Response of bedload transport, submarine topography, and dune internal structures to typhoon processes off Dongfang coast in the Beibu Gulf

Bedload sediment transport was estimated by the SEDTRANS96 model based on three-day hydrodynamics data obtained off the Dongfang coast in the Beibu Gulf during Typhoon Ketsana in September 2009. Bed- forms on the sea floor off the Dongfang coast and internal structures of a typical dune were interpreted to evaluate storm influences on individual dunes and the dune field. Results indicated that flow forcings and related bedload transport were both strengthened significantly due to Typhoon Ketsana. The measurements and modeling results, which mainly included three different stages, presented noticeable phasic variation. The three stages were dominated by tidal current （Period I）, tidal current combined with wind-induced waves （Period II）, and swells combined with tidal current and seaward flows （Period III）. This phasic varia- tion could be a common trait of hydrodynamics due to typhoons moving westwardly to the south of Hainan Island and Beibu Gulf in South China Sea. Results indicated that the maximum bedioad transport rate for every burst in Period III was almost 100 times larger than that in Period I and was ten times larger than that in Period II. However, the short-term increase in bedload transport induced by storms like Ketsana did not change the long-term evolution of dune morphology. Evidence was given by the internal structures of a typical dune, which revealed renewed modification under subsequent moderate conditions after storm ero- sion. Instead, storms may influence at different scales and regional allocation of sand dunes in some large areas because changes of the sea floor in large scales can hardly be recovered. More surveys during and after storm passage are also needed to document the level of positive contribution to forward migration.

Effect of upward seepage on bedload transport rate

The paper presents an investigation of injection effects on the bedload transport rate. According to dimensional analysis, two dimensionless groups, an Einstein＇s parameter group and a modified densimetric Froude number group, were chosen to examine how injection affects the bedload transport rate. Experimental studies were conducted in an open-channel flume with an upward seepage zone. The sediment particles used for the test were 0.9 mm in diameter. The experimental results show that an increase in the injection velocity causes a reduction in the shear velocity excess, which is defined as the difference between the shear and critical shear velocities, leading to a reduction in the bedload transport rate. The equation for predicting the bedload transport rate in the presence of upward seepage was derived empirically. The proposed prediction method is suitable for engineering practice, since it only requires the undisturbed flow condition, properties of sediment particles, and the injection velocity.

Development and installation of bedload monitoring systems with submerged load cells

Bedload governs riverbed channel variations and morphology, it is necessary to determine bedload discharge through an arbitrary cross section in a mountain fiver. A new system with submerged load cells has been developed to directly measure bedload discharge. The system consists of： （1） an iron box which is 1 m long, 0.5 m wide and 0.1 m in depth, （2） two submerged load cells 0.7 m apart, （3） a pressure sensor and, （4） an electromagnetic velocity meter. This system has been designed to exclude the effect of the hydraulic pressure of water on direct measurements of bedload particle weight. Initial tests in a laboratory were conducted to examine the accuracy of measurements with the system under aerial conditions. The system has been installed in the supercritical flume in Ashi-arai-dani River of the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute （DPRI） of Kyoto University to obtain bedload discharge under natural conditions. Flume tests were conducted in this channel by artificial supply of uniform sediment particles of several grain sizes. The average velocity of the sediment particles near the bed was estimated using cross-correlation functions for weight waves obtained by the two load cells, Bedload discharge calculations were based on time integration of the product of sediment velocity and sediment weight obtained by the two load cells. This study clarifies the reasons why bedload measurements are difficult, and provides some solutions using the monitoring systems with submerged load cells through the field measurements. Additionally, the applicability of bedload measurement with the submerged load cells is explained based on experimental artificial sediment supply data.

