Showing papers on "Siltation published in 2009"

Sedimentation in the Three Gorges Dam and the future trend of Changjiang (Yangtze River) sediment flux to the sea

Abstract: . The Three Gorges Dam (TGD) on the upper Changjiang (Yangtze River), China, disrupts the continuity of Changjiang sediment delivery to downstream and coastal areas. In this study, which was based on 54 years of annual water and sediment data from the mainstream and major tributaries of Changjiang, sediment deposition induced by the TGD in 2003–2008 was quantified. Furthermore, we determined the theoretical trapping efficiency of the cascade reservoir upstream of the TGD. Its impact on Changjiang sediment flux in the coming decades is discussed. Results show that about 172 million tons (Mt) of sediment was trapped annually by the TGD in 2003–2008, with an averaged trapping efficiency of 75%. Most of the total sediment deposition, as induced by the TGD (88%), accumulated within the region between the TGD site and Cuntan. However, significant siltation (12% of the total sediment deposition) also occurred upstream of Cuntan as a consequence of the upstream extended backwater region of the TGD. Additionally, the Changjiang sediment flux entered a third downward step in 2001, prior to operation of the TGD. This mainly resulted from sediment reduction in the Jinshajiang tributary since the late 1990s. As the cascade reservoir is put into full operation, it could potentially trap 91% of the Jinshajiang sediment discharge and, therefore, the Jinshajiang sediment discharge would most likely further decrease to 14 Mt/yr in the coming decades. Consequently, the Changjiang sediment flux to the sea is expected to continuously decrease to below 90 Mt/yr in the near future, or only 18% of the amount observed in the 1950s. In the presence of low sediment discharge, profound impacts on the morphology of estuary, delta and coastal waters are expected.

Impacts of maintenance channel dredging in a northern Adriatic coastal lagoon. I: Effects on sediment properties, contamination and toxicity

Abstract: Conservation and management of coastal lagoons envisage direct human intervention. To prevent siltation and to preserve the hydrodynamics features of the lagoon system, the inner channels undergo regular maintenance dredging. Sediment properties (RDP, organic matter, grain size), trace metals (Cd, Cu, Cr, Hg, Ni, and Pb), and toxicity vs. the amphipod Corophium insidiosum and the luminescent bacterium Vibrio fischeri, were analysed before and after dredging operations in a coastal lagoon (Pialassa Baiona, Italy). To detect the actual impacts, disturbed sites were contrasted with multiple controls in two distinct times, i.e. before and after disturbance, according to a sampling design based on Beyond BACI principles. The integrated methodology here adopted suggests that dredging operations carried out are not likely to pose dramatic effects on environmental quality of the lagoon.

Assessing sediment inputs to small reservoirs in Upper East Region, Ghana

Abstract: Many small dams and dugouts have been constructed in the Upper East Region of Ghana to address the problem of regional water scarcity. The reservoirs were constructed primarily as water supplies for agricultural irrigation and livestock watering, aquaculture and domestic use. However, many of the reservoirs dry up during the dry season, affecting the livelihoods of their basin inhabitants. A major cause for the dried reservoirs is siltation, which reduces the reservoir’s storage capacities. The goal of this study is to quantify the annual siltation rate of four study reservoirs, using a bathymetric survey and reservoir soil sampling. The sediment yield and its relation to catchment area also were assessed. The results of this study indicate that the annual siltation rates are 1272, 3518, 2764 and 6135 t year )1 for Doba, Dua, Zebilla and Kumpalgogo reservoirs, respectively. Analyses of the sediment yield and catchment areas illustrated that the sediment yields decreased with increasing catchment area. All the study reservoirs have lost their dead storage capacity, which was meant to store sediment until the end of their anticipated design lives. The decreasing storage capacity because of siltation will affect the livelihoods of the local basin inhabitants, as the reservoirs will not be able to achieve all their intended purposes. The results of this study indicate that, because siltation is not the only factor threatening the benefits gained from the reservoirs, the integrated assessment of all relevant factors is required.

Coastal erosion in response to wave dynamics operative in Sagar Island, Sundarban delta, India

Abstract: Coastal erosion at Sagar Island of Sunderban delta, India, has been critically studied. The area is in the subtropical humid region. There are mainly three seasons viz: winter, summer and the monsoon. Different wave dynamic parameters were measured from theodolite observations with leveling staff and measuring gauges during lunar days at two sections of the western and eastern parts of the coastal zone during post-and pre-monsoons. A comparative study was made on the erosion/depositional pattern between the two sections in relation to different hydrodynamic parameters prevailing in these two sections. Plane table mapping was carried out to demarcate the different geomorphic units. The marine coastal landforms show dune ridges with intervening flats bordered by gently sloping beach on one side and a flat beach on the other side. The western part of the beach is mainly sandy; whereas the eastern part is silty and clayey with mud bank remnants. Actual field measurements indicate that the coastal dune belt has retreated to the order by about 20 m since 1985. The eastern part of the beach has lowered by about 2 m since 1985 and the western part was raised almost to the same tune. It is observed that accretion in the western and central parts of the beach took place; whereas severe erosion in the eastern part made the beach very narrow with remnants of mud banks and tree roots. Frequent embankment failures, submergence and flooding, beach erosion and siltation at jetties and navigational channels, cyclones and storm surges made this area increasingly vulnerable.

