Abstract:

Strong human activities have changed the fluvial flux of lowland alluvial rivers (LARs) and are rapidly changing the integrities of the geomorphology, habitation and the ecosystems of LARs as a whole. To preserve the health (stability and long-term safety) of LARs is one of the greatest challenges we are facing. In this paper, we analyzed the relationship of the longitudinal slope of LARs with flow and sediment conditions. We revealed a dominant effect of coarse sediment (CS), small proportion in the sediment load from upstream, on the equilibrium slope (ES) and stability of LARs. In the meantime, such CS has been proved selectively deposited in the upstream reservoirs and it is possible with present technically and economically accepted effort to remove it downstream. As a result, we suggested to investigate 1) the feasibility of dredging 20-30Mt/yr CS from the fluctuating backwater reach of the Three Gorges Reservoir, delivering it downstream to prevent the dramatically incising middle Yangtze River; and 2) the possibility of using the Xiaolangdi reservoir in the same way but to remove 50 Mt/yr CS out of the ever-rising Lower Yellow River so to help this vulnerable river achieving a long-term stability.

Key words: coarse sediment, alluvial river, equilibrium slope, restoration