Based on the sediment-carrying capacity(SCC) and the feedback mechanism between SCC and erosion-sedimentation,a dynamical model for sediment transport in river network in lower-water season was proposed.The simulated results by this model reveal that as stream flow varies the quantity of erosion-sedimentation(QES) and the sediment-carrying coefficient(representing the SCC of the stream) change respectively in nearly opposite ways.This indicates the self-organized dynamics characteristics: according to the QES,the self-adjustment of the SCC tends to prevent a mass of erosion or the occurence of sedimentation.The transience of the dynamical process can fall in two successive phases.The first one is a faster phase and indicates the immediate response of the SCC to the changes of runoff.The second one is a slower phase and shows the dynamic effect is leading to the steady state.The responses of QES to the increase and decrease of the branch runoff are in nearly opposite ways:the increase of the stream flow can induce the fall of QES,while the decrease of the stream flow can result in the rise of QES.Therefore,the fluctuation of the stream flow,caused by the stochastic rainfall,may play an important role in keeping the QES relatively steady.