Effects of River Valley Segment Sequencing on Floodplain Hydroperiods

River valleys rank among the most biophysically complex and species-rich ecosystems in any landscape. Although local floodplain morphology is known to impact annual and event-specific hydroperiods, understanding of flood hydrology is typically based on model simulations that route catchment water contributions through hydraulic constraints imposed by local channels and valleys, and do not explicitly consider network context. To investigate the impact of valley sequencing on floodplain hydroperiods, novel approaches were first developed in order to characterize the morphology of south-central Indiana's White River valley. Utilizing this information, numerical simulations of both hypothetical hydraulic constraints and empirical characterizations of valley segments and flood hydrographs were developed. Strong path-dependent effects were found demonstrating that the sequence in which rivers encounter different valley segment morphology can dramatically alter local water levels, leading to strong spatial and temporal variation in flooding risk, their intensity, and time of inundation for a given flood pulse. Because a systematic approach was developed for identifying strong variations in expected flood regime throughout the river valley, our findings have particular relevance for conservation and restoration efforts focused on river valley biodiversity and ecosystem services, including floodplain biogeochemistry and greenhouse gases production in riparian systems