B2B  |  Feedback  |  COSIS.net on Facebook COSIS.net News on Twitter


Lost Login Data?

Science News


From article

Source article

Journal of Geophysical Research

Published By

Dr. Dick van der Wateren

Tags

Rivers & Streams, Geological Modeling, meander


Follow @COSISnews on Twitter


For the first time: Meanders in the Lab

07.10.2012, Age: 2020 days

A team from Utrecht University in the Netherlands succeeded for the first time to produce an actively meandering river in a flume experiment. While it is relatively easy to produce braided channels in the lab, meandering streams are notoriously hard to produce. The Utrecht team's innovation includes a special sand mixture and a new way of feeding the upper end of the model river.

The problem with modelling meandering rivers in the lab is that the sediment normally used in flume experiments lacks cohesion. This invariably results in braided channel patterns, which can be even simply produced on the beach or in the backyard. Too much cohesion of the sediment, however, results in a river that indeed meanders, but remains fixed and tends to cut down into the substrate. Dynamic meanders move downstream, producing point bars, meander cutoffs and all the other familiar features of a lowland floodplain.

First author Wout van Dijk, his colleague Wietse van de Lageweg and their supervisor Maarten Kleinhans succeeded in producing exactly these features using a clever mixture of fine sand and silica flour with just the right amount of cohesion. Their other innovation was to introduce channel perturbations by slowly moving the upstream feeding point sideways.

Abstract

Braided rivers are relatively simple to produce in the laboratory, whereas dynamic meandering rivers have not been sustained beyond initial bend formation. Meandering is theoretically explained by bend instability growing from planimetric perturbation, which convects downstream. In this study, we experimentally tested the importance of upstream perturbation and chute cutoff development in the evolution and dynamics of a meandering channel pattern. The initial straight channel had a transversely moving upstream inlet point and silt-sized silica flour was added to the sediment feed to allow floodplain formation. We obtained a dynamic meandering river with scroll bars. Bend growth was alternated by chute cutoffs that formed across the point bars. Meandering was maintained as one channel was disconnected by a plug bar. The curvature at the chute bifurcation transported sediment and build a new floodplain, while the other channel widens. At the end of the experiment, the fluvial plain exhibited a meandering channel, point bars, chutes and abandoned and partially filled channels with a slightly cohesive floodplain surface similar to natural meandering gravel bed rivers. We conclude that the necessary and sufficient conditions for dynamic meandering gravel bed river are a sustained dynamic upstream perturbation and floodplain formation.

W. M. van Dijk, W. I. van de Lageweg, and M. G. Kleinhans. Experimental meandering river with chute cutoffs. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, F03023, 18 PP., 2012. doi:10.1029/2011JF002314


Twitter Facebook LinkedIn Google Bookmarks Linkarena Newsvine Oneview Stumbleupon Windows Live Yigg

Add Comment (login required)