Showing papers on "Siltation published in 2008"

Suspended sediment characterization and tracing using a magnetic fingerprinting technique: Bassenthwaite Lake, Cumbria, UK

Abstract: Robust identification of catchment suspended sediment sources is a prerequisite both for under- standing sediment delivery processes and targeting of effective mitigation measures. Fine sediment delivery can pose universal management problems, especially with regard to nutrient run-off and lake siltation. Here, 19 sus- pended sediment samplers were located within the three main tributary inflows to Lake Bassenthwaite, a key but vulnerable site of special scientific interest, with water quality problems linked to accelerated delivery of fine sediment. Magnetic properties of contemporary suspended sediments, collected on a monthly basis, were measured on a particle size-specific basis and compared with the lake sediment core-tops. Ferrimagnetic grain size and magnetic 'hardness' vary significantly between the suspended sediments collected from the different tributaries, with the 8-31 µm and 31-63 µm clastic grain fractions displaying greatest magnetic contrasts. Post- depositional formation of bacterial magnetosomes is evident in the 2-8 µm and < 2 µm fractions of the lake sediments. Thus, for comparison with the potential source suspended sediments, we use only the detrital, clas- tic fractions, 8-31 µm and 31-63 µm. The lake sediment magnetic properties show little spatial variation, indi- cating through-lake transport of sediment (no evidence was found of postdepositional diagenetic sulphide formation). Magnetic comparisons between the potential sources and the lake surface sediments indicate that Newlands Beck, providing only ~ 10% of the lake's hydraulic load, is the main contributor of sediment to the deep basin of the lake. Sediments from the River Derwent subcatchment, contributing ~ 80% of the hydraulic load, are possibly stored either on the floodplain or in shallower areas of the lake.

Research on cohesive sediment erosion by flow: An overview

Abstract: Erosion of cohesive sediment by flow is a very complicated phenomenon occurring worldwide. Understanding and modeling of the erosion process are important for many issues such as the breaching of embankments, riverbank stability, siltation of harbors and navigation channels, service life of reservoirs, distribution of (heavy metal) pollutants and water quality problems. In the last few decades, numerous studies have been done on the erosion of cohesive sediment by flow. Nevertheless, the factors affecting the erosion resistance of cohesive sediment are still not fully understood and the knowledge of the physics of cohesive sediment erosion is inadequate, as a result the mathematical modeling of this erosion is far from satisfactory. In this paper an overview of the studies on the erosion resistance, erosion threshold and the erosion rate of cohesive sediment by flow is presented. The outcomes achieved so far from the studies and the existing problems have been analyzed and summarized, based on which recommendations are proposed for future research.

Erosion and nutrient loss on sloping land under intense cultivation in Southern Vietnam

Abstract: To help improve the well-being of the local people, a joint Vietnamese-UK team set out to establish a way of estimating soil and nutrient losses under different land management scenarios, using field data extrapolated through remote sensing and GIS, to obtain catchment-wide estimates of the impact of land cover change. Immigration from remote provinces to the Dong Phu District of Binh Phuoc Province, about 120 km north of Ho Chi Minh City, has led to disruption of soil surface stability on easily eroded clayey sandstones, creating rapid nutrient depletion that affects crop yields and siltation in the channel of the Rach Rat river downstream. The poor farmers of the areas see crop yields drop dramatically after two or three years of cultivation due to the fertility decline. Soil loss varies dramatically between wet season and dry season and with ground cover. Erosion bridge measurements showed a mean loss of 85.2 t ha−1 y−1 under cassava saplings with cashew nuts, 43.3 t ha−1 y−1 on uncultivated land and 41.7 t ha−1 y−1 under mature cassava. The rates of erosion were higher than those reported in many other parts of Vietnam, reflecting the high erodibility of the friable sandy soils on the steep side-slopes of the Rach Rat catchment. However, although the actual measurements provide better soil loss data than estimates based on the parameters of soil loss equations, a large number of measurement sites is needed to provide adequate coverage of the crop and slope combinations in this dissected terrain for good prediction using GIS and remote sensing.

