Journal of Geophysical Research: Earth Surface
© 2014 American Geophysical Union
Impact Factor: 3.44
ISI Journal Citation Reports © Ranking: 2013: 24/173 (Geosciences Multidisciplinary)
Online ISSN: 2169-9011
Associated Title(s): Journal of Geophysical Research
Area-based approach improves global sediment discharge modeling
By approaching the challenge of calculating global sediment discharge rates from a new angle, Pelletier (2012) developed a model that outperforms many existing simulations while minimizing the number of free parameters. Knowing how sediment is transported by the world's rivers is a key factor in understanding how landscapes change over time, with important consequences for agricultural viability, ecological health, and soil properties. Traditionally, the majority of discharge models calculate sediment redistribution at the watershed or drainage basin scale, using watershed average values of the physical properties known to affect sediment transport. The author's model, on the other hand, partitions the planet into sections that are 5 arc min wide-roughly 10 km across at the equator and smaller at higher latitudes. This decision to use an area-based grid rather than drainage basin averages allows for an improved representation of small-scale processes that are often washed out at the watershed scale. Drawing on decades of published research into the effects of various physical parameters on sediment discharge rates, the author's model breaks the calculation for the amount of sediment flowing through each grid square into two distinct steps. First, the model uses observations of leaf area index, temperature, rainfall rate, soil type, and topographic variables to calculate how much sediment will become available through erosion. Then, it calculates the balance between the slope, water depth and flow rate, and sediment properties to estimate how much of the available suspended sediment will be carried from each pixel. Compared against an observational database representing 128 rivers, the model's calculated long-term average sediment discharge rates matched observations reasonably well.