Articles | Volume 4, issue 1
Earth Surf. Dynam., 4, 273–283, 2016
Earth Surf. Dynam., 4, 273–283, 2016

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 Métivier1, Olivier Devauchelle1, Hugo Chauvet1, Eric Lajeunesse1, Patrick Meunier2, Koen Blanckaert3, Peter Ashmore4, Zhi Zhang5, Yuting Fan6, Youcun Liu7, Zhibao Dong5, and Baisheng Ye5,† François Métivier et al.
  • 1Institut de physique du globe de Paris – Sorbonne Paris Cité, Université Paris Diderot, CNRS – UMR7154, 1 rue Jussieu, 75238 Paris CEDEX 05, France
  • 2Département de Géologie, CNRS – UMR8538, Ecole Normale Supérieure, 24 rue Lhomond, 75005 Paris, France
  • 3Research center for Eco-environmental sciences, Chinese Academy of sciences, Beijing, P. R. China
  • 4Department of Geography, Social Science Centre Rm 2322, Western University, London, Ontario, Canada
  • 5The States Key laboratory of Cryospheric Science, Cold and Arid Region Environmental and Engineering and Research Institute, Chinese Academy of Sciences, 260 Donggang west road, Lanzhou, China
  • 6Xinjiang Institute of Ecology and geography, Chinese Academy of Sciences, Urumqi, P. R. China
  • 7Key Laboratory of Water Environment and Resource, Tianjin Normal University, 393 Binshui west road, Tianjin 300387, China
  • deceased

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.