HR: 1330h
AN: NB33O-03    [Abstracts]
TI: Quantifying Baseflow Declines due to Increased Imperviousness in Urbanizing Watersheds
AU: * Brandes, D
EM: brandesd@lafayette.edu
AF: Lafayette College, Dept of Civil & Env Eng, Easton, PA 18042
AU: Brandes, C A
EM: kbrandes@wildlandspa.org
AF: Wildlands Conservancy, 3701 Orchid Place, Emmaus, PA 18049
AB: Land development and the associated increase in imperviousness are generally expected to cause the following two effects on streamflow: 1) increasing storm runoff volumes and peak flows; and 2) decreasing baseflow volumes and low flows. It has been suggested that the second effect is a necessary result of the first. This paper describes several case studies of baseflow trends in urbanizing watersheds based on long-term streamgage data from the northeast U.S. Hydrograph separation is used to determine annual baseflow volumes and trends are analyzed using nonparametric methods. Results show that urbanization has a variety of possible effects on baseflow. Instances of rapid declines in baseflow are due to anthropogenic water-balance alterations, such as groundwater use coupled with wastewater export from the watershed, not simply a result of increasing imperviousness. Such cases show a characteristic decline in annual total water yield (Q/P) and should not be used to infer the effect of imperviousness. The results also show that in the absence of significant interbasin transfers, decreases in baseflow are generally lower in magnitude than increases in storm runoff caused by increased imperviousness. It is suggested that this is due to: 1) reduced evapotranspiration losses; 2) leakage from water and sewer infrastructure; 3) reinfiltration of runoff from upland areas of the watershed; and 4) land development in groundwater discharge zones where there is little effect on watershed recharge.
DE: 1803 Anthropogenic effects
DE: 1829 Groundwater hydrology
DE: 1836 Hydrologic budget (1655)
DE: 1860 Runoff and streamflow
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly