三峡水库干流消落带泥沙沉积影响因素

Factors influencing sedimentation in the riparian zone of the Three Gorges Reservoir,China

为揭示三峡水库消落带不同自然环境因素对泥沙沉积过程的影响及判别人类活动的干扰程度,采用原位观测方法,对三峡水库干流消落带的泥沙沉积量及其潜在影响因素(消落带微地形、河流水文泥沙条件、消落带土壤侵蚀、消落带植被状况和人类活动)展开调查、分析和量化测算,并利用典型相关分析和方差分析,研究不同因素对泥沙沉积量的影响。结果表明:1)库尾江津—涪陵河段以人类活动的影响最为剧烈,自然环境因素与泥沙沉积量均无显著关系。2)库中涪陵—奉节河段以消落带地形特征中的坡度和高程影响较为明显,二者与泥沙沉积量的相关程度分别为-0.508和-0.714;坡度越小,泥沙沉积越多;高程越低,消落带被含沙水流淹没的时间越长,泥沙沉积量也越多。3)库首奉节-秭归段则以坡度的影响为主,其与泥沙沉积量的相关程度为-0.517,坡度越小,泥沙沉积越多,不同高程间的泥沙沉积量并无太大差异。研究说明,三峡水库干流消落带泥沙沉积影响因素主要包括消落带坡度、高程、河流水沙条件和人类活动4种,植被盖度对消落带泥沙沉积过程没有影响,4种因素的影响范围存在较明显的空间变异性。

[Background] Various factors may affect the sedimentation and erosion process in riparian zone, including terrain, sediment transport, water level fluctuations and human activity. [ Methods ] In order to reveal the influence of these environmental factors and the disturbance of human activity on the sediment deposition process in the riparian zone of the Three Gorges Reservoir, using in-situ observations, canonical correlation analysis, partial correlation analysis and variance analysis, this study investigated the amount of deposited sediment under different environmental conditions and the potential factors affecting sediment deposition in the riparian zone of the Three Gorges Reservoir and the relationship between them, including microtopography, hydro-sediment conditions of the river, soil erosion, vegetation condition and human activity. [ Results] Results showed that human activity was the main controlling factor in the upper reach from Jiangjin to Fuling, including gravel dredging, bank revetment and ports and wharfs constructing which disturbed considerable amounts of deposited sediment due to regular sediment cleaning, as a result, there was no natural law to dictate the distribution. Slope gradient and elevation being part of terrain features were the main controlling factors in the middle reach from Fuling to Fengjie with correlation coefficient of -0. 508 and -0. 714 respectively, and the amount of sediment deposition was greater in areas with a gentler slope or lower elevation. However, the influence of elevation on sedimentation played its role with the conducting of inundating duration which was a result of hydrologic regime controlled by the operating strategy of the Three Gorges Reservoir, since sites with lower elevations would be drowned by sediment-laden flow with a longer duration, leading to a larger amount of sediment deposition. Slope gradient also was a primary factor, particularly affecting the sedimentation in the lower reach from Fengjie to Zigui with correlation coefficient of -0. 517. The amount of deposited sediment was greater in the areas with a gentler slope but there was no difference between sampling points with different elevations but similar slopes. Because the slopes in this area were much steeper than other sections and the kinetic energy and velocity of the overland flow were much higher, making it difficult to deposit. [ Conclusions] This study found that slope gradient, elevation, hydro-sediment conditions of the river and human activity were the main factors that influenced sedimentation in the riparian zone of the Three Gorges Reservoir, while vegetation condition had no effect on sedimentation. Moreover, the four factors influenced a section of the river channel respectively instead of the entire channel in the reservoir, which represented obvious spatial variability.