澜沧江源河床沉积物分布特征——以扎曲囊谦河段为例

Sediment distribution on Nangqian Reach in the source area of Lancang River

基于对澜沧江源各冲积河段的考察分析,选定扎曲囊谦河段开展沿横断面钻孔采集河床沉积物,分析各沉积层沉积物的几何特性和沉积学特征,探讨沉积物粒度的空间变化规律。结果表明:囊谦河段沉积物以砂砾石为主,由跃移质和悬移质成分组成,无滚动沉积,其分选较差,自然分布频率曲线有2~4个峰度,主峰峰态高而窄,为典型的河床沉积曲线;沉积物粒径由上游至下游沿程减小,反映了峡谷壅水河段的泥沙沿程淤积分选规律;同一断面河槽附近沉积物粒径较粗,与水流动力分布一致,同时其沉积厚度亦较浅;洲滩沉积物粒径的垂向上分布呈现粗细交替、粗厚细薄的基本规律,可反映不同历史时期河道水文节律以及青藏高原气候的定性变化。

Based on the investigation and analysis of the alluvial reach in source area of the Lancang River, the Nangqian reach was selected to collect riverbed sediment by drilling along the cross section. The geometries and sedimentological characteristics in each sedimentary layer were analyzed to investigate the spatial variation of sediment size. Results indicate that local sediment is dominated by gravel, which consist of leaping and suspended components. There are 2 to 4 kurtosis peaks in the sediment particle size distribution frequency curve. The main peak is high and narrow. The sediment particle size decreases from upstream to downstream, reflecting the deposition separation law of sediment along the backwater reach of the canyon. In the same section, sediment near the river channel are coarser, consistent with the distribution of flow dynamic, and their deposition thickness is also relatively shallow. Sediment deposition on sandy beach appears alternately of coarse particles and fine particles in the vertical direction, while coarse particle is thicker and the fine sand is thinner. This basic rule reflects the hydrological rhythms of rivers in different historical periods and the qualitative changes in the climate of the Qinghai-Tibet Plateau.