Flume experiments in which the silty deltas were developed under unsteady flows were conducted.We examined several increasing and decrease rates of flows.Results showed that sedimentary processes of a delta were aggradation at high increase rates of discharge,backstepping at middle rates,and progradation at low rates.In the phase of decreasing flow,there was hysteresis in the development process.Even if the decrease rate was the same,the process of topographic change was different according to the previous state of the delta shape.Besides we found that the development processes related with the sediment balance(erosion-sedimentation) on the topset bed that was quasi-equilibrium state at low increase rates of flow discharge,but was non-equilibrium state at high increase rates of discharge. Flume experiments in which the silty deltas were developed under unsteady flows were conducted. We registered several increases and decrease rates of flows.Results showed that sedimentary processes of a delta were aggradation at high increase rates of discharge, backstepping at middle rates, and progradation at low rates.In the phase of decreasing flow, there was hysteresis in the development process. Even if the decrease rate was the same, the process of topographic change was different according to the previous state of the delta shape.Besides we found that the development processes related with the sediment balance (erosion-sedimentation) on the topset bed that was quasi-equilibrium state at low increase rates of flow discharge, but was non-equilibrium state at high increase rates of discharge.