ABSTRACT
Floodplains play a fundamental role in landscape evolution and response to forcings, from rapid flood events to carbon storage. At the same time, floodplains are among the most vulnerable environments on the surface of the Earth. While often believed in contact with their rivers via overbank flow during floods only, recent research has highlighted the existence of a continuum of surface water connectivity between these two environments and the need for quantifying the mechanisms of hydrological connectivity and its implications for the delivery of solids and solutes onto the floodplain. Here we study the Trinity River, a meandering river located in Texas, as a natural laboratory. The river extends from a quasi-normal reach to a backwater-dominated reach towards the coast. Using lidar and bathymetric data, we apply a hydrodynamic model over the domain and validate our results with field observations of water level and flow velocity collected in levee channels during several months. Our results show that levee topography and vegetation emerge as primary controls of the channel-floodplain hydrological connectivity. We also find that the style of water flow over the floodplain is a function of stage and that the directionality of the water movement impacts the delivery of sediment to the floodplain. The results point at a range of channel-floodplain connectivity mechanisms and suggest that flood duration may be controlling the ability of the river to erode its banks.