Prediction of bedload transport inside vegetation canopies with natural morphology

Due to vegetation drag and vegetation-generated turbulence,bedload transport in vegetated channels is more complicated than that in nonvegetated channels.It is challenging to obtain accurate predictions of bedload transport in vegetated channels.Previous studies generally used rigid circular cylinders to simulate vegetation,and the impact of plant morphology on bedload transport was typically ignored;these methods deviate from natural scenarios,resulting in prediction errors in transport rates of more than an order of magnitude.This study measured bedload transport rates inside P.australis,A.calamus and T.latifolia canopies and in arrays of rigid cylinders for comparison.The impact of plant morphology on bedload transport in vegetated channels was examined.Inside the canopies of natural morphology,the primary factor driving bedload transport is the near-bed turbulent kinetic energy(TKE),which consists of both bed-generated and vegetation-generated turbulence.A method was proposed to predict the near-bed TKE inside canopies with natural morphology.For the same solid volume fraction of plants,the transport rate inside canopies with a natural morphology is greater than or equal to that within an array of rigid cylinders,depending on the plant shape.This finding indicates that plant morphology has a significant impact on transport rates in vegetated regions and cannot be ignored,which is typical in practice.Four classic bedload transport equations(the Meyer-Peter-Müller,Einstein,Engelund and Dou equations),which are suitable for bare channels(no vegetation),were modified in terms of the near-bed TKE.The predicted near-bed TKE was inserted into these four equations to predict the transport rate in canopies with natural morphology.A comparison of the predictions indicated that the Meyer-Peter-Müller equation had the highest accuracy in predicting the transport rate in vegetated landscapes.

基于振动信号的推移质输沙率监测研究

推移质输沙率精确测量是河流动力学的研究难点之一,传统的推移质直接测量方法受限于推移质运动的复杂性和测量仪器的局限性,无法对推移质进行长时间的连续监测。为了连续监测推移质运动,采用推移质间接测量方法,利用安装振动传感器的冲击板系统对推移质运动产生的振动信号进行高分辨率采集,提取振动信号特征值,并建立与推移质输沙率及流量之间的关系,进一步采用人工神经网络算法对推移质输沙率进行有效预测。结果表明:推移质振动信号的特征值均值与推移质输沙率有良好的相关性;中等流量条件的神经网络预测效果最佳,小流量条件的预测效果次之,大流量条件的预测效果相对较差,且其最优输入参数与流量及河床变化均有关系。

极端降雨事件下三峡库区中部多尺度嵌套小流域径流泥沙特征分析

为研究三峡库区中部泥沙来源及类型分布,本文基于中国科学院成都山地灾害与环境研究所万州典型区水土保持监测站多尺度嵌套小流域2003—2022年降雨极值与泥沙特征数据,利用Mann-Kendall秩相关检验,深入分析了库区流域内输沙量趋势变化及其与降雨极值之间的关系。结果表明:(1)三峡库区中部典型区小流域降雨天数和中雨、大雨以及暴雨天数有明显增加趋势;(2)支沟向出口汇聚过程中,部分推移质泥沙沉积,但在极端降雨时,沉积泥沙再次启动汇入下游,且极端降雨事件下流域坡面泥沙主要以悬移质形式流失;(3)由于人为活动的影响,嵌套小流域内各支沟和集水区的侵蚀模数存在显著差异,最大侵蚀模数与最小侵蚀模数之间的比值高达10.71。同时,小流域及其嵌套支沟的年侵蚀模数呈现不同程度增加的趋势,并在极端降水事件频繁发生的2020年达到最大值。(4)虽然三峡库区中部典型区小流域降雨整体上有降低趋势,但极端性的降雨频发仍是水土流失防治的重点区域。因此,针对频发的极端性降雨侵蚀特征及其小流域内泥沙迁移规律,加强小流域推移质与悬移质源头生态风险排除与治理,稳固河道沉积泥沙将有效降低小流域把口站泥沙的输出。

Single and joint effects of HHCB and cadmium on zebrafish （Danio rerio） in feculent water containing bedloads