Estimating the suspended sediment yield in a river network by means of geomorphic parameters and regression relationships

Abstract: An application of regression relationships depend- ing on geomorphic parameters is proposed to predict the amount of the average annual suspended sediment yield at different sections of the drainage network. Simple and mul- tiple regression relationships, utilising the drainage density and the hierarchical anomaly index as independent variables, based on data from 20 river basins of different size located in Italy, are here tested. An application is also shown for a small river basin located in central Italy where it is possible to compare the obtained suspended sediment yield estimates with reservoirs siltation data. The results confirm the poten- tial applicability of regression equations for estimating the suspended sediment yield depending on the topological be- haviours of the river network. A discussion of the reliability of the method for ungauged basins is also provided, which puts in light the necessity of additional tests to support the application of the approach to small size watersheds.

A geomorphic approach for the ecological restoration of kaolin mines at the upper tagus natural park (spain)

Abstract: 3 CAOBAR S.A., Taracena, Guadalajara 4 Organismo Autonomo de Espacios Protegidos de Castilla - La Mancha, Guadalajara Abstract: The Upper Tagus Natural Park is one of the largest and most valuable protected areas in Spain (Guadalajara Province), and it overlaps with two protected habitats of the Natura 2000 network (a Special Protection Area for Birds and a Site of Community Importance). At the Outlying Protection Zone of the Park, and within the two protected habitats, a series of abandoned kaolin mines affect the aquatic habitats of the area by siltation of the fluvial network, being the main management problem of the protected areas. Active kaolin mines with operations preceding the declaration of the Natural Park (year 2000), although with reclamation plans, have also the potential of affecting the rivers by siltation. In this work, geomorphic criteria for the eco-hydrological reclamation of both abandoned and active kaolin mines are explained. The proposed landform designs point out that runoff and soil erosion can be reduced to the minimum by building composed concave slopes, whereas the highwalls' geomorphic activity is allowed to be active, although being controlled with drainage systems and retention trenches. It is also recommended that the layout of the reconstructed terrain resembles the local original surficial geomorphology. Finally, the construction of systems of flow control and sediment storage is proposed at the basis of the concave slopes (decanting pools, as small ecologically functional wetlands). For their gauging, the methodology of the International Erosion Control Association (IECA) will be developed. All that is made in a collaborative framework between Universities (UCM-UAH), the Natural Park managers, and one mining company of the area (CAOBAR S.A.) with environmental responsibility.

Erosion éolienne dans le Damagaram Est (Sud-Est du Niger) : paramétrisation, quantification et moyens de lutte / Wind erosion in the eastern Damagaram (South-East of Niger) : parametrization, quantification and control

Abstract: The 'cuvettes' of Eastern Damagaram (South-Eastern Niger), which are an important source of food and revenue, are being silted up by aeolian sediment. The amplification of the desertification phenomenon in the Sahel is exacerbating this process. The objective of this research, carried out to the North-West of Goure, was to evaluate the impact of land use on the aeolian activity and the silting up of the cuvettes on the one hand, and on the other hand to evaluate the effectiveness of a dune fixation technique in terms of flux reduction and ecological restoration. To achieve these objectives, the wind characteristics and the aeolian activity were monitored for three years and we measured the sediment fluxes in relation to the development of the herbaceaous cover. It was shown that sediment fluxes on pasture land follow clear seasonal dynamics related to the temporal dynamics of the aerodynamic roughness length (Z0). These dynamics are due to the impact of rainfall as well as pastoral and human activities on the herbaceous vegetation. Pasture land on sandy soils appears to be a potential source of sediment during the second half of the dry season and may therefore contribute to silting up of the cuvettes. The dust storms observed during the early part of the rainy season in the Sahel are responsible for an important mobilization of aeolian sediment. The physico-chemical analysis of the sediment indicates an increase in the clay and silt content relative to the sand content as the height increases above ground. This goes together with an enrichment in nutrients (N, P, K) and carbon. The mass balances at plot level are positive overall, thereby indicating a net addition of sediment, nutrients and carbon. However, the uncertainty associated with these mass balances is very high. Although the results seem to indicate the existence of external sources of sediment in the present study, they cannot be interpreted as a definite proof of the absence of erosion on grazed dune soils. The use of windbreaks made of Leptadenia pyrotechnica proved to be a very effective mechanical dune fixation technique, reducing sediment fluxes by more than 95% as off the first year. The windbreaks resulted in a progressive recovery of the herbaceous cover, both in quantity and species diversity. The herbaceous cover reinforced the anti-erosive effectiveness of the windbreak. This technique therefore constitutes an adequate method for the restoration of degraded dunes under zero grazing conditions.

