RII Track-4: Improving Understanding of River Flood Dynamics by Relating Flow and Sediment Movement to Shapes of River Dunes in three dimensions

Much of the world’s population and commerce exist along river corridors. The sustainability of human settlements and the impacts they have on their environments are inextricably tied to river flood and sediment dynamics. Bedforms, migrating mounds of sand such as ripples and dunes, are a primary feature observed on the bottom of dynamic river systems.

Their geometries and motions are closely tied to river flow and sediment transport and each one influences the other in complex feedback loops. Direct measurement of all components of these coupled feedbacks is challenging in modern rivers and difficult to interpret in their ancient sedimentary deposits, hindering complete, understanding over long timescales.

Over a century of study has attempted to relate bedform shapes, motions, and ancient deposits to the flow and sediment transport conditions that form them. Much of this effort has focused on two-dimensional frameworks. This project establishes a new set of experimental and field techniques in a collaborative setting for collecting coupled measurements of flow, sediment transport, and bedform evolution in three dimensions.

In so doing, this work will expand the physical and intellectual capacity of the University of New Orleans to address problems in sediment transport research that extend beyond the scope of this project. This expanded capacity will broaden participation and serve the diverse university community as well as the southeastern region by establishing a highly capable sediment transport facility with state-of-the-art methods at a highly diverse public university in New Orleans.

Bedforms are a primary observable feature of sediment transport systems. Their geometries and kinematics (motions) are closely coupled to the dynamics (forces) of flow and sediment transport. As such, bedforms and their stratal elements are key to understanding river conditions, past and present.

Flow and sediment transport conditions in sand-bed alluvial systems are tightly coupled to the kinematics of bedforms. Bedforms serve to transport bed material sediment, and their forms extract momentum from the flow in alluvial river systems. Understanding their geometry and behavior can inform models that evaluate bed material flux and shear stress partitioning in modern river systems, as well as enhance interpretation of ancient fluvial strata.

This project seeks to build capacity, establish lab protocols, and collect data to address three independent hypotheses: First, that cross-stream, relative to downstream, bedload particle excursion length and velocity increase with increasing turbulent energetics of the flow; second, that increasing probabilities of cross-stream particle collisions enable the establishment of three-dimensionality of bedform topography; and third, that turbulent characteristics of flow, namely shear velocity, can be inverted from three-dimensionality of bedforms and the curvature of cross set bounding surfaces in stratigraphy. A complete assessment of these hypotheses will enhance the ability to forward model bedform geometries and kinematics based on flow and sediment transport conditions.

This will bolster inverse models used to quantitatively interpret past sediment transport and flow conditions based on observations of stratigraphy. In collaboration with researchers at the University of California, Santa Barbara, this fellowship will address both regionally and nationally relevant problems of river flood dynamics.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.