Study On The Simulation Of Non-equilibrium Fluvial Processes

This paper studied the characteristics of the delayed response of the fluvial systemsaffected by different disturbance. A method for simulating non-equilibrium fluvialprocesses was developed based on the delayed response model and the analysis of theequilibrium state of fluvial systems. The long term evolution processes of the YellowRiver reaches and the North Fork Toutle River in the United States were simulatedusing the proposed method. This paper enhances our understanding of non-equilibriumfluvial processes and contributes to the development of the theory and methods withrespect to channel evolution.Based on the concept of river system, the disturbance of alluvial rivers is dividedinto the runoff and sediment conditions and the base-level change at the downstream.The potential equilibrium state of the fluvial system affected by both the two factorswas studied and a method was developed for calculating the equilibrium value of theaggradation and degradation volume of channel reaches.Xiaobeiganliu and the lower Weihe River are both affected by water discharge andsediment load and the variation of Tongguan elevation. It’s assumed that channelreaches in their potential equilibrium state, compared to the initial boundaries, have adeposition body in the shape of a triangle. Based on the delayed response model and anequation developed for calculating the volume of triangular deposition body, a methodfor simulating the erosion and deposition processes of the river reaches was proposed.The adjustment processes of the river reaches during1960and2011were simulatedusing the proposed method. The results showed that the method takes into account theeffects of both Tongguan elevation and water and sediment conditions. Moreover, it’sshown that Tongguan elevation significantly affected the evolution of the channelreaches, while income water and sediment conditions had greater influence on therecent aggradation and degradation processes of rivers.The lower Yellow Rive(rLYR)is affected by the water and sediment conditions aswell as the extension of the river mouth. Assuming the potential equilibrium channelreach has a trapezoidal deposition body, a calculation method for the volume of thetrapezoidal deposition body combined with the delayed response model were used to develop the calculation method for the non-equilibrium fluvial processes of the LYR.The evolution processs of the LYR during1952and2010were simulated using theproposed method and satisfactory results were obtained. The results showed that theproposed method considers the effects of water and sediment variation and estuaryextension on channel evolution. Meanwhile, it’s indicated that the aggradation anddegradation processes of the channel reach between Huayuankou and Lijin were closelyrelated to the income water and sediment conditions while the reach downstreamSunkou gaging station was more significantly affected by the rise of base-level causedby estuary extension.The vertical, lateral and longitudinal variations of channel geometry of the NorthFork Toutle River （NFTR） following volcanic eruption were analyzed. The resultsshowed that NFTR adjusted most rapidly during the first3years after the eruption. Therate of adjustment decayed as time elapsed and the channel gradually tended to a stableor equilibrium state. Moreover, the channel bed of the upper NFTR was severelydegraded while that of the lower reach aggraded. The aggradation and degradationprocesses of the channel bed during1980and2011were simulated by the delayedresponse model. The results showed that different modes of the delayed response modelcan well simulate the relaxation paths of the channel bed of the NFTR. Since thedelayed response model considers the cumulative effects of the water and sedimentconditions on the evolution of the river, it is able to simulate the adjustment processesof the river from a perturbed state after the eruption to a certain steady-state.