Effect of suspended sediments on soil erodibility

Abstract: The soil erosion rate was studied on chernozemic soil samples with different densities in the flows with different contents of suspended sediments. It was shown that the soil loss was strongly reduced in the presence of suspended sediments. The reason was the silting up of interaggregate pores by sediments, which increased the forces of adhesion between aggregates and, hence, decreased the erodibility of the soil samples. An empirical equation was proposed to estimate the effect of suspended sediments on the erodibility of the soil.

Coastal erosion and its environmental effect in the Modern Yellow River Delta

Abstract: The coast of Modern Yellow River Delta belongs to silt muddy coast,and it is impacted together by the volume of water and sand of Yellow River and marine coastal hydropower,its erosion is serious and the change has obvious temporal and spatial characteristicIn 1976,the Yellow River changed its flow along Qingshuigou,the coast of Diaokou outfall,which is the old course of Yellow River,began to erodeAt the early years,the velocity of erosion is fast,recent ten years,the velocity is slower obviouslyTo the contrary,in the current outfall area occurs silting upSince 1990s,especially recent years,the sediment discharge in the Yellow River was becoming less and less,so the area of siltation is limited around of current course,and the erosion occurs at large area in coastAs a typical coastal wetland of China,the environment of Modern Yellow River Delta is degraded because of the erosionWe should systematically and roundly research the complexity of coastal erosion in order to establish an integrated management system to mitigate it and improve the environment of coastal wetland

The Effect of the Exceptionally Low Water Discharge on Sediment Characteristics of the Middle and Lower Yangtze River

Abstract: Based on meteorologic data, historical sediment data and current sediment data collected in October 2006 in the Yangtze River Basin, the analyses of monthly mean water and sediment discharge characteristics, meteorologic characteristics and the effect on suspended sediment concentration and suspended sediment grain diameter under the exceptionally low water discharge were carried out. The results showed that the sediment discharge decreased remarkably in the year of low water discharge, and the sediment discharge of flood season at Datong Hydrographic Gauging Station is only 19.8% of the mean value from 1985 to 2000. The mean suspended sediment concentration in October 2006 was 0.057 kg/m3 in the middle and lower Yangtze River, being only 20.6% of the mean value in October from 2003 to 2005. The mean suspended sediment median diameter in October 2006 was 4.8 m, being only 26.3% of the mean value of historic records and 41.8% of the annual mean value recently. The synthetic analysis of suspended sediment concentration, suspended sediment diameter and scouring/silting characteristics showed that the vertical water and sediment exchange was intense in the reach from Chenglingji to Hukou, where the channel adjustment has taken place frequently in recent years. Under the background of the exceptionally low water discharge and the completion of the Three Gorges Project, the contribution of the suspended sediment concentration from Dongting and Poyang lakes to the main stream was greater than that of any other lakes and tributaries, and the contribution of Poyang Lake was greater than that of Dongting Lake. The influence of the suspended sediment diameter from the Hanjiang River and Chaohu Lake to the main stream was greater than that of any other lakes and tributaries, while the influence of Dongting and Poyang lakes was relatively small.

Evaluating the collective performance of best management practices in catchments undergoing active land development

Abstract: D evelopment of land, particularly from forested and agricultural uses to urban and suburban uses, has been accelerating in recent years in South Carolina and throughout many other regions of the United States. Although it is relatively well known that such long-term changes in land use/cover can lead to subsequent adverse environmental and ecosystem effects, less recognized are the potential impacts on aquatic environments caused by the actual process of land development itself (e.g., removal of vegetation, disturbance of large areas of soil). For example, episodic and sediment-laden storm water runoff from construction sites can overwhelm the capacity of receiving streams and lead to streambed scour, stream bank erosion, destruction of near-stream vegetative cover, and loss of in-stream habitat for fish and other aquatic species. Furthermore, deposition of sediment in receiving streams over short periods of time from development activities can exceed natural sediment deposition occurring over several decades. The US Environmental Protection Agency has identified sedimentation/siltation as the second most frequently cited stressor of rivers and streams, and has also identified undeveloped areas undergoing active development as a major source of the sediment. The objective of our study was to determine whether best management practices (BMPs) implemented in study catchments …

