长江口典型河段表层悬沙浓度影响因子定量分析

发布时间：2018-04-01 18:22

本文选题：表层悬沙浓度　切入点：多元回归模型　出处：《华东师范大学》2017年硕士论文

【摘要】：河口悬沙是河口形成和发育的物质基础,其动力沉积过程与地貌演变密切相关,对于河槽的自然演变、人工建筑物的安全防护及周边生态环境的治理有着重要影响。受潮汐、径流、风浪及盐淡水混合作用影响,河口悬沙浓度变化复杂,随机特征显著,至今尚未有较好的表示方法,且由于观测条件等的影响,长时间连续的观测数据较难获得。本文以表层悬沙浓度为着眼点,基于随机理论,以长江河口上、中、下段固定站位多要素连续观测和定点水文资料为依据,分析潮汐、径流、盐度、风浪等影响因子对河口悬沙的作用,建立长江河口表层悬沙多元回归模型计算式,量化各因子在河口不同区域对悬沙浓度的贡献,为数值模拟、航道回淤计算问题等提供重要的参数。长江口复杂的动力要素和地形特点以及区域气候的影响,使得风速、径流量、潮差、盐度、悬沙浓度、流速等都呈现了复杂的时空变化特征。受冬夏季风气候影响,长江口风向以偏北风和东南风向为主;月均径流量变化显著,表现为洪季流量高、枯季流量小的特点,潮差变化趋势则与径流量相反;悬沙浓度、盐度和流速的洪枯季、大小潮及涨落潮均值在长江口不同区域会有所差异,三者的垂向变化上,悬沙浓度和盐度一般从表层至底层逐渐增大,流速则相反。根据小波分析和长周期及极端条件作用下的悬沙变化特点,我们发现悬沙浓度的季节性变化、大小潮变化等周期性的变化特征与周期性动力因素有关(如径-潮流的强度的交替),而大风、人为活动等随机性动力因素作用则会导致悬沙浓度的快速增长。统计表明,径流量、盐度、潮差、风速与悬沙浓度变化关系密切,但长江河口上、中、下段不同测站模型的主要影响因子有所差异。徐六泾站悬沙浓度预测模型主要由径流量、潮差和风速控制;佘山站由盐度、潮差和风速控制;横沙站则综合了以上两个站点的控制因素,由径流量、盐度、潮差和风速共同影响。通过多元回归方程完成对表层悬沙浓度预测模型的建立,经实测资料验证,模型具有很好的精确度(83.3%)。长江口上、中、下段站点各因子对表层悬沙浓度的贡献不同:徐六泾站径流量、潮差、风速所占权重分别为45.6%、40.0%和14.4%,径流对于悬沙浓度变化影响最大,其次为潮差与风速;横沙站径流量、潮差、盐度、风速所占权重分别为17.9%、47.2%、13.5%和21.4%,潮差是最为主要的影响因子,其次为风速和径流量,盐度相对较小;而佘山站潮差、盐度、风速所占权重分别为43.4%、26.5%、和30.1%,最主要的影响因子也是潮差,其次为风速和盐度。对比同一影响因子在长江河口上、中、下段对表层悬沙浓度平均值和最大值的贡献,可以反映其在不同地貌环境条件下对悬沙浓度的影响强弱。对于平均悬沙浓度贡献来说:佘山站潮差引起的表层悬沙增量最大;径流量对徐六泾和横沙站悬沙浓度贡献值相近,至口外佘山站,径流所携带的泥沙对表层悬沙浓度贡献已明显衰弱;潮差、盐度和风速引起的悬沙浓度增量从徐六泾至口外佘山站依次递增。结合各因素引起的最大悬沙浓度变化来看,在一般天气情况下,风浪作用对表层悬沙的影响弱于潮汐,但在风浪较大的天气状态下,风速引起的表层悬沙浓度变化可达1kg/m3以上,成为悬浮泥沙含量变化的主控因子。模型的计算结果表明:近10多年来在长江来水来沙减少背景下,由径流携带的水体表层悬沙浓度有减小趋势,致使河口上段地区表层悬沙浓度减小;但在河口中下段及口外地区,由于径流作用减弱,表层悬沙浓度在潮汐、风浪、盐度等因子的共同作用下,未出现显著变化。
[Abstract]:Suspended sediment is the mouth of the formation and development of the material basis, the sedimentary processes and geomorphic evolution is closely related to natural channel evolution, has an important impact on governance safety protection of artificial structure and the surrounding ecological environment. By tide, runoff, wind and salt water mixing effect of estuary suspended sediment concentration change is complex. The stochastic characteristics significantly, there has not been any good representations, and because of the influence of the observation conditions, long time continuous observation data are hard to obtain. In this paper, the surface suspended sediment concentration as the starting point, based on the random theory, the Yangtze River Estuary, and fixed elements under continuous observation stations and hydrological data point analysis of runoff, tide, salinity, wind and other factors of suspended sediment on the estuary of Yangtze River Estuary, surface sediment calculation formula of multiple regression model to quantify the factors in different regions of the estuary The concentration of suspended sediment contribution for the numerical simulation, the channel siltation calculation provides important parameters. The mouth of the Yangtze River complex dynamic factors and terrain features and regional climate effect, the wind velocity, runoff, tide, salinity, suspended sediment concentration and velocity are presented. By complex spatial and temporal variation characteristics of winter and summer the wind climate, wind direction to the mouth of the Yangtze River and north wind southeast wind; average monthly runoff change significantly, as the flood season flow, flow characteristics of the dry season, tidal and runoff change trend is the opposite; suspended sediment concentration, salinity and velocity of the flood and dry season, and in the mean tidal tide the mouth of the Yangtze River in different regions will be different, the three vertical variation, suspended sediment concentration and salinity generally increases gradually from the surface to the bottom, the velocity of suspended sediment on the contrary. According to the characteristics