understanding of the combined effect or increased urbanization and drainage area size on the 7Q10. This study also examines the effect of reduced forest volumes on watershed hydrology. The aforementioned parameters will be the focus of more in-depth research surrounding the hydrologic responses of 95 catchments in US EPA Eco-Region II. The 95 catchments are a mixture of urban and rural and vary size from 8,815 mi2 [miles squared] to 4 mi2. These catchments are randomly selected inside the relatively large scale homogenous ER2 [eco region two] in an effort to detect trend that may not be visible via small more geographically concentrated studies. The 7Q10 was calculated for each gaging station and related to land cover attribute from the 1992 and 2006 NLCD. Strong correlation was found when relating the 7Q10 to drainage area. Thus, signifying a need to normalize the 7Q10 to drainage area and use this parameter as the response variable for regression. Regression shows a distinct lowering in 7Q10 at the 15-20 % [percent] urbanized situation. This result signifies that an increase in urbanization ultimately reduces the capacity of a watershed to process precipitation and recharge aquifers. The fact that 50-90 % of the true base-flow is from groundwater flow to streams only further proves this hypothesis