Study on mathematical modeling for non-uniform sediment transport in an irrigation district along the lower reach of the Yellow River

Abstract: Based on the one-dimensional equations of flow and non-uniform sediment movement,a mathematical model is established to calculate the non-uniform sediment transportation and siltation in an irrigation canal system.The model has been simplified rationally,taking account of the characteristics of flow and sediment transport and the measured data in the irrigation canals.In the model,the modes of flow and sediment diversion and scouring and silting along canal systems are considered,the suspended sediment movement is calculated in terms of sorted particle sizes,the flow and sediment is simulated on the basis of divided sections of the canal.The model is verified with the measured data in the Bojili irrigation district in Shandong province.The results show that the model can be used to predict non-uniform sediment movement in irrigation canals under various conditions of incoming flow and sediment.

Classification of catchment risk areas using spatially distributed event-based soil erosion: a case of upper njoro river catchment, kenya

Abstract: Human-induced soil erosion and drastic change in land use practices have adversely infl uenced the land degradation and surface runoff response in upper Njoro River catchment. The drainage area is approximately 127 km 2 . Due to human activities, the land has been exposed to accelerated erosion and low land productivity, water scarcity, decline in ground water recharge, siltation of Lake Nakuru and other sediment sinks. This study was conducted to establish event-based risk areas for prioritized conservation within the catchment. Spatially distributed soil erosion map was created as a ratio of sediment yield to sediment delivery ratio (SDR). Modifi ed Universal Soil Loss Equation (MUSLE) integrated within a Geographical Information Systems environment was used to create the sediment yield map. Spatial data layers for the MUSLE were derived from a 20-m resolution Digital Elevation Model, soil property, land use maps and climatic data of the catchment. Land use map was derived from Landsat imagery via its processing using Integrated Land and Water Information Systems software. The results show that the spatially distributed soil erosion ranged from 0.06 to 0.51 t/ha for a 43.2-mm rainfall event. Spatially distributed SDR ranged from 0.09 to 0.82, while the average SDR for the whole catchment was 0.72. These values were derived using an empirical equation. A new contribution was made by developing spatially distributed slope length factor, SDR, runoff volumes, MUSLE parameters and classifi ed erosion risk areas for prioritized catchment conservation. This means that the event-based soil erosion classifi cation can be adopted for prioritized soil and water conservation within Njoro catchment.

Micro watershed to basin scale impacts of widespread adoption of watershed management interventions in Blue Nile Basin

Abstract: High population pressure, inappropriate agricultural policies, improper land-use planning, over-dependency on agriculture as source of livelihood and extreme dependence on natural resources are inducing deforestation, overgrazing, expansion of agriculture to marginal lands and steep slopes, declining agricultural productivity and resource-use conflicts in many parts of Blue Nile. Increased land degradation from poor agricultural practices and erosion results in increased siltation and the reduced water quality in the river basin. The rainfall, runoff and sediment are highly variable both in time and space. Poor water and land management upstream severely affect runoff characteristics and the quality of water reaching downstream. The result is a downward spiral of poverty and food insecurity for millions of people both within the upper catchment and downstream across international borders. Quantification of the erosion, sedimentation processes and evaluation of impacts of interventions are difficult tasks. This paper schematizes the Blue Nile Basin (BNB) at various spatial levels as micro watershed, watershed, sub-basin to basin. It is revealed that sediment in the river systems are temporally varying phenomenon and strongly related to the early onset of rainfall. The hydrographs of the systems shows that the peak of sediment reaches first followed by peak of rainfall and then runoff. Furthermore, the sediment cumulative curve shows that most of the sediment volume passes in the river in the first three months of the rainy season. The paper also considers a particular watershed to model runoff, sediment and impact of watershed intervention. The result shows that runoff can be reasonably simulated with calibration of R2=0.87 and validation of result of 0.82, and comparable sediment modelling results. The study also demonstrates, by undertaking spatial analysis using topographic, soil and land use parameters it is possible to identify the high sediment risk sub-watersheds. Impact of typical watershed intervention using various widths of vegetative filter and application on high erosion risk watersheds shows reduction of sediment yield from 52% to 74%.

