Alvin Anderson Award Ceremony:
Award Winner: Gerald Salter, PhD Student in Earth Sciences (advisor Chris Paola)
Keynote Speaker: Jeff Nittrouer, Assistant Professor in Earth, Environmental, and Engineering at Rice University
Sedimentary dispersal systems with fine-grained (10-1000 mm) beds are common and societally important, building floodplains and deltas, and shaping coastlines where much of humankind lives. Yet the physics of sediment movement within these systems remains poorly constrained. For example, sediment transport data for the best-documented, fine-grained river worldwide, the Yellow River of China, demonstrate that well-accepted transport relations under-predict sediment flux by an order of magnitude. In this lecture, a theoretical framework, bolstered by field observations, is developed to demonstrate that the Yellow River tends toward upper-stage plane bed, yielding minimal form drag, thus markedly enhancing sediment transport efficiency. A new physically-based formulation is developed, which demonstrates a remarkably sensitive dependence on grain size within a certain narrow range (100-150 mm). To further explore this finding, a comprehensive sediment load database for fine-grained channels, ranging from small experimental flumes to mega rivers, is analyzed. It is determined that two distinct transport phases exist, separated by a discontinuous transition whereby sediment flux differs up to 100-fold in response to slight grain size changes near the sand-silt border. In situ measurements of sediment flux from the Yellow River validate this behavior and demonstrate how transport systems with bed material straddling the sand-silt border may transition between states of high or low efficiency, with unintended enhancement or suppression of river flooding.