On harbour siltation in the fresh-salt water mixing region.

Abstract: In this paper a novel series of field measurements are presented, which are the first to elucidate the processes influencing siltation in Botlek Harbour. Botlek Harbour is situated at the limit of saline water intrusion in the Rotterdam Waterway. Normally, after the ebb tide fresher river waters are found in the Rotterdam Waterway at the location of Botlek Harbour. On the flooding tide, the tip of the salt wedge is advected along the Rotterdam Waterway towards the mouth of Botlek Harbour. Hence on flood, a lock-exchange mechanism operates between Botlek Harbour and the Rotterdam Waterway. On the flood tide, when there is a supply of suspended particulate matter (SPM) associated with the presence of the estuarine turbidity maximum (ETM) at the mouth of the harbour, the survey data show exchange of SPM into the harbour. This lock-exchange process is found to be the dominant cause for SPM transport into the harbour. This is further substantiated by an analysis of the mass transport mechanisms. In this analysis, the vertical profiles of the instantaneous velocity, salinity and SPM concentration fields, recorded during the surveys, were decomposed into advective and dispersive transport components. The results of this analysis indicate that the correlation between the lock-exchange mechanism on the flood tide with the availability of SPM for exchange and efficient trapping, dominate the total exchange of SPM (97%). Hence, the increase in measured near-bed SPM concentration within the harbour is ascribed to tidal advection of saline water and the ETM along the Rotterdam Waterway. Tidal advection controls the density difference between the estuary and harbour, as well as the availability of SPM for exchange at the entrance to Botlek Harbour. The location of the ETM at the tip of the salt wedge is a key factor in supplying SPM to Botlek Harbour. Consequently the timing of the availability of SPM at the mouth of the harbour needs to be considered in siltation studies. The survey data suggest that Botlek Harbour basin has a 100% trapping efficiency. Analysis of 5 months of data, from a measuring rig located within the harbour, show excursions of the limit of the salt wedge and ETM. These excursions are likely to affect siltation of upstream harbours. Salinity-induced density gradients control the transport and subsequent trapping of SPM in the estuary in close proximity to the harbour entrance, the exchange of SPM between the estuary and harbour, and the trapping of SPM in the harbour basin.

Dynamics of sedimentary environments in the accelerated siltation of a reservoir: the case of Alhama de Granada, southern Spain

Abstract: An analysis has been made of sedimentary systems involved in the rapid silting of a reservoir constructed in 1974 in Alhama de Granada (S. Spain); in only 30 years the storage capacity of the reservoir has shrunk by 80% and its perimeter has decreased by 64%. A study of sediment lithofacies identified in a series of shallow trenches and of georadar facies identified in a series of almost 900 m lines of ground penetrating radar (GPR) images, together with a survey of surface geology, has identified 3 alluvial systems (2 transversal systems and a longitudinal system) whose deltas have filled in the reservoir. Thus, there are three phases in the evolution of the reservoir siltation: (1) an initial stage (1974–1977) typified by northward progradation of the longitudinal river delta of about 100 m year−1 and an eastward progradation of the transversal system delta of about 20 m year−1; (2) an intermediate stage (1977–1984) in which the longitudinal river delta progradation slowed to 25 m year−1 and the axial drainage became obstructed due to the considerable eastward progradation of the transversal delta; and (3) a final phase (1984–present) in which there have been few changes in the areal distribution of the deltas apart from a southeastward expansion of the transversal delta. Generally, aggradational growth patterns (vertical accretion) have dominated in this final phase. The lithology of the source area, the slope and precipitation distribution has a significant effect not only on the sediment supply, but also indirectly on the creation of accommodation space and on the evolution of stratal growth patterns.

SEPAL – a simple GIS-based tool to estimate sediment pathways in lowland catchments

Abstract: . Even though soil loss in the lowlands imposes not as much a restriction on land use and agricultural productivity as in erosion affected mountainous areas, the input of fine sediment into the rivers and streams is a concern due to water quality issues and substrate siltation. Drains, river banks and agricultural fields are the three main sources of fine sediment in lowland regions. For a successful implementation of measures to decrease sediment input a well-founded knowledge of the individual entry pathways is essential. To assess the importance of possible entry pathways, a GIS based methodology (SEPAL) has been established combining the ABAG, a river bank erosion formula and a regression approach to include the contributions of drains. SEPAL has been applied on a study catchment in Northern Germany. The results show that 15% of the sediment input into the river comes from agricultural drains, 71% from river banks and 14% from adjacent fields. A comparison of the results with field-mapping and -sampling shows that the approach is plausible. The calculated total annual sediment input is 616 t yr−1, while the measured suspended sediment load is 636 t yr−1. It can be concluded that the methodology is suitable for estimating sediment entry pathways and annual sediment loads in lowland catchments as a base for modelling projects and further investigations. However, further work is necessary for gaining sound knowledge about uncertainties and especially about the processes forcing sediment input from drains.

