Modern Fluvial Crevasse-Splay Deposits

:Sedimentary Records of the August 2022 Flooding of Nakasato River in Tsugaru Plain

Abstract

Heavy rainfall triggered by a quasi-stationary front occurred on 8-13 August 2022, leading to flooding of the Nakasato River in Tsugaru Plain, northern east Japan. Dike breaks along the river resulted in the deposition of a large amount of sediment, so-called crevasse-splay deposits, on the plain.

Crevasse splay deposits are mainly composed of fine to medium sand with gravels and can be divided into the following four units： Unit 1, gravel layer covering artificial soil layer; Unit 2, blue-grey fine sand; Unit 3 light brown medium to coarse sand and mud mixtures with mud clasts and gravel, indicating traction-carpet stratification; Unit 4 light yellow medium sand including erosional basal contact. The difference between four units correspond to the changes in flow condition during the flooding.