TRANSVERSE DRAINAGES, DIVIDES AND LANDSCAPE EVOLUTION IN THE GREAT VALLEY, EASTERN UNITED STATES

The processes controlling landscape evolution in the Great Valley, eastern United States is a controversial topic. The Great Valley was used to test two paradigms of landscape evolution; dynamic equilibrium (Hack, 1960) where the relief of the landscape remains constant even if there are changes in total elevation or position and that of W.M. Davis (Davis, 1889, 1899), which explained a landscape in slow decay from high relief to a peneplain that grades gently to base level. This study proposes to rectify these two apparently opposing paradigms using the landscape of the Great Valley. Consistent lithologic patterns for the Great Valley lead to consistent drainage patterns for each basin in the Great Valley. Generally, each basin has two major drainages that trend parallel to the strike of the Great Valley, one in the carbonates and one in the shales. These strike parallel drainages flow into one of the major rivers that transversly cut the Great Valley; the James, Potomac, Susquehanna and Delaware Rivers. Using several different methodological approaches; a field study, extraction of whole basin metrics from digital elevation models and longitudinal profiling, this study has reached several general conclusions about the landscape evolution of the Great Valley. One, upland gravel deposits do not indicate watershed expansion. Two, channel metrics suggest systems in disequilibrium that are sluggishly connected to changes in base level. Three, the two southernmost basins in the study, between the James and Potomac Rivers, show higher longitudinal profile modeling values than the other basins in the study. Four, ultimately, longitudinal profiling in this low slope environment proved to be insensitive.