Ecological and environmental problems of the Chaohu lake and countermeasures

Abstract: Three are 3 main environmental problems in the Chaohu lake: lake eutrophication caused by nitrogen,phosphorus pollution;lake siltation caused by soil-water loss;natural disaster caused by meteorological, geological and biological disastersIn the light of the mentioned problems,the relative countermeasures are suggested: to control discharge amount from pollution sources,to promote clean production technology,to transfer economic growth mode;promote industrial structure change from sources-type to quality-benefit-type,to adopt ecological project measure for the lake,to dredge bottom mud,to plant terrestrial plant on floating-bed for water purification,to construct vegetation belt on the lake shore,to harness basin environment,to plant ecological conservation afforestation,to increase forest covering ratio,to strengthen administrative management,to raise environment protection sense of publics and perfect relative laws and regulations

Transverse and Longitudinal Eigenfunction Analysis of a Navigation Channel Subject to Regular Dredgings: The Adour River Mouth, France

Abstract: The Adour river mouth is located in Anglet, on the southwest coast of France, and it provides access to the commercial harbour of Bayonne. The navigation channel suffers from a recurring problem of silting and needs regular dredging. The construction of breakwaters and jetties has not solved the silting problem. Recently, a preventive trench was dug south of the channel to decrease the rate of siltation in the navigation channel. Bathymetric data of the river mouth were monitored for 26 mo, and 40 bathymetric sets of data were analysed. During the investigation period, four dredging campaigns were carried out. The surveys provide a very unusual bathymetric record because the sampling in time is extremely dense for such data. Eigenfunction analysis was performed along transects perpendicular and parallel to the direction of the river flow. These analyses are usually used to explain natural bathymetric or topographic evolutions. Here, there are also used to describe anthropogenic influences. The fi...

Influence of Construction of Artificial Island in Rudong,Jiangsu,upon Hydrodynamics,Erosion and Siltation in Surrounding Water Areas

Abstract: To build a shoal water artificial island in Fushe Sand Cay in South Yellow Sea where the hydrodynamic and sediment environment is considerably complex,we should not only consider carefully the stability of the artificial island itself but also made in-depth studies to investigate if the flow field and deposit of sedimentation resulted from the construction of the artificial island would change greatly the present tidal current hydrodynamic field and the systematic situation of "waterway-sand cay"and if the trend pattern of natural evolution would be accelerated or reversed owing to the construction of the artificial island.Integral physical modeling of tidal currents and sedimentation was made to investigate the influence of the construction of Xitaiyand Sand Shoal Artificial Island upon the trend of evolution of the furrow and the short-term fluctuation of the erosion and siltation in the construction area as well as the pattern of change of the hydrodynamics,erosion and sedimentation around the artificial island after the completion of Rudong Artificial Island.Corresponding measures against erosion have been proposed.The results of the model tests show that the hydrodynamic change of the water current resulted from the proposed artificial islang occurred mainly in the shoal water area close to Xitaiyang Sand Shoal and within a range of 1.5 diameter of the artificial island,imposing no influence on the tidal current hydrodynamics in the deep trough of the nearby waterways.The construction of the artificial island has not changed the pattern of the tidal hydrodynamic field in the waterways around Xitaiyand Sand Shoal and has neither resulted in the increase of the tidal hydrodynamics in this waterway but decrease in another nor changed the hydrodynamic sediment environment which controls the evolution of the"waterway-sand cay"system at Xitaiyang Sand Shoal.The stability of the core of Xitaiyang Sand Shoal rests mainly with the natural evolution process that makes the tidal hydrodynamics increase in the north of Xitaiyand Sand Shoal.So far as the construction of the artificial island is concerned,effective measures to protect the apron against erosion in front of the northeast walls of the artificial island will play the positive role in stabilizing the core of the sand cay and cutting down the source of sediment to deposit in the deep trough of the northern waterway.

