CSDMS 2017 annual meeting Harrison Gray

From CSDMS
Presentation provided during CSDMS annual meeting 2017

Traveling at the speed of light: luminescence as a means to quantify fluvial sediment transport rates
Harrison Gray
University of Colorado
Sediment transport in rivers is a key parameter in landscape evolution, fluvial sedimentation, and river engineering. In particular, information on the time-averaged virtual velocity and the channel/floodplain exchange rate of sediment is extremely useful for quantifying long-term sediment transport dynamics. This data is expensive and time-consuming to obtain. A potential solution is to use luminescence, a property of matter normally used for dating. I develop a model based on conservation of energy and sediment mass to explain the patterns of luminescence in river channel sediment. The parameters from the model can then be used to estimate the time-averaged virtual velocity, characteristic transport lengthscales, storage timescales, and floodplain exchange rates of fine sand-sized sediment in a fluvial system. I show that this model can accurately reproduce the luminescence observed in previously published field measurements. I test these predictions in three rivers where the sediment transport information is well known: the South River and Difficult Run in Virginia, and Linganore Creek in Maryland. Each of these rivers tests key predictions of the model with the South River having favorable conditions, Difficult Run having large amounts of human influence, and Linganore Creek switching from alluvial to bedrock and vice versa along its course. In the South River, the model successfully reproduces the virtual-velocity and exchange rates from previously published data. In Difficult Run, we find that the influx of sediment from human development obfuscates the model-predicted pattern as expected. In Linganore Creek, the shift from alluvial covered to bedrock and back produces a change in the luminescence consistent with the predictions made by the model. From these results, I conclude that when model assumptions are upheld, luminescence can provide a useful method to obtain sediment transport information. This finding, coupled with the advent of portable luminescence technology, opens the door for rapid and inexpensive collection of long-term sediment transport data.


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