长江入海水沙通量变化过程分析及变化趋势

An Analysis of the Processes and Trends of Changes in Yangtze River Water and Sediment Fluxes into the Ocean

针对河流入海水沙通量变化问题,以长江为研究对象,基于1950~2017年大通站及各组分实测水沙和降雨量数据,在分析入海水沙和各组分变化过程及各组分贡献比例的基础上,确定主要贡献组分,进而预测入海水沙通量的变化趋势。结果表明:(1)各组分年径流量和降雨量的多年变化均不大,使得大通站入海年径流量多年变化不大,宜昌站对入海年径流量的贡献比例为48%。(2)大通站入海流量年内分配过程逐渐坦化,其中宜昌站为主要贡献组分,洪枯季平均贡献比例分别为233.79%和80.36%;宜昌站的主要贡献作用体现了其上游梯级水库群对大通站入海流量过程的调平效应。(3)流域水库建设将使得大通站入海流量过程坦化和年径流量稳定的趋势得以维持。(4)大通站年入海沙量自1985年起显著减少,三峡水库蓄水前大通站泥沙主要来自宜昌,其贡献比例为116.04%,三峡水库蓄水后,大通站泥沙主要来自宜昌-大通区间的河床补给,其贡献比例为53.29%;水库下游河床补给逐渐减少和水库淤积平衡时间延长将使得大通站多年平均入海沙量在较长时期内(>300年)不超过1.5×10^8 t/a。

To address the problem of changes in river water and sediment fluxes into the ocean,the Yangtze River was used as a subject of this study based on the field measurements of water,sediment and rainfall data at Datong station and its components from 1950 to 2017.By analyzing the processes of changes of the water and sediment entering the ocean and the various components and their contributing ratios,the principal contributing components were determined,and the trends of changes in water and sediment fluxes into the ocean were predicted.The results show that:(1)The annual runoff of each component and the rainfall had not changed much for many years,and as a consequence,the change in annual runoff from Datong station into the ocean had been unobvious.The contribution of Yichang station to the annual runoff to the ocean was 48%.(2)The intra-annual process of water flux from Datong station into the ocean gradually became more evenly distributed,with Yichang station as the primary contributing component,and the average contributing ratios during the flooding and low water seasons were 233.79%and 80.36%,respectively.The primary contribution of Yichang station reflects the smoothing effect of the upstream cascade reservoir group on the process of water flux from Datong station to the ocean.(3)Basin reservoir construction tends to maintain the flattening effect on the intra-annual process of water flux from Datong station into the ocean and the stabilization of the annual runoff.(4)The annual sediment load at Datong station had decreased significantly since 1985.The sediment at Datong station was primarily from Yichang station before the impoundment of the Three Gorges Reservoir,and the contributing ratio was 116.04%.After the impoundment of the Three Gorges Reservoir,the sediment at Datong station was mainly replenished from the riverbed along the reach between Yichang and Datong,and the contributing ratio was 53.29%.The gradual reduction in riverbed replenishment downstream of the reservoir and the prolonged reservoir sedimentation time are expected to prevent the average sediment load entering the ocean from exceeding 1.5×10^8 t/a for a long period of time(>300 years).