Annualmeeting:2017 CSDMS meeting-125

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Intermittency, Sediment Advection Length Distribution, and Delta Island Development.

Max Daniller-Varghese, University of Texas at Austin Austin Texas, United States. maxdv@utexas.edu
Wonsuck Kim, University of Texas at Austin Austin Texas, United States. delta@jsg.utexas.edu
David Mohrig, University of Texas at Austin Austin Texas, United States. mohrig@jsg.utexas.edu


[[Image:|300px|right|link=File:]]To better understand large-scale delta-network responses to fluctuating discharge, we focused on the evolution of a single channel-island node within a delta network. Using the Surface Transport and Earth-surface Processes (STEP) basin, we were able to construct and observe the evolution of mouth-bar systems and subsequent flow bifurcation around an individual island in transport-limited, turbulent conditions. Overhead time-lapse images, laser-altimetry scans, and a low-cost particle tracking velocimetry system allow us to characterize the flow and depositional evolution of our experimental islands. Two alternating discharges that model flood and interflood transport (6 l/s, 0.355 l/s) with uniform sediment (170 microns) were used to create two characteristic sediment advective lengths. Floods transport sediment in full suspension (P_flood at inlet = 0.16), while interfloods transport sediment as bedload (P_interflood at inlet = 2.7). The consequent deposits are distal steep deposits from floods raining sediment out of suspension, and proximal low-angle, leveed deposits from interfloods laterally advecting sediment and floods remobilizing sediment down-system. By varying the frequency of floods (one every 20s-20 mins) while keeping sediment and water mass constant across experiments, we are able to control the time and spatial organization of these two deposit types and examine the effect on bifurcation length and bifurcation incidence time. While the deposits are initially spatially segregated, as the interflood deposit and flood deposit accumulate sediment over time, the interflood deposit encroaches onto the flood deposit. Flow routes from the interflood deposit to the flood deposit and bifurcates because of a preferential slope gradient around the distal deposit. Rather than a single hydrodynamic condition dictating the location of bifurcation, the length to a bifurcation can be described by the intersection of multiple distributions of topographies from the variable flow of solids.