Characteristics of gully bed scour and siltation between check dams

Check dams are the most commonly used engineering measure for debris flow control worldwide.The scour and siltation characteristics between dams are important factors affecting dam design.In this study,classical dimensional analysis of the variables that influence the development of gully bed scour and siltation was carried out.Flume experiments were conducted to examine the influence characteristics of opening width,flume slope,debris flow density,and opening rate on the characteristics of gully bed scour and siltation.The influential characteristics of variables on the dimensionless scour depth,scour length,siltation length,scour volume and siltation volume were obtained.The experiments showed that,with an increase in the relative opening from 1.5 to 2.5,scour depth increased by 7.4%,scour length decreased by 11.2%,siltation length increased by 22.0%,scour volume decreased by 4.7%and siltation volume increased by 22.0%.With an increase in flume gradient from 0.105 to 0.213,scour depth,siltation length and siltation volume increased by 40.0%,65.9%and 65.9%,respectively,and scour length decreased by 20.1%.With an increase in sediment concentration from 0.303 to 0.545,siltation length and siltation volume increased by 15.4%and 15.4%,respectively,and scour depth,scour length and scour volume decreased by 9.6%,9.1%and 17.8%,respectively.As opening rate increased from 0.08 to 0.32,siltation length and siltation volume increased by 33.3%and 33.3%,respectively,and scour depth,scour length and scour volume decreased by 5.4%,13.7%and 18.4%,respectively.The results showed that the flume gradient was the most influential factor on scour depth,scour length,siltation length and siltation volume,and the sediment concentration was the most influential factor on scour volume.Then,according to the experimental data,some empirical formulas predicting scour depth,scour length,siltation length,scour volume and siltation volume were obtained.The error between the computed values according to the formulas in this paper and the observed values was within±10%.These research results may provide a technological basis for window dam design in debris flow disaster prevention and mitigation.

A Siltation Simulation and Desiltation Measurement Study Downstream of the Suzhou Creek Sluice, China

The Suzhou Creek Sluice is currently the largest underwater plain gate in the world, with a single span of 100 m. It is located in a tidal estuary at the junction of the Huangpu River and Suzhou Creek in Shanghai, China. In this study, physical and 2D vertical mathematical models were used to investigate and distinguish the mechanism of siltation downstream of an underwater plain gate from that of other gates types. According to quantitative data obtained by site investigation and the application of the physical hydrodynamic models, it was found that the characteristics of the tidal estuary as well as the fact that the sluice span is equal to the creek width are the major reasons contributing to siltation. A possible desiltation treatment system is proposed for the underwater plain gate. The system includes selection of a suitable location that allows the determination of a reasonable top elevation of the sluice floor, reserving sufficient space under the gate to accommodate siltation, setting up a mechanical desiltation system, and flushing silt along with overflow over the top of the gate. Furthermore, on-site hydraulic silt flushing experiments and a topography survey were conducted. These results showed that the measurement system is effective, and by maintaining this scheduled operation once a month, the downstream riverbed has been maintained in a good condition.

Prediction of Siltation in the Downstream Approach Channel of Tidal Locks

Silt deposition occurs in the downstream approach channel of the tidal lock as in a closed channel or excavated dock basin. It is often difficult to calculate or predict siltation because of complex flow and sediment conditions and many other affecting factors. In this paper, the characteristics of flow movement in the approach channel (including its mouth) of the tidal lock are analyzed, the basic laws of sediment movement and siltation mechanism are investigated, the conditions for three types of siltation (circumfluence siltation, density flow siltation and slow flow siltation) are discussed, and corresponding calculating formulas are proposed. A practical example shows that the difference between measured and calculated results is small, indicating that the present calculating methods could be used in design and management of practical engineering projects.

