FLOODPLAIN GEOMORPHOLOGY, FLOOD MAGNITUDES, AND FLOOD REMOTE SENSING

Many river floodplains are created primarily by non-flood processes such as lateral channel migration. Over geologic time, river valleys are widened and floodplain depositional landforms created. The resulting alluvial plains are subject to varying flood inundation risk for the same routed discharge. Such risk depends on many factors independent of discharge, such as surface elevations, local river channel conveyance capacities, alluvium permeability, and the presence or absence of natural and artificial levees. Flood hydrology analyzes gaging station-derived measurements of previous peak discharges in order to estimate probable future durations, magnitudes, and frequencies of flood-producing discharge events. In contrast, the spatial distribution of these discharges (where and how the water is stored or transported across the complex alluvial landscape) is normally modeled or estimated rather than observed. Fortunately, remote sensing from orbital platforms is today presenting the hydrological and geomorphological communities with entirely new but highly relevant data: detailed satellite imaging, at particular moments in time, of the progress of floodplain inundation. When such data are archived and data for new events are obtained, the relative magnitudes of floodplain inundation for a series of floods can be quantitatively compared. Inundation flood magnitudes can also be calibrated to the relevant series of measured peak discharges if a gaging station record is available. The combined inundation magnitude and water discharge information forms a more complete and useful description of a river reach's flood history than discharge information alone.