Gravel-bedded rivers, such as the one pictured here in Yellowstone National Park, are major features of some of the world’s most diverse ecosystems. Understanding rivers’ bankfull geometry—the shape of a river during the stage just before flooding— is an important key to flood management in these regions.
Typical models for predicting a gravel-bedded river’s geometry rely on a simple assumption: that the flowing water does not generate enough shear stress to move average-sized sediment until the river reaches its bankfull stage. If that assumption holds true, the stable “armor” layer of gravel that makes up the riverbed only shifts once every few years. However, a new paper by Allison Pfeiffer, a graduate student at the University of California, Santa Cruz, shows that many rivers generate much larger amounts of shear stress than standard models predict. Pfeiffer concludes that the amount of sediment being fed into a river is a major...