Mechanism of back siltation in navigation channel in Dinh An Estuary, Vietnam

The Dinh An Estuary is one of the Nine Dragon estuaries of the Mekong River. An international navigation channel was built in the estuary for vessels traveling from the South China Sea to the southwestern area of Vietnam and then to Phnom Penh, Cambodia. The morphological evolution of the navigation channel is complicated and unstable. The back siltation intensity in the navigation channel has largely increased and been concentrated in the curvature segments of the channel since 1980. In this study, based on simulation results and measured data, five key factors that influence the back siltation in the navigation channel were systematically analyzed. These factors included the increasing elevation gap between the channel and the nearby seabed, the disadvantageous hydrodynamic conditions, sediment transport, mixing of saltwater and freshwater, and wave effects in the navigation channel. It is shown that the back siltation to a large extent results from the low current velocity of the secondary ocean circulation, which often occurs in the curvature segments of the channel. Suspended sediment also settles in the channel due to the decrease of the current velocity and the sediment transport capacity when flow passes through the channel. The changes of hydrodynamic conditions are responsible for the majority of the severe siltation in the curvature segments of the navigation channel.

Grey Prediction of Siltation in North Channel of Yangtze Estuary

-The North Channel in the Yangtze Estuary is one of sea-leading waterways of Shanghai Harbour, in which yearly dredging volume reaches over ten million cubic meters, and it tends to increase year by year. Based on the channel regime similarity and through the relational grade, a GM (2, 1) is set up. It reveals the course of development of channel regime similarity under the action of various factors, and predicts the siltation volume in the nearest future which is the basis of dredging planning for relevant dredging departments.

The influences of the tectonic subsidence and the siltation on the situation of preventing flood disasters in the Dongting Lake area

With the long-term data of the geodetic sea level measurements undertaken in the Dongting Basin and the recent sediment data of Dongting Lake, we analyze the tectonic subsidence rate of the Dongting Basin and the sedimentary rate of Dongting Lake. From the point of view of geomorphology and hydrogeology, we distinguish the two different spatial concepts between 'the basin of Dongting Lake' and 'the Dongting Basin'. Then, we discuss the influences of the tectonic subsidence and the siltation on the levees and the space of storing flood. The better quality of levees is required due to the tectonic subsidence and the siltation, and the difficulties of preventing flood disasters are increasing. The space of storing flood is not affected by the tectonic subsidence, but by the siltation. At present, the sedimentary rate of Dongting Lake is higher than the tectonic subsidence rate of the Dongting Basin. The tectonic subsidence capacity of the Dongting Basin counteracts a part of sedimentary capacity, and the shrinking tendency of Dongting Lake is restrained to a certain extent, but the tectonic subsidence is harmful to the situation of preventing flood disasters in the Dongting Lake area.

The siltation of debris flow behind check dam in the midstream of Bailong River

Siltation gradient and siltation length are important parameters for designing gravity check dams for debris flows,which directly affect the accuracy of estimates of interception capacity.At present,siltation gradient calculations are based primarily on empirical values,and range from 0.4 to 0.95 times the channel slope coefficient.The middle reaches of the Bailong River are one of the four areas in China that are most severely affected by debris flow hazards.Gravity dams are widely employed in this mountainous area.However,field studies of their capacity are lacking.In this paper,the operations of check dams were investigated.Based on field investigation results and theoretical analysis,calculations for siltation gradient,siltation length,and dam storage capacity are established.The impact of debris flow density,channel slope,and particle size weight percentages are discussed.The calculations show that the theoretical values for siltation gradient are consistent with measured values with 83.6% accuracy;and theoretical values of siltation length are consistent with measured values with 91.6% accuracy.The results of this research are an important reference for optimal height and spacing of dams,estimation of dam storage capacity,and disaster prevention.

Simulation and Analysis of Back Siltation in a Navigation Channel Using MIKE 21

The channel back-siltation problem has been restricting the development of channels,and its monitoring is limited by funds and natural conditions.Moreover,predicting the channel back-siltation situation in a timely and accurate manner is difficult.Hence,a numerical simulation of the back-siltation problem in the sea area near the channel is of great significance to the maintenance of a channel.In this study,the back siltation of a deep-water channel in the Lanshan Port area of the Port of Rizhao after dredging is predicted.This paper relies on the MIKE 21 software to establish the wave,tidal current,and sediment numerical models and uses measured data from two observation stations in the study area for verification.On this basis,taking one month as an example,the entire project channel was divided into five sections,and three observation points were set on each section.The results show that the area with offshore siltation is located in the northerly direction of the artificial anti-wave building.Siltation occurred on the northern seabed in the sea a little farther from the shore.Siltation occurred on the seabed surface far away from the shoreline,and with the increase in the distance from the shoreline,the amount of siltation in the south,center,and north became gradually closed,and the results can be used to guide actual engineering practices.This study will play a positive role in promoting the dredging project of Rizhao Lanshan Port.