of wavelet analysis and long cycle and extreme conditions, we found that The seasonal variation of suspended sediment concentration changes, changes in the size of the tide and other cyclical characteristics related to cyclical factors (such as dynamic alternate diameter trend strength), and wind, human activities such as the stochastic dynamic factors will lead to the rapid growth of the suspended sediment concentration. Statistics show that the runoff, salinity, tidal range the wind speed, and the suspended sediment concentrations in the close relationship, but the Yangtze River Estuary, and under different test station main influence factor of a model of difference. Xu six suspended sediment concentration forecasting model Jinghe station mainly consists of runoff, tidal and wind control; Sheshan station by salinity, tidal and wind control; Hengsha station comprehensive the control factors of more than two sites, by runoff, salinity, tidal and wind speed influence. Through multiple regression equation, the prediction model of surface suspended sediment concentration, verified by measured data, the model has good accuracy (83.3%) of Yangtze River. In the mouth, each factor under the site of suspended sediment concentration on surface runoff, the contribution of different: Xu Jing six tide station, wind speed weights were 45.6%, 40% and 14.4%, the biggest impact on the runoff variations of suspended sediment concentration, followed by tidal and wind; runoff, tide difference Hengsha station, salinity the wind speed, the weights were 17.9%, 47.2%, 13.5% and 21.4%, the tidal range is the most dominant factor, followed by wind and runoff, salinity is relatively small; and Sheshan station tidal salinity, wind speed, the weights were 43.4%, 26.5%, and 30.1%, is the main factor affecting the tidal range. The wind velocity and salinity. Compared to the same factors in the Yangtze River Estuary, in the lower section of the surface, the concentration of suspended sediment in the mean and maximum contribution, can reflect the environmental conditions in different topographic effects on suspended sediment concentration. The average intensity for suspended sediment concentration contribution: Sheshan tide station The difference caused by the increment of surface suspended sediment runoff of six; Xu Jing and Hengsha station suspended sediment concentration contribution value similar to the Sheshan station, sediment carried by the surface suspended sediment concentration contribution has been significantly weakened; tide, salinity and wind speed caused by the suspended sediment concentration increment from Xu Liujing to Sheshan station in increasing estuary caused by various factors. Combining with the maximum sediment concentration changes, in general weather conditions, effects of wind waves on the surface of the suspended sediment in the weak tide, but in large waves weather conditions, wind speed caused by surface suspended sediment concentration changes of up to 1kg/ above m3, become the main control factors of changes of suspended sediment concentration model. The calculation results show that nearly 10 years of sediment in the Yangtze River water to reduce the background by runoff water surface suspended sediment concentration decreases, the surface area of upper estuary suspended sediment concentration decreases; but in estuaries There is no significant change in the surface suspended sediment concentration under the interaction of tides, wind waves and salinity due to the weakening of the Runoff Effect in the lower and outside regions.

【学位授予单位】：华东师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV148

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