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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Research
Vol. 93 (2023), No. 11. (November), Pages 825-839
https://doi.org/10.2110/jsr.2023.029

FLUME Previous HitEXPERIMENTSNext Hit IN THE DEVELOPMENT OF CREVASSE-SPLAY DEPOSITS: TRANSITION FROM ASYMMETRIC TO SYMMETRIC GEOMETRY

Taichi Kato, Masaki Yamada, Hajime Naruse, Yuichi Sakai

Abstract

Crevasse-splay deposits play an important role in the reconstruction of the magnitude of past flood events and in understanding the behavior of river systems. Despite the extensive studies conducted on the geometry and facies of crevasse-splay deposits, their spatiotemporal developmental processes have remained insufficiently understood. In this study, scaled flume Previous HitexperimentsNext Hit were conducted to study the relationship between the developmental processes of crevasse splays and their characteristics. An experimental flume was set up in a tank to simulate the 2019 Chikuma River flooding event in central Japan. To Previous HitmodelNext Hit the overbank flow, an opening was created on the side of the flume’s wall through which the flow flooded onto a horizontal acrylic plate. The sediment used in the Previous HitexperimentsNext Hit consisted of particles with grain sizes of approximately 0.3 and 0.1 mm, which were determined to be equivalent to bedload gravel and suspended sand in a real-scale river using dimensional analysis. The results of the Previous HitexperimentsTop revealed three important findings: 1) Crevasse-splay deposits initially developed an asymmetric shape extending downstream of the main river channel but gradually showed a symmetric geometry. The river mainstream initially influenced the direction of the inundation flow, but channel bifurcations after the deposition of the sediment piles later changed the geometry of splays into a more symmetric shape. 2) Crevasse-splay deposits developed in two distinct regions (proximal and distal splay), corresponding to sediment transport by bedload and suspended load, respectively. These two regions are commonly observed in the actual field scale. 3) The original overbank flow was a sheet flow without channels, which caused coarse-grained sediments to be spread over a wide area. Subsequently, the accumulation of coarse sands in the developed channel interiors resulted in the buildup of finer-grained sediments upstream of the proximal splay. Thus, the proximal splay deposits became slightly coarse downstream, whereas they rapidly became fine at the boundary with the distal splay. These findings indicate that the characteristics of crevasse-splay deposits vary with the landform’s development stage, thus providing a basis for interpreting their depositional facies.


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