Geomorphology of the Congaree River Floodplain: Implications for the Inundation Continuum

Floodplain inundation has been viewed as a type of binary process set by the relative elevation between river stage and levee crest. However, recent reports in the literature show that this perception may have limited applicability. In particular, through-bank channels, conduits that cross the main river levees or banks, facilitate conditions for an "inundation continuum," or inundation for a range of sub-bankfull flows. Moreover, through-bank channels and their networks provide a direct hydraulic connection between the main river and the floodplain interior. We analyzed through-bank channel structure and floodplain topography and compared them to river surface elevation to provide greater insight on floodplain inundation processes. Results show that well-developed levees with through-bank channels facilitate frequent through-bank inundation. Where levees are poorly developed, floodplain inundation occurs by overbank flow. Therefore, for a given discharge through-bank and overbank inundation may occur simultaneously. For the Congaree River floodplain, we infer that this dichotomy of inundation processes leads to temporally and spatially complex inundation flow paths for a given river stage. Further, our analyses reveal that the inundation continuum concept should be considered in the context of having vertical, longitudinal, lateral, and temporal components.