As an important type of emerging pollutants, ecological toxicity and risk of artificial musks are increasingly concerned. Thus, single and joint toxic effects of 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8- hexamethylcyclopenta-gamma-2-benzopyran （HHCB） as one of the most widely applied artificial musks and cadmium （Cd） as an toxic metal on zebrafish （Danio rerio） were investigated by the exposure of zebrafish to various concentrations of HHCB or/and Cd in feculent water containing bedloads. The results indicated that the joint effect of HHCB and Cd changed during different exposure times within 120 h. The index of the antioxidant enzyme system including superoxide dismutase （SOD） and perox- idase （POD）, and malondialdehyde （MDA） were sensitive and induced in the zebrafish stressed by Cd, and content of soluble protein （SP） was sensitive to HHCB and could be used as a biomarker for HHCB. Joint effects on antioxidant enzymes depended more on the effect of single Cd in the first one or two days. However, in the rest exposure days, the effect of HHCB began to dominate in the joint effect during the exposure process.

Incipient motion of non-uniform coarse grain of bedload considering the impact of two-way exposure

The incipient motion of bedload is due to the interaction between the flow and sediment.It is stochastically correlated with the flow structure,the sediment gradation and the arrangement of grains on the bed surface.The random position of the sediment on bed can be represented by a hiding factor or an exposure degree.Based on the numerical simulation of the disturbed flow in the interstice of grains,the influence of the two-way exposure degree(the vertical exposure degree and the longitudinal exposure degree) on the coarse grain incipient motion was investigated in this work.Results show that the exposure degree varies with the position of the sediment on the bed,which influences the flow structure around the particle and the incipient motion.In this paper,the major research achievements on this phenomenon include:Firstly,a mathematical model is established for the rolling-pattern incipient motion of the coarse grain under a critical state of moment balance.The influence of the partial disturbed flow is considered.Secondly,the two-way relative-exposure-degree probability distribution functions are developed to reflect the influence of the disturbed flow and the random arrangement of sediments.Thirdly,a formula to calculate the incipient velocity is presented based on the above results,which considers the impact of the two-way exposure degree of sediment particles.

基于潮流模拟的琼州海峡东口动力地貌分析

潮流是塑造琼州海峡东口海底地貌的主要动力,研究潮流作用下的沉积物运动特征,有助于更好地理解海峡的水沙通量、沉积过程和地貌演化。根据对2008和2015年研究区249个站位所采集的表层样品调查数据的研究统计,海峡东口沉积物以砂砾质为主,其分布规律与潮流的强弱和方向关系密切,运动形式主要为推移方式。为了进一步研究沉积物的运移与海底地貌的动态关系,利用沉积动力学模型估算了琼州海峡东口的潮流过程、沉积物输运率和侵蚀淤积强度等指标。结果显示,大潮时,东向急流的流速为0.9~2.0 m/s,西向急流为0.8~1.7 m/s,中潮和小潮的潮流流速约为大潮时的50%~60%。总体上,东向流强于西向流,但在海峡北岸和中央水道,西向流始终强于东向流。大潮时,全区沉积物的活动频率普遍较高,均值可达60%,其平均输运率在10^(−2)kg/(m·s)量级;而中小潮期间,活动频率均值仅为18%左右,平均输运率比大潮期小1~2个数量级。沉积物整体输运方向为东向,但在海峡北岸净输运方向为西向。从侵蚀淤积强度的分布可知,研究区的浅滩堆积速率较高,水道的侵蚀速率较高,量级可达10^(−1) m/a。

Study of bedload transport in backwater flow

This paper studies the flow structure and the bedload transport regime in backwater flows, to provide a theoretical support for solving the sediment transport and bed scour problems in rivers or reservoirs with backwater. The bedload transport rates under different conditions are analyzed first on the basis of theoretical analysis, measurement comparison and flume experiment, and it is pointed out that the existing formulas for the bedload transport rate are not applicable for the bedload transport rate in backwater flows. Next, the flow structure in a non-uniform flow is observed by flume experiments, and by introducing the backwater degree index, the quantitative relation between the relative bed shear stress and the backwater degree is obtained. Finally, the formula for the bedload transport rate applicable for the reservoir channel segment with backwater flows is obtained through measurements and flume experiments.

