IMHE OpenIR  > 山地表生过程与生态调控重点实验室
三峡水库干流典型消落带沉积泥沙物源示踪
唐强
Thesis Advisor贺秀斌
2014
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Name博士
Degree Discipline土壤学
Keyword泥沙来源 示踪 消落带 三峡水库
Abstract三峡水库蓄水运行在坝址宜昌至库尾重庆间形成长660km,垂直落差30m,总面积达349km2的水库消落带。消落带泥沙沉积是特定的水库水位调节模式和长江上游泥沙输移特征共同作用的过程。判别各侵蚀产沙单元对三峡水库消落带沉积泥沙的贡献,对科学合理地制定长江上游水土保持措施和泥沙调控策略具有重要的现实意义和科学价值。论文通过现场调查和泥沙理化性质示踪,阐明三峡水库干流消落带泥沙沉积过程和物源分异,建立水库消落带泥沙沉积的季节性旋回识别方法,提出泥沙来源复合“指纹”示踪的诊断识别因子,具有创新性。论文主要结论如下: (1)通过现场调查和泥沙理化性质示踪,揭示三峡水库干流典型消落带断面泥沙沉积随高程分布的一般特征,初步阐明泥沙沉积过程和物源构成差异。泥沙多年累积净沉积速率随高程增加明显递减,与水库水位调节模式和长江上游泥沙输移的季节性特征密切相关。雨季水库低水位运行,侵蚀性降雨量增加导致上游主要入库支流及库区小流域输沙量显著增加,干流悬浮泥沙浓度增加,导致消落带下部(155m以下)泥沙大量沉积,年均沉积厚度达14.9cm,泥沙颗粒较细(粘粒比重大,中值粒径较小),137Cs比活度和有机质较低,表明主要来源于上游支流和库区小流域输沙;旱季水库高水位运行,上游支流及库区小流域输沙减少,消落带上部(155m以上)泥沙沉积厚度降低,年均沉积厚度为2.6cm,泥沙颗粒较粗(砂粒比重高,中值粒径较大),137Cs比活度较高,有机质含量较高,表明来源主要为消落带侵蚀泥沙。 (2)通过对三峡水库中游忠县坪山干流消落带沉积泥芯137Cs、粒度和有机质深度分布分析,建立了水库消落带沉积泥沙的季节性旋回识别方法:雨季沉积物主要来源于上游主要支流和库区小流域产沙,137Cs比活度和有机质较高,粒度较细;旱季沉积物主要来源于河流侵蚀(包括消落带侵蚀),137Cs比活度和有机质较低,粒度较粗。利用旱/雨季泥沙137Cs、粒度和有机质在沉积剖面的深度变化,识别出各年旱/雨季泥沙沉积厚度,结合采样时泥柱压缩系数,估算了2006~2013年逐年泥沙沉积厚度为29cm、36.2cm、65.2cm、94.2cm、152.2cm、43.4cm、65.2cm、14.5cm。 (3)通过对入库支流和沿库河段进行了悬浮泥沙和消落带沉积泥沙的粒径、137Cs、有机质和总氮的分析,揭示出泥沙在三峡水库运动输移过程及物源差异。悬浮泥沙和消落带沉积泥沙粒径沿水库纵向自上而下逐渐变细,表明泥沙输移运动过程发生颗粒筛选,粗颗粒优先在库尾河段发生了沉积;137Cs比活度、有机质和总氮自上而下逐渐增大,表明雨季三峡库区表层侵蚀泥沙在消落带沉积泥沙中所占的比重逐渐增加。 (4)运用泥沙来源复合“指纹”示踪技术,将消落带沉积泥沙来源划分为上游主要入库支流长江干流、嘉陵江和乌江输沙、三峡库区坡面侵蚀和小流域来沙和消落带侵蚀产沙,筛选出TN、137Cs、Mg、Ca和Mn具有诊断能力的指纹因子组合,定量估算了各物源对水库干流消落带泥沙的相对贡献率。
Other AbstractRegular impoundment of the Three Gorges Reservoir has created a riparian zone with a vertical height of 30 m and a total area of 349 km2 extending 660 km from Yichang to Chongqing. Significant sedimentation has occurred in the riparian zone which was determined by the specific type of reservoir regulation and seasonal variation of sediment yields from the Upper Yangtze River Basin. Discriminating the contribution of potential sources to sediment deposited in the riparian zone affords an important practical and scientific basis for implementing soil conservation practices and sediment abating strategies in the Upper Yangtze River Basin. This study preliminarily revealed the sedimentation processes and source composition of sediment in the riparian zone along the Yangtze mainstream of the Three Gorges Reservoir, presented a novel method to reconstruct the historical sedimentation processes in the riparian zone, and suggested a composite of fingerprints for sediment source tracing. The following principal conclusions were obtained: (1) The lateral change of sediment depth with elevation was revealed and the difference in sedimentation processes and source composition was highlighted by on-site surveying and tracing with geochemical fingerprints. Multi-year cumulative net sediment depth decreased abruptly with increasing elevation, which was closely related to the specific pattern of water level regulation induced by regular dam operation and the sediment dynamics in the Upper Yangtze River. During the wet season when the reservoir was operated at relatively lower water levels, increase in erosive rainfall may cause increase in sediment yields from upstream basins and local catchments led to high riverine suspended sediment concentrations, which consequently can cause significant amount of sediment deposited in the lower portions of the riparian zone (below 155m). The observed annual averaged sediment depth in this area of riparian zone was 14.9cm. Riparian sediment was characterized by higher clay fractions and smaller median particle size, and low 137Cs activity and organic matter content, indicating that the sediment mainly originated from upstream basins and local catchments. During the dry season when the reservoir was operated at relative higher water levels, sediment depth rapidly decreased due to decline in sediment yields from upstream basins and local catchments, with an annual average value of 2.6cm. The sediment was characterized by higher sandy fractions and larger median particle size, higher 137Cs activity and organic matter content, indicating the principal sediment source was sediment production from local bank erosion. (2) The sedimentation processes in a typical sedimentary riparian zone was reconstructed by analyzing the depth distribution of particle size, 137Cs activity and organic matter. Suspended sediment load during the wet season mainly originated from upstream tributary basins and local catchments, and was dominated by finer fractions and enriched with 137Cs and organic matter, while suspended sediment load during the dry season mainly originated from bank erosion, and was dominated by coarser fractions and depleted with 137Cs and organic matter content. Comparing the seasonal variation in sediment geochemical properties (particle size composition, 137Cs activity and organic matter) with the depth distribution of these attributes of the core sediment and applying the condense factor of sediment core during sampling, the annual sediment depth during 2006~2013 were estimated as 29cm、36.2cm、65.2cm、94.2cm、152.2cm、43.4cm、65.2cm、14.5cm, respectively。 (3) The difference in particle size and source composition during sediment delivery along the reservoir was assessed by analyzing the particle size distribution and 137Cs, organic matter and total nitrogen contents of both suspended sediments and riparian sediments. Particle selectivity has taken place during sediment delivery along the reservoir that coarse frac
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/7834
Collection山地表生过程与生态调控重点实验室
Recommended Citation
GB/T 7714
唐强. 三峡水库干流典型消落带沉积泥沙物源示踪[D]. 北京. 中国科学院研究生院,2014.
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