三峡工程蓄水运用对长江口径流来沙的影响

EFFECT OF THE THREE GORGES PROJECT ON SEDIMENT TRANSPORTATION OF THE YANGTZE ESTUARY

三峡工程蓄水运用后,下游来沙量大大减少,直接影响长江口的径流来沙量。依据实测资料,统计计算了宜昌、大通及中间水文站各粒径组泥沙多年平均输沙量。考虑到沿程冲淤变化及区间支流来沙,建立了上下游水文站各粒径组泥沙输沙量之间的对应关系,初步探讨了宜昌和大通两站不同粒径组泥沙输沙量之间的关系。在此基础上,根据一维数学模型的计算结果,分析了三峡工程蓄水后宜昌站各粒径组泥沙的来沙量的减少及大通站各粒径组泥沙输沙量相应的变化。结果表明:在输沙总量上,大通站输沙量中的70%来自宜昌上游河道,其余的则来自区间的补充;如果考虑不同粒径组,则细颗粒对上游来沙的依赖程度高于中等粒径泥沙,三峡建库后,在不考虑沿程冲刷恢复的条件下,宜昌上游来沙量减少了71.7%,通过大通站的输沙量较建库前减少了40%;其中细颗粒减少的程度低于中等粒径颗粒。

After the completion of the Three Gorges Project, the sediment runoff of the lower reaches will decrease to a significant extent. On the basis of statistical calculations of fields data, the dependence between Yichang's and Datong's annually average sediment discharge and that of different grain size fraction have been analyzed by considering the local income. It has been concluded that about 70% of the sediment discharge through Datong depends on that amount through Yichang, in which 96% of the discharge of fine particle (d<0.025 mm) through Datong comes from Yichang, and 53.8%, 73.8% for mean particles (0.025 mm<d<0.1 mm) and coarse particles (d>0.1 mm) respectively. The construction of Three Gorges Project makes the sediment discharge through Yichang decrease to the extent of 71.7%, because of the confluence of tributary, the sediment transported through Datong to the Yangtze Estuary decrease to an extent of 40%, for the different dependence, descendant of sediment discharge for different fraction varies with grain sizes, i.e. 29.6% of fine particles decrease and meanwhile, 47.9% and 37% for mean and coarse particles respectively.