Interpreting grain-size trends associated with bedload transport on the intertidal fiats at Dafeng，central Jiangsu coast

A MIDAS-400 customized data acquisi- tion system has been used for the high-resolution sediment dynamic measurements over the Dafeng intertidal flats of northern Jiangsu during 6 tidal cy- cles from July 3 to July 10, 2003. The bed shear stress and bedload transport rates, in response to wave-current interactions, are calculated, which in- dicate that wind waves enhance the bottom shear stress and bedload transport rates. At the station for measurements, bedload transport was directed to seaward, with a sediment discharge of 30—150 kg·m?1 per tidal cycle. The surficial sediment samples were collected from a grid with 10 m spatial intervals over a rectangle 2×104 m2 experimental area, near the MIDAS-400 during the spring tide of July 4, 2003, and the neap tide of July 9, 2003. In addition, leveling survey was undertaken to obtain the detailed topog- raphy of the sampling area. Grain-size trend analysis of the sediment samples shows that the bedload transport patterns are complex, mainly controlled by the hydrodynamics and local geomorphology (e.g. tidal creeks) over the intertidal flats. Furthermore, the grain-size trends pattern during the neap tide rather than during the spring tide is consistent with the cal- culated bedload transport, and the grain-size trend vectors for the spring tide are larger than those forthe neap tide, indicating that the sampling thickness of surficial sediment during the neap tide may contain the information on the geomorphological evolution (or sediment deposition/erosion) from the spring to the neap tide.

基于数值模拟的琼州海峡东口推移质输运量估算

琼州海峡东口沉积作用主要受东西向往复流的控制,并呈现涨潮东流、落潮东流、涨潮西流和落潮西流4种形式,独特的沉积动力特征使得海峡东口分布大量潮流沙脊。沉积动力研究对于该区域海砂的开发和海底稳定性评估具有重要意义。海峡东口沉积作用的数值模拟计算表明:在中央水道、海峡北岸和浅滩区,潮流流速相对较大,其垂向平均流速可达0.7~1.0 m/s,其他区域流速为0.3~0.5 m/s;东向流流速较西向流大,但在海峡北岸,粤西沿岸流的存在使得西向流显著大于东向流,该特征在大潮期间尤为明显,小潮期间的流速普遍小于大潮时段,一般大潮流速是小潮的1.5~2.0倍。底质类型显示,研究区以砂砾质沉积为主,主要分布在中央水道、浅滩区和海峡北岸海域,全区平均粒径均值Φ为2.67,总体分选较差。研究区临界起动流速范围为0.12~0.79 m/s,在中央水道至西南浅滩一带临界起动流速在0.6 m/s以上,砂质沉积区起动流速多为0.35~0.45 m/s,而东部陆架的泥质沉积区起动流速基本小于0.22 m/s。Bagnold输运率计算模型结果显示:海峡北岸的输运率最大,其次为中央水道和浅滩区;其分布大小与潮流沙脊的位置和走向具有较好的一致性,潮周期内的净输运趋势在海峡北岸为西向,其他区域多为东向;大小潮的净输运量相差一个数量级,剖面计算得出一个月内通过琼州海峡东口的推移质净通量可达108 kg量级且总体方向为东向。

