Articles | Volume 4, issue 1
Research article
22 Mar 2016
Research article |  | 22 Mar 2016

Geometry of meandering and braided gravel-bed threads from the Bayanbulak Grassland, Tianshan, P. R. China

François Métivier, Olivier Devauchelle, Hugo Chauvet, Eric Lajeunesse, Patrick Meunier, Koen Blanckaert, Peter Ashmore, Zhi Zhang, Yuting Fan, Youcun Liu, Zhibao Dong, and Baisheng Ye

Abstract. The Bayanbulak Grassland, Tianshan, P. R. China, is located in an intramontane sedimentary basin where meandering and braided gravel-bed rivers coexist under the same climatic and geological settings. We report and compare measurements of the discharge, width, depth, slope and grain size of individual threads from these braided and meandering rivers. Both types of threads share statistically indistinguishable regime relations. Their depths and slopes compare well with the threshold theory, but they are wider than predicted by this theory. These findings are reminiscent of previous observations from similar gravel-bed rivers. Using the scaling laws of the threshold theory, we detrend our data with respect to discharge to produce a homogeneous statistical ensemble of width, depth and slope measurements. The statistical distributions of these dimensionless quantities are similar for braided and meandering threads. This suggests that a braided river is a collection of intertwined threads, which individually resemble those of meandering rivers. Given the environmental conditions in Bayanbulak, we furthermore hypothesize that bedload transport causes the threads to be wider than predicted by the threshold theory.

Short summary
In meandering rivers, flow and sediments are carried in a single thread whereas in braided rivers they are carried through numerous threads. The geometry of single-thread follows scaling relationships with discharge. The most famous of these, "Lacey's law", states that a river's width scales with the square root of its discharge. We here show that threads from braided rivers also accord with Lacey's law, and that the geometry of meandering and braided threads cannot be differenciated.