Impact of PhaseⅢProject of Maji Mountain Port on sediment siltation in adjacent sea area

Based on a 3-D Finite Volume Coastal Ocean Model（FVCOM）, tidal dynamics has been studied in the sea area around the Phase III Project of Maji Mountain Port（MMP）. Furthermore, taking typhoon ＂Canhong＂ as an example, a storm surge and sediment model has also been established to study the impact of the Phase III Project on current flows and siltation during extreme weather. Tidal currents before and after the project have been compared. Model results show that the changes of tidal current mainly occur in the engineering areas with a magnitude change of 0.3–0.4 m/s during maximum flood and ebb tides. The flow condition for the port has been improved as the flow direction is changed to parallel to the wharf after the completion of the project. There is little siltation in the adjacent area, which will not affect the safety of ship navigation. Besides, the sudden siltation during typhoon period is relatively weak. The back silting in two days is less than 5 cm indicating no sudden siltation occurs.

Change of Back Siltation in Lianyungang Harbor before and after Completion of the West Breakwater

On the basis of a comparison of the field hydrological, sediment and topographic data observed before and after the completion of the West Breakwater in Lianyungang Harbor, which has led to the change of topography from a strait to a bay, a synthetical analysis is conducted on the change of back siltation. The results show that it is the change of coast line and the consequent change of hydrological condition and sediment movement that has led to the change of back siltation in the harbor. This phenomenon is caused by the lag effects of water current, sediment movement and local adjustment of topography after the construction, and it tends to be stable. The results of analysis provide not only a basis for extension of Lianyungang Harbor into a deep water harbor, but also propose a case for the study of the change of back siltation in a harbor on muddy coast.

A Novel Method for Real-Time Monitoring of Channel Siltation Based on Bistatic Scattering Theory

Monitoring the thickness changes of channel siltation is paramount in safeguarding navigation and guiding dredging, This paper presents a novel method for realizing the field monitoring of channel siltation in real time. The method is based on the bistatic scattering theory and concerned more with the receiving and processing of multipath signal at high-frequency and small grazing angle. By use of the multipath propagation structure of underwater acoustic channel, the method obtains the silt thickness by calculating the relative time delay of acoustic signals between the direct and the shortest bottom reflected paths. Bistatic transducer pairs are employed to transmit and receive the acoustic signals, and the GPS time synchronization technology is introduced to synchronize the transmitter and receiver, The WRELAX （Weighted Fourier transforul and RELAX） algorithm is used to obtain the high resolution estimation of muhipath time delay. To examine the feasibility of the presented method and the accuracy and precision of the developed system, a series of sea trials are conducted in the southwest coast area of Dalian City, north of the Yellow Sea. The experimental results are compared with that using high-resolution dual echo sounder HydroBoxTM, and the uncertainty is smaller than ＋ 0.06 m. Compared with the existing means for measuring the silt thickness, the present method is innovative, and the system is stable, efficient and provides a better real-time performance. It especially suits monitoring the narrow channel with rapid changes of siltation.

Second sea－entering approach of Changjiang River： Tongl Canal－planning of control dimensions， analysis of erosion and siltation and selection of outlet

Assume that the Tonglu Canal would be widened and deepened in which a water lock is constructed atthe river side, and made open to the sea side. The canal's planned control dimensions are determined, and the erosionand siltation characteristics along the river (totally 81. 8 km) are analyzed by the numerical calculation of one-dimen-sional unsteady flow and the relative standards. According to the data of the evolution, hydrology and sediment inthe Xiaomiaohong Waterway, it is found reasonable to select the channel near the Xingang Gate as the second sea-entering approach. This paper is helpful in planning and designing the approach.

