Flume Experiments of Response of a Delta Profile to Temporary Waxing Discharge : The Case of Silt-Sized Diatomaceous Earth(<Featured Articles>Turkey-Japan Joint Conference on Geomorphology)

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The delta profile changes corresponding to hydraulic condition, such as flow discharge, sediment supply rates and sediment type. In order to examine silty delta profiles under temporary waxing flows, we conducted experiments in which a silty delta was developed under several patterns of hydrograph. The findings are as follows. (1) When the flow discharge increases, sedimentary process of a delta is determined by increase rates and there occurs aggradation, backstepping, and progradation respectively as the rate becomes large. (2) If the flow was kept at high discharge for a while before waning, the delta prograded forming a steep foreset slope, regardless of increasing rates. (3) In the phase of decrease of flow discharge, under slowly waning flow, the delta developed with backstepping followed by aggradation when the topset was quasi-equilibrium state, but prograded when the condition of the topset was quasi-equilibrium state, while under fast waning flow, a sedimentary process of a delta was always aggradation on the topset regardless of the increase rate of discharge at the previous phase. It is expected that applying these findings contribute to estimating unsteady hydraulic conditions like floods from geologic records of a silty delta.
日本地形学連合の論文
2011-04-25