自然河流或者处于单向演变状态,或者处于准平衡状态。这是按平均概念而言。实际河床演变就是围绕这种均衡状态或正或负地交替进行。河流一旦受到外力干扰,均衡状态被破坏之后,河床演变过程也将随之改变。有的干扰、改变甚至破坏会很强烈。这种演变开始时都比较急剧,然后逐渐衰减,最终达到新的均衡状态。干扰河床演变均衡状态的途径有二:(1)改变河道的来水来沙条件。如河段以上的水土保持工程、拦沙工程、水库枢纽工程、分流堵汊工程和引水工程等的作用。它们增减水量、沙量,改变水流过程和输沙过程以及水沙搭配关系等。(2)改变河段河床形 Natural rivers are either in a one-way evolution or in quasi-equilibrium. This is based on the average concept. The actual river bed evolution is around this equilibrium or positive or negative alternately. Once the river is disturbed by external forces and the equilibrium state is destroyed, the evolution of the river bed will also change. Some interference, change or even damage will be very strong. This evolution began sharply, and then gradually decayed to eventually reach a new equilibrium. There are two ways to interfere with the evolution of the river bed equilibrium: (1) Change the incoming water and sediment conditions of the river course. Such as the river above the soil and water conservation projects, silt blocking works, reservoir hub projects, diversion and closure projects and diversion works. They increase or decrease the amount of water, sediment, change the water flow and sediment transport process and the relationship between water and sediment. (2) to change the shape of the river bed