平整输沙床面水流阻力研究

水流阻力对于研究水流结构、推移质运动和输沙率等问题具有重要意义。影响水流阻力的因素有床面泥沙级配、水流条件、床面结构和推移质输沙率等,综合考虑床面泥沙条件、水流条件和推移质输移情况,将平整非均匀床面的水流阻力划分为沙粒阻力和输沙阻力。基于床面粗化过程中推移质输沙率的变化规律,将床面表层粗化程度系数表示为相对输沙率的函数,结合粗化完成床面和均匀床面的阻力公式,建立了包含床面结构参数的床面沙粒阻力公式。基于滚动和跃移推移质运动特性的差异,分析了滚动推移质在床面上的受力,得到了水流搬运滚动推移质消耗的能量,并与bagnold建立的计算公式进行对比,结合不同水流强度下滚动和跃移推移质的占比,建立了输沙阻力公式,由实测粗化床面资料确定了床面表层粗化程度系数,最终建立了适用于平整非均匀输沙床面的水流阻力计算公式。经实测资料验证并与其他学者的阻力计算公式进行分析对比,公式的均方根相对误差(RMSRE)仅为0.094,比其他学者阻力计算公式的相对误差值更小,表明该阻力计算公式具有更高的计算精度。

沙波与刚性非淹没植物复合床面推移质泥沙输移特性研究

鉴于复合床面条件下刚性非淹没植物改变推移质输沙特性的相关研究成果较少,为此采用水槽试验和理论分析方法,研究了平行排列的刚性非淹没植物对泥沙起动谢尔兹数和推移质输沙强度的影响。结果表明,平行排列的刚性非淹没植物使得泥沙起动谢尔兹数增大了97.2%,推移质输沙率降低了80%以上。通过理论分析提出了适用于刚性非淹没植物平行排列条件下恩格隆推移质输沙率公式,经验证该公式具有较高的精确度。

长江河口九段沙沙洲形成和演变过程研究

九段沙继崇明岛、长兴岛和横沙岛后成为长江河口第三代新生冲积沙洲(岛),为河口第三级分汊口沙洲,如今0m以上沙洲面积为126km2,5m水深包络的面积为448.7km2,平面外形成长椭圆沙洲。自从上世纪50年代中期九段沙成为独立沙体以来,在河口水流的作用下,不断地承接上游河道推移而来的底沙,沙洲持续淤涨,0m以上沙洲面积是原始面积的3.3倍,2m水深包络的平面面积是原始面积的2.5倍,5m水深包络的平面面积是原始面积的2.0倍多。与此同时,在陆海相互作用及南北槽分水分沙比值不断更替变化过程中,九段沙沙体本身也发生了较大变化,表现为沙头冲刷后退,沙尾淤涨延伸,南侧淤涨幅度大于北侧,而沙洲基座长轴位置移动不大。目前九段沙头部鱼嘴和北部导堤工程的建设改变了九段沙浅滩的水沙运动过程,因九段沙北侧边界基本固定,导致南侧边滩冲淤变化必将会增大,需采取相应的人工干预措施,才能使国家级生态保护区九段沙朝着健康的演变方向发展,同时减少对与沙洲相邻的南北槽通海航道水深的影响,确保通海航道畅通无阻。

长江口南港航道沙波群研究

本文利用Ｉｎｎｅｒｓｐａｃｅ４４９热敏式双频测深仪和ＧＰＳ（全球定位系统）在长江口南港和南北槽主航道走航观测结果，确认南港（吴淞口以下）上段航道在洪季正常风况下存在尺度较大的沙波群，并对沙波的几何特征、形成条件、迁移速率以及台风后的变化做了初步分析。结果表明：（１）在统计的６５２个沙波中，平均和最大波长分别为２１ｍ和１０５ｍ。平均和最大波高分别为０．８ｍ和２．７ｍ，波高和波长间具有明显的正相关关系；沙波中７２％为单一沙波，复合沙波的波长和沙波指数较大；单一沙波最大、最小和平均沙波指数分别为３６．５、１１．２和２１．８（复合沙波最大可达６９．３）；随着沙波度的增大，沙波指数呈增大趋势；绝大多数沙波（波高＜１ｍ）是对称或近于对称的，但波高＞１ｍ的沙波通常向海倾斜。（２）沙波沉积物为分选好的细沙，Φ５０为２．７０。（３）沙波现场水流费劳德数Ｆｒ小于０．２，与某些理论相符而与某些水槽实验结果相冲突。（４）大潮和寻常潮一个涨（落）潮过程沙波来回迁移的距离约为１～５ｍ；小潮期间沙波的迁移距离接近０；落潮迁移距离总是大于涨潮。（５）台风后沙波有被掩埋的迹象。结果包括：①沙质床底是形成沙波的重要基础。南北槽虽具有沙波形成的?

