三角洲岸线变迁中的河流纵剖面实验

现代三角洲岸线变辽对河口变化频繁的河流有着不可忽视的影响.通过各种进口水沙过程和尾水位过程组合的水槽实验,建立了冲积河流纵剖面的发育模式.

AN EXPERIMENT FOR THE CHANGING OF STREAM PROEILFS DURING SHORELINE EVOLUTION IN A DELTA

The evolution of the shoreline in a delta area has an unnegliegidle effect on the longitudinal profile of a river with a frequently changeable estuary. This paper shows the results of six experiment sets with different conditions of water-sediment inflow and tail-water-level hydrograph.A deve opment mode of the profile of an alluvial river is found as follows;1.In the case that the sea current can carry away the material coming from the river, the shoreline would be stable, a linear profile in a sediment transport ebuilidrium state being formed, and the water level along the river would be stable.2.If the sea current can not carry the material, the shoreline would move seaward, a concave profile in a hynamic equilibrium state being formed, and the water level along the river would rise as the shoreline moves seaward.3.The periodical extension and migration of the estuary would cause a periodical fluctuation of water lever in the reach near the mouth, resulting in a time-dependent zigzag elevation of water level in the lower reach of an alluvial river. The amplitude would shrink upstream, eventually to zero at some point, where-upstream the water level would appear to rise continually. 4.The periodical change in conditions of water-sedment inflow would lead to changes of erosion and deposition on the river bed. If the sea current cannot carry the material coming from the river the location of the delta wou'd move seaward interruptedly as the inflow changes. In different periods, the water level in the river under the same condition of discharge would rise as well.However, in the case that the sea current can carry the material away, a linear profile in transport equiliblium would eventually de formed.5.The periodical change in condition of water-sediment inflow and the periodical fluctuation of water level in the reach near the mouth have different effects on the upper reach and lower reach of an alluvial riverain the upper reach, erosion or deposition would occur under different discharge, but the latter is dominant. Moreover, the water level under the same discharge would rise period by period, with a downstream-reducing effect. In the lower reach, affected by the estuary, the water level under the same dis charge appears to rise zigzagly with the same periods as the fluctuation of water level in the reach near the mouth, the amplitude shrinking upstream, eventually to zero.If the series of water-sediment flow as well as water level near the mouth are steady time series, there woulb be a trend of development from dynamic e equilibrium to transport equilibrium.6.Construction of reservoirs in the upper reach would result in a change in the condition of water and sediment in the lower reach. However, as the material will be scoured up in the reach right downstream of the reservoir, the sediment load to the sea will recover to the same value as before, so that the evolution tendency of the estuary would not be change.