Investigating hysteresis in floodplain dynamics of lakes in the middle St. Johns River using Sentinel-1 SAR imagery

Floodplain dynamics are often complex, with hysteresis potentially affecting the temporal relationship between river gauge readings and flood extent during flood directions. This study leverages Sentinel-1 synthetic aperture radar (SAR) imagery to map flood extent in the Middle St. Johns River Lake floodplains and examine the presence of hysteresis during flood events. SAR scenes corresponding to river gauge readings were analyzed from the rising and falling limbs of a flood hydrograph. By comparing these flood maps, we assess differences in inundated areas at equivalent water levels during each stage of the flood event. The findings aim to enhance flood monitoring systems by improving flood extent mapping throughout changing water levels, which is crucial for accurate flood forecasting and effective response planning. Our results indicate that hysteresis in this region is primarily governed by topography and channel connectivity, where the floodplain geomorphology and tributary drainage to lakes lead to acceleration in drainage from the floodplain to the lake during the falling limb when comparing inundation extent to the rising limb at similar water levels. Among the three floodplains studied, Lake Jesup displayed the largest range of degrees of hysteresis (-0.03 to 0.32), followed by Lake Monroe (0.03 to 0.25) and Lake Harney (0.02 to 0.22). The differing ranges of degrees of hysteresis are attributed to unique lake-river connectivity and floodplain topography.