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Experimental evaluation for peak and temporal changes in debris-flow initiation processes
Itoh, Takahiro Ikeda, Akihiko Mizuyama, Takahisa
Itoh, Takahiro
Ikeda, Akihiko
Mizuyama, Takahisa
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2019
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Abstract
Saturated sediment water mixture flow can move as landslide if the vertical sediment concentration is constant and the value takes a maximum sediment concentration, c*, which is sediment concentration in the non-flowing layer in sediment deposition. The flow is debris flow over the rigid bed and the flow can change as debris flow with vertical sediment concentration distribution if the saturated flow reaches downstream reach, where bed inclination is around 17 to 18 degrees. The thinking proposes that it is important to know transition process in between saturated landslide and debris flows in evaluating peak and temporal changes of debris flows in initiation processes for debris-flow mitigation in planning and design of sabo dam, because the transition process can be explained by a relation between bed slope and depth-averaged sediment concentration (e.g., Takahashi 1991). In present study, important knowledge for estimating peak discharge is discussed using experimental data obtained by present flume tests. Flume tests are carried out using prismatic open channel which is set 22 degrees and around 18 degrees at downstream end. Sediment is deposited parallelly to the flume bed and water is supplied steady at upstream end, and the transition of between saturated landslide to debris flow is produced. Two kinds of sediment deposition depth and length are specified in the present tests, and temporal changes of debris flow are measured using side view of digital video camera and debris-flow runoff at downstream end of the flume. The data shows that peak discharge rate of debris flow depends on sediment volume during debris-flow running from the up to the downstream reach, and that entrained sediment volume by a debris flow will be determined by erosion capacity during a debris-flow surge.
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