Traveling at the Speed of Light: Using Luminescence to Estimate Sediment Transport Rates

Abstract:

Most people live near a river which is actively transporting sediment, and for many, a change in sediment
dynamics can greatly affect livelihoods. A better understanding of sediment transport mechanics is critical
for improving our coexistence with river systems, especially in the face of a changing climate. However,
there are currently few ways in which to measure and quantify sediment transport rates in rivers. Tracer
experiments are laborious and time consuming, sediment traps are diffcult to construct without altering
flow dynamics, and reservoir infill methods require long observation timescales. The difficulty in obtaining
these data has precluded its collection on a large scale and is limiting progress within the field. A method
that circumvents these issues would be invaluable.
We present a new means to estimate the sediment transport rates of rivers using luminescence, a property
of minerals used by the geoscience community for geochronology. Luminescence is a concentration of energy
stored within the crystal lattice of minerals that can be removed by sunlight and restored by natural radiation.
We use a continuity equation to describe the change in luminescence equivalent doses as a function of
downstream distance and compare againsteld data. Our model can reproduce field measurements from
two rivers with varying sediment transport styles for fine sand (180-200 µm). The field data and modeling
results reveal two patterns of interest for both rivers: an upstream region showing a gradual decline in
luminescence followed by a region where the luminescence is approximately constant. When the observed
luminescence is spatially constant, this represents a balance between bleaching and in flux of unbleached
sediment. The information obtained from applying the model to these regions can be used to estimate
sediment velocity and erosion and deposition of unbleached and bleached grains. Potential exists to extend
the model to bedload transport.