长江河口底沙运动规律

于1981－1988年以浅地层剖面仪和回声测深仪取得沙波观测资料，运用这些资料以及河床表层沉积物和历年河口水文、地形资料，采用水文学、沉积学与泥沙运动力学相结合的研究方法，分析长江河口底沙的运移规律。结果表明：长江河口底沙运动非常频繁，一般有单颗粒滚动、跳跃，沙波及沙体推移等形式；在沙质床面上沙波发育良好，其形成、发展和消失与潮差和落潮流速有一定的相关性，因受涨、落潮流改造，沙波难于得到充分发展；沙体推移为长江河口底沙运动的主要形式，推移量很大，有时甚至能使滩槽移位，迫使通海航道改线。研究底沙运动规律为长江河口治理提供科学依据。

长江河口枯季河床沉积物与河床沙波现场观测研究

于 2 0 0 2年 3月利用浅地层剖面仪、双频道测深仪、旁侧声纳和ADCP流速剖面仪、ENDECO海流仪、OBS测沙仪在江阴至横沙岛航行 1 50km ,取得河床沉积物、河床形态和与此相关的动力因子实测资料。采用沉积学和泥沙运动力学相结合的方法进行研究 ,结果表明 :观测期间该河段河床沉积物颗粒组成以细砂为主 ,中值粒径为 2 φ左右 ,分选较好 ;河床泥沙以单颗粒群体跳跃运动为主 ,在河床上形成沙波形态 ,并发育良好 ;其河床沙波的形成、发展和消失与河床沉积物颗粒度特征和涨落潮水流强弱息息相关。

受支流入汇作用主河推移质运动演化特征试验研究

天然河流中存在着大量的主支交汇河流,在主支流相汇处,由于河相关系的变化,主支河流原有的水沙平衡状态被打破。通过一系列的水槽试验研究了交汇角为30°时支流来水、来沙对主流输沙特性的影响,获得了在支流有无来水、来沙时不同主支汇流比下的主河输沙率和累积输沙量随时间演化过程。试验表明:单一主河推移质呈“波”状输移,具有时空不连续性;支流仅来水时,由于无泥沙补给,交汇口及其下游会形成冲刷深槽,主流输沙率和输沙量强度在初始阶段很大,随着时间的推移,其值逐步衰减并趋于稳定;支流来水又来沙时,主河输沙特性与主支汇流比密切相关。

山区河流浅水条件下漂石对河床响应与泥沙补给影响的试验研究

受暴雨洪水与滑坡、泥石流灾害的影响,山区河流床沙多为宽级配卵砾石泥沙,甚至出现较多的漂石,从而影响近底水流结构与推移质输移特性。基于野外漂石河流的调查,通过概化水槽试验,探讨了漂石颗粒对河床冲淤的影响;对比分析了不同水沙条件下漂石对推移质输沙率过程的影响;根据床面粗化程度与漂石状态相异的两种类型对比试验,探讨了漂石对不同水沙条件下推移质输沙率的影响程度。研究表明:随着漂石颗粒相对淹没度(h/D,平均水深与漂石有效直径之比)的减少,漂石对其尾部区域水流的混掺越加突出,从而对河床的冲刷能力变大;根据本试验采用的水沙参数,漂石对推移质输沙率的扩大效应为几倍至十几倍。