Application of a Luminescence‐Based Sediment Transport Model

Abstract

Quantifying the transport history of sand is a challenging but important goal in geomorphology. In this paper, we take a simple idea that luminescence is bleached during transport and regenerates during storage, and use this as a basis to re‐envision luminescence as a sediment tracer. We apply a mathematical model describing luminescence through an idealized channel and reservoir system and then compare this idealized model to real rivers to see if luminescence can reproduce known sediment transport data. We provide results from application of this luminescence method in three rivers from the mid‐Atlantic region of the United States. This method appears promising. However, as a river system diverges from idealized conditions of the mathematical model, the luminescence data diverge from model predictions. We suggest that spatial variation in the delivery of sediment from hillslopes can be reflected in the channel sediment luminescence and that luminescence acts as a function of landscape dynamics.

Luminescence as a Sediment Tracer and Provenance Tool

“…Delivery of unbleached sediment can occur if a tributary is less effective in bleaching than the main channel, say due to enhanced sediment load (Gray et al, ; Li et al, ). Other examples include entrainment of unbleached sediment by river channel incision (Muñoz‐Salinas et al, ), lateral channel erosion due to river meander, and variability in soil erosion rates (Gray et al, ). Broadly, the spatial patterns of luminescence within a river system, or across river systems, may have the potential to give insights into flood dynamics (Knight & Evans, ) and into landscape dynamics (Muñoz‐Salinas, Castillo, Caballero, et al, ; Portenga et al, ).…”

“…There are a handful of new methods offering insight into sediment transport, yet many parameters are not fully constrained, and the field has not yet reached a “holy grail” of predicting bulk volumetric sediment fluxes with luminescence. First, McGuire and Rhodes (, ) and Gray et al (, ) have demonstrated the potential of using luminescence as a downstream tracer in fluvial sediment to quantify virtual velocities. However, important problems remain open for study.…”

“…Bleaching rates can vary by orders of magnitude depending on the light flux. The time needed to fully bleach a luminescence signal ranges from seconds in direct sunlight to months and significantly longer in turbid water (Gemmell, ; Gray et al, ). Bleaching can occur prior to transport, during transport (as for example when a grain is suspended in a fluid flow), and/or following deposition on a surface, where a stationary grain can receive prolonged sunlight exposure (Gray & Mahan, ).…”

“…In an idealized landscape with idealized luminescence, the bleaching rates are constant throughout, such that the luminescence lost per unit transport distance is a function of drainage area. In such a case, stream junctions deliver sediment with volume and luminescence proportional to the upstream drainage area and the theoretical result is a power‐law decrease in luminescence downstream (Gray et al, ; Gray et al, ). However, nature is heterogeneous and the downstream decrease can change to an increase if enough unbleached sediment is delivered to the channel relative to the current sediment load (Gray et al, ; McGuire & Rhodes, ).…”

“…The use of luminescence to directly quantify geomorphic processes is an important research frontier (Heimsath & Ehlers, ). The potential applications of luminescence are rapidly expanding to provide new quantitative insights into geomorphic processes such as exhumation using OSL (Herman et al, ) and TL (Biswas et al, ; Brown et al, ), soil mixing and transport (Furbish, Schumer, et al, ; Reimann et al, ), surface exposure (Sohbati et al, ) and surface erosion (Sohbati et al, ; Guralnik & Sohbati, ), source area weathering and erosion (Haddadchi et al, ; Sawakuchi et al, ), fluvial sediment transport (Gray et al, ; McGuire & Rhodes, ), and coastal sediment transport (Ahmed et al, ; Reimann et al, ). Luminescence can provide quantitative sediment transport data from source to sink (Figure ) including the identification of provenance (Figure ).…”