Evaluation of potential of floodwater utilization in the middle and lower reaches of the Weihe River

Abstract: Water shortage,flood prevention and disaster mitigation are important problems awaiting to be dealt with in the Weihe River of Shaanxi Province.Under this situation,floodwater utilization would become an important way to realize comprehensive management of resources and the sustainable development of regional economy.In Guanzhong area which is located at the lower reaches of the Weihe River.The Weihe River is the biggest branch of the Yellow River,passing through Gansu,Ningxia and Shaanxi provinces.The middle reaches of the Weihe River is located in Shaanxi Province,with broad water ways,many shoals and scattered water flow.The lower reaches of the Weihe River is located in Xianyang,with serious channel siltation and small gradient.The flood resulted from heavy rain is the major disaster in these two areas.In general,the floodwater takes up about 33.1%-39.3% of the total runoff annually;the silt is about 60.1%-74.3%,where all data are mean values.It can be seen that a great deal of water and silt comes from the floodwater.By analyzing features of water,the quantity of silt coming from the upper reaches of the Weihe River,and the channel siltation,we establish the criteria as the initial values to evaluate the floodwater utilization;that is,the flood peak with a velocity of 2000m3/s in the middle reaches of the Weihe River,and that of 3000m3/s in the lower reaches of the Weihe River.According to these criteria,based on calculations we obtain the annual average quantlity of the available floodwater and silt from Linjiacun to Wijiabao is 4.038×107m3,and 6.83×106 t respectively,the quantlity of the available floodwater and silt from Weijiabao to Xianyang is 9.139×107m3,and 6.05×106 t respectively,and the quantlity of the available floodwater and silt from Xianyang to Huaxian is 1.617×108m3,and 1.843×107t,respectively.It is necessary to establish the risk management system to gain the optimal effects of flood prevention,water supply and ecological protection.

Geotechnical Survey, Dredgeability Of Soil Sediments And Siltation Volume Of Brimsu Water Reservoir

Abstract: The water supply for the Cape Coast Metropolis of Ghana comes from Brimsu reservoir. The accumulation of soil sediments in the reservoir since construction and commissioning in 1928 has resulted in a drastic reduction of the storage capacity of the reservoir leading to perennial water shortages to the community. A dredging syst-em to desilt the sediments and to improve the storage capacity was investigated. The volume of siltation was determined by hydrographic and topographical surveys using Global Positioning System and Total Station Tec-hniques to obtain data on the area and thickness of the sediments. The rate of siltation had more than doubled since the construction. The geotechnical characteristics of the sediments showed the sediments were of unifor-mly graded sand with admixtures of clay and silt. The dredgeability of the sediments was characterized by geo-technical descriptor terms, indicating that the sediments could be dredged using cutter-type dredger for excava-tion, and transported by hydraulic pipelines to disposal sites. The study established that sustainable environme-ntal management is required to minimize the siltation of the reservoir and ensure regular water supply. Journal of Applied Science and Technology Vol. 12 (1&2) 2007: pp. 71-77

Prediction of Sediment Concentration in Open Sea and Siltation in Approach Channels to Lianyungang Port

Abstract: In domestic researches on the silting intensity in approach channels on muddy coasts,measured data of near-shore suspended sediment concentration(SSC) can be easily obtained but it is often quite difficult to acquire the SSC in the open seas.It is proposed that the siltation in approach channels can be predicted by the application of Liu Jiaju's equation for siltation in waterways and the SSC in the open seas is derived with the calibration of the near-shore empirical coefficient on the basis of the measured data of siltation in channels and near-shore sediment concentration.The calculated siltation in the approach channels fitted well the measured data as compared with the verification measurements made on the approach channels for ships up to 70 000 dwt in Lianyungang Harbour,on the basis of which,a prediction was made of siltation in the approach channels proposed to build for ships up to 150 000 dwt in Lianyungang Port.The result of the research showed that the proposed method of prediction is practicable and the calculated results are rational and authentic,which may be of reference for the calculation of siltation in approach channels under similar conditions.

