Collaborative Research: NSF/EAR-BSF: Coupled Sand and Clay Motion, Bed Morphodynamics, and Porewater Exchange

Clay-sand mixtures occur ubiquitously in freshwater, estuarine, and marine environments, and the transport and mixing of these sediments regulate many critical system attributes including bottom topography, sediment hydrogeological properties, and habitat conditions. However, little is known on how coupled clay-sand-porewater dynamics control overall behavior of systems with mixed sand/mud deposits. This project aims to show that clay-sand-porewater coupling follows a regular, fundamental, and ubiquitous set of processes: advective delivery of suspended clay into sand beds, accumulation of fine particle deposits in the beds, and feedbacks resulting from clay filling pore spaces and bridging sand grains. Experiments and theoretical analysis will be performed collaboratively between U.S. and Israeli institutions via parallel experimentation, regular videoconferences, and international exchanges of project staff. Project results will directly support hands-on demonstrations and authentic and engaging geosciences learning experiences for junior-high and high-school students. Educational programs will be conducted both at project universities and in K-12 classrooms. The overarching hypothesis of this project is that clay, sand and porewater transport are coupled such that motion of all three constituents regulates bed morphodynamics, and, conversely, bed morphodynamics controls the immobilization, retention, and remobilization of both sediments and porewater. The work is organized to achieve three objectives: 1. Observe coupling between clay and sand transport dynamics and bed morphodynamics in laboratory experiments under steady and unsteady flow conditions, and with varying degrees of particle cohesion. 2. Observe coupling between porewater flows and clay-sand dynamics, including effects of porewater upwelling and downwelling on sediment transport, and feedbacks between sediment deposition patterns and porewater flow. 3. Develop theory relating statistics of motion to particle residence time and transit time distributions, bedform morphodynamics, ensemble sediment fluxes, porewater exchange fluxes, and frequencies and magnitudes of particle resuspension. Primary intellectual contributions of this work are: 1. Paradigm-challenging theory and experiments on coupling of washload and bedload transport, which co-occur ubiquitously but are currently treated independently. 2. Highly detailed laboratory investigation of the effects of salinity, clay intrusion, and porewater flux on sand bed morphodynamics. 3. Evaluation of nonstationarity and hysteresis in clay-sand morphodynamics under unsteady flow forcing and gaining/losing porewater conditions. 4. Fundamental stochastic theory for coupled clay-sand-porewater dynamics. 5. Model for upscaling sediment and porewater dynamics in mixed sand/mud systems. This international collaborative proposal provides experimental data and stochastic theory necessary to understand clay-sand dynamics that occur ubiquitously in lowland rivers, estuaries, deltas, and continental shelfs. Primary broader impacts of this work are: 1. Acquisition and dissemination of ultra-high-resolution datasets for validation of integrated earth-surface and marine morphodynamic models. 2. Development of transferrable theory for assessing upscaled outcomes of coupled clay-sand morphodynamics in rivers, estuaries, and the continental shelf. 3. Mechanistic theory for anomalous diffusion in sediment-water systems directly applicable to sediment biogeochemistry, early diagenesis, and contaminant dynamics. 4. Project results dire