Integrated Evaluation of Soil Erosion Hazard and Risk Management in the Oued Beht Watershed Using Remote Sensing and GIS Techniques: Impacts on El Kansra Dam Siltation (Morocco)

The initial state of the Oued Beht watershed (430,728 ha) is characterized by a socio-ecological vulnerability associated to the water erosion risk. Especially, the consequences are chained and the soil loss alters its hydrological behavior and its ability to protect functional and structural challenges (good land, El Kansra dam, agricultural activities). In this perspective, this study suggests a methodology, reproducible and generalizable, to assess the natural water erosion risk (R). The approach used is based on spatial processing technology of information to develop a spatial database and geographic information system (GIS) concerning biophysical and?topoclimatic parameters in the Oued Beht watershed. Thus, the risk analysis is obtained by combining thematic maps of Susceptibility (S) and potential Consequences (C). Although, the spatial analysis of maps obtained reveals the extent of susceptibility involving land degradation, with the potential risks, which generated a decrease in the storage capacity of El Kansra dam (?3.03 Mm3/year). The results show that erosion is active on more than three quarters (3/4) of the watershed, and a considerable loss of land with 8.36 Million tonnes per year. In this way, flood analysis and study of?hydrometeorological events identified the vulnerability of flood sites (hot-spot) contributing at 77%?of El Kansra siltation dam. Therefore, the consequence assessment is obtained by identifying risk elements and estimating potential damage coefficient, which represents the financial gap flow affecting the socio-economic context due to the erosion impacts.

Predicting Siltation in Entrance Channel Based on Wind Conditions

The siltation induced by wind waves in an entrance channel is one of the prime factors influencing the operation efficiency of a port. It is necessary to predict the siltation accurately for dredging and ship operation passing through the entrance of the port. However, it is difficult to apply the traditional method to predicting entrance siltation because of its complex computational procedure and lacking the data of ocean dynamic elements in the specified sea area. From the view of energy conservation, a direct relationship between wind conditions and sediment deposition can be founded. On the basis of the above methodology, an empirical formula expressed by wind conditions for forecasting the siltation in the entrance channel is set up. The wind conditions are easily obtained from the local meteorological stations or weather maps, so the formula established in this paper is more convenient and practical than the traditional method. A case study is provided, in which the emopirical formula is calibrated and verified utilizing the measured wind and siltation conditions in the entrance channel of the port. Comparisons between computed values and measured data show satisfactory aqreement.

Siltation Prediction for Navigation Channels and Harbour Basins on Muddy Beach (II)

5. Application and Popularization of Computational Methods for Siltation The above mentioned computational method covers siltation in navigation channels andharbour basins on muddy beach. This part mainly deals with the possibility of its application tosilty beach and sandy beach and the computation of scouring. The following discussion involvestwo aspects, and then some computational examples are given.

河湖库淤积治理中底泥清淤的内涵与发展方向

淤积问题对我国的水利事业影响深远,而底泥清淤是近些年淤积治理中经常采用的措施。针对底泥清淤的现状和存在问题,系统梳理了底泥清淤这一学科交叉领域的相关理论、技术和方法;阐述了对底泥清淤的概念、内涵、类型及基本问题的科学理解;提出了淤积治理中底泥清淤必须明确的四大问题:为什么治理、治理什么、用什么方法治理以及对后续产物如何处置。依据淤积对河湖库产生的危害,可分为物理性淤积、化学性污染和生态性损害三种类型。分别讨论了工程清淤、环保清淤和生态清淤间的共性和差异。对底泥清淤工程在目的、目标、手段及后续处理处置方面的现状及存在问题进行了评述。未来底泥清淤势必成为一个长期存在的工程和管理行为,因此更加高效、低投入、绿色、可持续的底泥清淤技术,是行业必然的发展方向。