Sand movement of silt-sandy beach and the outer navigation siltation

Abstract: In this paper,the sediment movement characteristics of silt-sandy beach and features of the outer navigation siltation are analyzed.Aiming at the three movement forms of suspended sediment,flow load and bed load in silt-sandy beach,the three-layer mode for the outer navigation siltation calculation is put forward,and the practical formula for calculating siltation of flow load close to sea floor is deduced,then the practical formula applying to the outer navigation siltation of silt-sandy beach is established.According to the on-scene actual measurement data,strong windy siltation which happened in Huanghua is calculated and compared with the on-scene measurement data.The result shows the tendency is unanimous and the grade coincides.The formula can be popularized and used.

Research on Hydrodynamic Conditions and Siltation in Outer Channel of Tianjin Port

Abstract: By using wind,wave,tidal current,sediment numerical models based on the up-todata hydrology,sediment data of field observation and remote sensing data,sediment siltation in the deep channel is computed.According to the hydrological and sediment data of field observation in recent years,statistical analysis is done for the research and the parameters for the numerical model is provided.By building up the multiple nested tidal numerical models,current field before or after the execution of a project under regular weather is simulated.By building up the wind-wave numerical models of the sea and the sediment transport model,wave,tide and sediment models are coupled.The yearly averaged sediment concentration is first computed under the wind and wave action,then the sediment siltation is computed and the annual deposition distribution is also obtained after the channel is built.This paper proposes the characteristics of the deposition distribution in the deep channel after the south and north breakwaters extend to 16+0 km and provides design basis for the excation of the channel.

Study on hydraulic geometry from Jieshou in Xijiang River

Abstract: Based on the research and application experiences about the fine reach and hydraulic geometry in waterway engineering,a method to select fine reaches was proposed if not enough erosion and siltation data areavailableBeing applied on the river reach from Jieshou in Xijiang River,lots of fine reaches were selectedand their hydraulic geometry formulation under waterway regulation water level was successfully establishedThe research resultscan be used in waterway regulation planning

Application of siltation promotion and erosion control technique to river regulation and beach reclamation engineering in Yuyao

Abstract: As to the river reclamation of Yuyao,the most important key techniques are how to construct siltation dikes.According to the sediment deposition and flow characteristics in different areas,different erosion control methods were used.In high,medium beach laying of geotextile fabric,filled geotextile bags are used in lower beach,sand ribbed soft mattress can be used in the deep water zone.Though these kinds of measures,the foundation erosion can be reduced effectively,the dike construction speed can be improved.At the same time,the project investment can be saved substantially.

Sediment Transport and Changes in Scour and Silting in the Quanzhou Bay

Abstract: In this paper,the grain size trend analysis method is used to study the net sediment transport trend in the Quanzhou Bay,the sedimentation rate in the north channel of this bay is determined by using 210Pb dating method,and the changes in scour and sitting in this bay are calculated by means of comparison between nautical charts.It is shown from the study results that the Quanzhou Bay was generally in a siltation state,but the scour and siltation distributions in this bay were uneven,that is,the north channel was heavily silted with the upper reaches of north channel being the modern sedimentation center of this bay,and the south channel became the main pathway for sediment to transport out of this bay,and slight scour occurred in some areas of south channel.The horizontal differentiation between flood flow path and ebb flow path and the constraint of topographic conditions are main causes for siltation in the north channel,and the strong ebb current and runoff are main dynamical conditions for the south channel to become the main pathway of sediment transport.

Mathematical modelling of flow dynamics of the urban river nevezis in kedainiai

Abstract: The dynamics of flow velocities and water level in the Nevėžis River in Kėdainiai was estimated by applying a hydraulic-mathematical model DELTA. It was established that there were no conditions for a non-desirable riverbed siltation. During the dry season flow velocity in the examined section does not exceed 0.5 m/s. When the discharge Q=70 m 3 /s affects the formation of the riverbed, the flow velocity reaches 1.2-1.3 m/s and accumulated bed sediments are washed away. A two- meters high dam near Skongalis does not stimulate bed silting too, because it is not high and it can barely influence bed formation processes or reduce the riverside overgrowth. When the water level is low and the flow velocity is small (0.1 m/s), the water in the river is only slightly turbid (turbidity is 2-6 mg/l). In order to improve the esthetical view of the river, it is advisable to regulate the riverbed by reducing the river width at its wide sections up to 30 m.