Modern Coastal Plain drainage basins are complex plumbing systems that are the cumulative product of intimate inter-relationships between natural fluvial processes responding to dramatic Quaternary climatic and sea-level fluctuations and the lithology and geometry of the underlying geologic framework. The Waccamaw River in southeastern NC and Tar River in northeastern NC will be used to demonstrate the late Quaternary history and the Cretaceous controls upon modern riverine geomorphology and hydrology. The trunk streams consist of a series of riverine segments that are uniquely different from each other and have effected the hydrologic dynamics of each segment during its evolution through the Quaternary glacial and interglacial episodes. The riverine segments are defined by three sets of variables. 1) The underlying geologic framework defines the geomorphology and composition of both the paleo- and modern-channel and floodplain systems of both the trunk and tributary streams within each riverine segment. 2) Location of each riverine segment along the stream gradient relative to sea level determines the degree of interplay with the estuarine dynamics at two temporal scales: annual to individual storm events (i.e., the 1999 flood) and millennial to decadal scale. 3) Fluctuations in climate and sea level associated with Quaternary glaciation and deglaciation produced complex patterns of erosional incisement and sediment deposition that occur as partially preserved remnants within the modern drainage system. Consequently, the Coastal Plain portion of the drainage basins do not consist of simple fluvial types, but rather are complex rivers resulting from a rapidly changing climatic and sea-level history and highly variable underlying geologic framework. This inheritance dictates the geomorphologic, ecological, and hydrodynamic characteristics; should determine the resulting human land utilization practices; and will dramatically affect the flooding consequences.