The Earth’s surface is a patchwork of geological formations, shaped over deep time by the journeys of air, water, and ice. These forces erode, transport, and deposit the materials that form landscapes, and understanding the processes of sediment transport is central to understanding the behavior of our planet. Here Wainwright et al. look at the conventional definitions of sediment transport capacity—the total amount of sediment a fluid is able to carry—and how they compare with real-life observations.
The researchers used a critical realist approach, which requires that scientific investigations have concrete mechanisms to manipulate, as opposed to simple observation of cause and effect in order to decipher meaning. They began by tracing the concept of sediment transport capacity to its roots, in G. K. Gilbert’s 1877 Report on the Geology of the Henry Mountains. In it, Gilbert describes an increase in the ability of a river to transport sediment due to increases in stream flow and slope. The relationship between these features is echoed in later literature in various ways—and the researchers find that even modern sources use different terminology to describe transport capacity.
The team identified three problems with this straightforward view of the relationship between flow power and transport capacity. First, when a fluid picks up sediment, the nature of the flow itself is changed. Second, the movement of sediment affects the substrata, which also changes the nature of the flow. Finally, the relationship between transport capacity, flow strength, and slope does not stay consistent across scales. A river carrying boulders down a steep mountainside behaves differently than a mudflow picking up clay particles.
Because of these challenges, the researchers emphasize the need for new theories of sediment transport in order to better reflect the behavior of real geomorphic systems. A new theoretical approach could be a strong foundation for practical applications for predicting and managing our planet’s patchwork landscapes. (Reviews of Geophysics, doi:10.1002/2014RG000474, 2015)
—Lily Strelich, Freelance Writer
Citation: Strelich, L. (2016), Sediment transport capacity carries many meanings, Eos, 97, doi:10.1029/2016EO045341. Published on 5 February 2016.