三维水沙模型在航道减淤措施中的应用

山东滨州港港区于2015年11月经历一次大风骤淤过程,造成原有3万t级航道严重淤积,建设和发展滨州港,航道的骤淤治理是关键。基于三维潮流泥沙模型FVCOM及波浪模型SWAN,考虑水动力和泥沙间的相互作用,建立了基于新型三维辐射应力的三维水沙模型,依据2014年全潮水文观测资料对此三维水沙模型进行潮流场、波浪场及悬沙场的模拟和分析,验证了模型的可靠性,并计算了大风条件下现状航道淤积量和延长出水堤堤头位置至7.5 m方案和9.0 m方案的淤积量,分析了导致航道淤积的原因。模拟结果的对比论证表明,出水堤延伸越远,航道减淤量越大,但出水堤继续延伸后单宽减淤量会逐渐降低。本研究可为航道淤积治理及减淤措施设计等提供参考。

1300—2019年江苏沿海风暴潮灾害时空分布特征

历史上江苏沿海曾频发2类风暴潮灾害,给当地带来了巨大损失。建立该地区长时间尺度的风暴潮灾害序列对了解过去与预测未来意义重大。以历史文献、地方志、海洋灾害公报等记载的风暴潮资料为基础,建立了风暴潮灾害识别体系,重建了1300—2019年江苏沿海风暴潮灾害序列,分析了风暴潮灾害时空变化规律,探究了其与气候异常和黄河、长江入海口变迁之间的关系。结果表明:江苏沿海地区主要受台风风暴潮灾害的影响,1300—2019年间共发生246次风暴潮灾害,平均周期为2.9年,且近100年来发生频率有增大的趋势;小波分析结果显示,风暴潮灾害年际变化存在17年、61年和115年的时间尺度周期,其中115年周期最为明显。海气相互作用影响下,厄尔尼诺活跃年江苏沿海台风风暴潮灾害偏少;气温与台风风暴潮灾害频次有一定的正相关性,但其影响机制尚不明确。盐城、南通和苏州为风暴潮灾害高发地区,常州和无锡发生频率较小。在气候变暖与江苏海岸冲淤变化的作用下,1855年后盐城和南通地区风暴潮灾害发生频率增加,连云港地区明显增加;随着海岸线的变迁与长江河口的演变,镇江、扬州、泰州与苏锡常地区受风暴潮灾害影响减少。

六垛南闸闸下淤积加重原因及防淤减淤策略分析

江苏灌溉总渠六垛南闸近年来闸下河道淤积明显加重,通过实测资料分析近年来灌溉总渠水沙条件变化特征及闸下淤积加重的原因,认为潮波变形引起的河口不平衡输沙是闸下淤积的根本成因,近年来上游来水减少及河口侵蚀加剧是闸下淤积加重的主要原因。进而总结了潮汐河口闸下淤积的机理和关键控制因素,并结合挡潮闸冲淤调度实践,提出了六垛南闸闸下清淤的策略和措施,认为下泄流量对闸下河道冲淤平衡起着决定性作用,水力冲淤辅助机械扰动可以大幅提升清淤效率,可作为六垛南闸清淤的常规措施。

海勃湾水库库区淤积及排沙运用指标分析

为了减缓水库淤积,延长海勃湾水库的使用寿命,对水库运行以来库区的淤积情况和排沙运用指标进行分析。对库区纵向和横向淤积形态分析可知,库区淤积主要在前坡段和顶坡段,而且前坡段和顶坡段高程1075 m以上的滩地已开始出现淤积;海勃湾库区泥沙淤积主要集中在排沙期7~10月,2014~2020年排沙期淤积泥沙占总淤积量的66%。高程1074 m以下是淤积的主体,淤积泥沙2.01×10^(8)m^(3),占总淤积量的95%。顶坡段断面D7~D20淤积量为1.82×10^(8)m^(3),占总淤积量的83%,是淤积的主要库段;确定排沙时段为7~10月;确定排沙量级为1500 m^(3)/s以上,但对于平枯水年可选1200 m^(3)/s以上进行排沙;确定排沙起始含沙量为2 kg/m^(3)以上可降低水位排沙;确定排沙期(7~10月份)的排沙调度水位控制在1071~1075 m,但当有合适的水沙条件时,可降低水位至死水位1069 m或以下进行敞泄排沙。通过对海勃湾水库库区淤积和排沙运用指标的分析,可参考这些排沙运用指标进一步制定详细的排沙调度方案。