Morphodynamics of large anabranching rivers: the case of the Madeira River, Brazil

Authors: Xiwei Guo*, Syracuse University, Edgardo Latrubesse, The University of Texas at Austin
Topics: Geomorphology, Physical Geography
Keywords: Large rivers, Fluvial geomorphology, morphodynamics, Amazon
Session Type: Paper
Day: 4/12/2018
Start / End Time: 5:20 PM / 7:00 PM
Room: Balcony K, Marriott, River Tower Elevators, 4th Floor
Presentation File: No File Uploaded

Anabranching channels are the dominant channel pattern of large rivers worldwide. Given the limited understanding on the form and process of anabranching channels, this study focuses on the elucidation of the morphodynamics of a 150-km channel segment of the Madeira River, the largest tributary of the Amazon River with anabranching channels. The studied river channels are divided into three reaches: 1) Box-shaped channels with upstream and downstream anabranching structures; 2) A pseudo-meander with a downstream anabranching structure; 3) A single-threaded straight channel with a downstream anabranching structure. The analysis of the spatial-temporal channel changes of the three reaches since 1985 demonstrates the slow process of channel lateral migration and the stability of large anabranching rivers. Besides three sites with special geomorphic settings, more than 87% of the channel did not have lateral migration. The area being eroded and deposited stayed relatively equivalent until after 2010, in which channel incision (erosion) significantly exceeded the amount of deposition, possibly due to the closure of two large dams upstream. Channel morphology vary largely among different channel structures, while geologic controls play an important role in a number of places that significantly alters channel behaviors. For most part of the channels, the width stays constant with increasing discharge, which may imply limited channel-floodplain interactions. The hydro-geomorphological features of two anabranching structures, one in reach 2 and one in reach 3, each demonstrates avulsion (erosion-triggered) and in-channel accretion (deposition-triggered), which are the two mechanisms of anabranching formation.

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