Journal of Geophysical Research: Earth Surface
© American Geophysical Union
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ISI Journal Citation Reports © Ranking: 2014: 19/175 (Geosciences Multidisciplinary)
Online ISSN: 2169-9011
Associated Title(s): Journal of Geophysical Research
Younger sediments more likely to be eroded by meandering rivers
The duration of the journey that an individual grain of sand takes as it bounces its way down the length of a river is incredibly difficult, if not impossible, to determine. Finding the answer to that question can be useful because the amount of time that sediment spends in a river can affect how pollutants or other materials move through the system. At the bulk scale, sediment balance measurements, comparing the inputs and outflows of sediment, can be used to help calculate how much sediment is moving through a waterway. Figuring out the storage time of particular grains is more difficult because in meandering rivers individual grains of sediment deposited along the banks may be subsequently eroded years or even millennia later—whenever the river meanders back to where the sediment was deposited. Being able to calculate the total trip times of particular bits of sediment, then, means being able to properly model this long-term deposition-storage mechanism.
Traditionally, researchers modeling sediment storage have assumed that rivers meander randomly, meaning that all deposited sediments are equally likely to be eroded. In a new study, however, Bradley and Tucker found that river meandering, and hence sediment erosion, follows a complex relationship such that, in general, sediments that had been in storage for less time were more likely to be eroded. Using a river meandering model they found that the age-erodibility relationship breaks into three groupings: in sediments that had been in storage for a few hundred to a few thousand years, grains were eroded equally; in sediments stored from a few thousand to tens of thousands of years, younger grains were more likely to be eroded; and in older sediments there was no clear trend.