The Variation Process of Water and Sediment and Its Effect on the Yellow River Delta over the Six Decades

Abstract: In order to find out the variation process of water and sediment and its effect on the Yellow River Delta,this paper,by means of statistics,analyzed the water and sediment discharge from 1950 to 2007 at Lijin and the reduction of water and sediment in Yellow River Basin caused by human activitiesResults show that the water and sediment discharge into sea decreased from 1950 to 2007 with serious fluctuationThe human activities were the main cause for the reduction of water and sediments into seaFrom 1950 to 2005,the multiyear average reduction of water and sediment by means of water and soil conservation were 202×109 m3 and 341×108 t,respectively,while the multiyear average usage of water and sediment for industry and agriculture were 252 × 1010 m3 and 242 × 108 t,respectivelyFrom 1960 to 2007,the multiyear average sediment silted in the Sanmenxia Reservoir was 145×108 t and that silted in the Xiaolangdi Reservoir was 2398×108 tCompared to the data of Huayuankou,in the lowere reaches,the water and sediment discharge into sea decreased with siltation and increased with erosionThe coastline near the estuary extended and the delta increased when the ratio of total water and sediment into sea was about 00257 t/m3 in different periods

Water Erosion Modelling using Fractal Rainfall Disaggregation, a Study in Semiarid Tunisia

Abstract: In the Tunisian semiarid area, water erosion processes have led to negative economic and environmental consequences in a context of limited water resources. To characterize and predict these degradation phenomena, a comprehensive high-resolution data base on erosive rainfall, together with siltation records for 28 small reservoirs were analyzed. The studied small reservoir network displays a general life-span of about 14 years. The average soil loss is 14.5 tonnes/ha/year. The complex relationship between the erosive rainfall events and the annual soil loss rates can be explained by two important factors. The first factor is related to the soil “degradation cycle”. It determines the soil particle delivery potential of the catchment. The second factor corresponds to the “degradation front”. The latter presents a north-western/south-eastern direction. To investigate rainfall disaggregation possibilities, a regionalization of fine time-scale and daily rainfall was undertaken. The results showed that the spatial properties are typically non-isotropic. Clustering showed that two different homogeneous rainfall subgroups are closely related to the predominant convective and frontal rainfall types. The comparison illustrated important similarities between the maximum 15-min and the daily rainfall data. The above findings were an incentive to explore the multiplicative properties of a 4-year rainfall time series. The time series showed scaling behavior for time scales up to 100 min that coincides with the most active erosion process time scale. Moreover, the temporal structure of rainfall was reproduced using a disaggregation model (Olsson, 1998). The observed and generated rainfall time series displayed several similar characteristics. This allowed the reproduction of erosivity for erosive rainfall events longer than 45 minutes. The erosion modeling was performed using the USLE/GIS approach. Maps of observed and generated spatial erosion distribution were combined with the Masson’s and Wischmeier-Smith’s erosion limit intervals. According to the above, the potential of rainfall scaling-based approaches to predict water erosion levels in semiarid areas seems promising. Using this approach may help soil and water authorities in semiarid areas to better manage soil erosion problems. (Less)

Environmental degradation related to mining, urbanization and pollutant sources: Poços de Caldas, Brazil

Abstract: The paper considers the environmental problems associated with development within a volcanic depression at Pocos de Caldas, Brazil, which was undertaken without appropriate investigation and planning. Engineering geological mapping was carried out to characterize the area and identify the main environmental problems. The results allowed the division of the region into geological and geotechnical zones. Decommissioned and abandoned mines, agricultural uses, point and non-point pollutant sources and urban land use were identified as the main causes of erosion, siltation, soil and surface water pollution and changes in geomorphology, infiltration rates, groundwater recharge conditions, groundwater pollution, runoff and channel density.

Evolutional trend of the coastal wetland in Shanghai in response to decrease of sediment supply from the Changjiang River

Abstract: About 15% of the land needed for Shanghai's urban development came from the reclamation of the tidal flat of the Changjiang River delta over the last 50 years.Further reclamation is needed for Shanghai's urban expansion.However,due to damming,sand extraction and afforestation in the Changjiang River basin,there has been a decreasing trend for the riverine sediment into the East China Sea since 1960 s,which presents a threat to the source of the tidal flats for Shanghai that needs to be further examined.Based on the analysis of the series monitoring data since 1950,the amount of the riverine sediment delivery into the East China Sea and the general scour and silting trend at the outlet(shallower than 5 m isobath) of the Changjiang River Estuary in the next 20 years is estimated.The results show that:(1) The riverine sediment has greatly decreased by two thirds due to anthropogenic activities.The sediment load at the Datong Gauging Station has shown a decreasing trend since the late 1960s and it has been accelerated since the late 1980 s.The sediment discharge in the past 10 years(averaging 2.8 ×108 t/a) is only about 44% of that between 1956 and 1965(averaging 5.04 * 108 t/a).(2) The progradation rate of the tidal flats has been decreasing evidently.The combined progradation rate of East Chongming Shoal,East Hengsha Shoal,Jiuduansha,and East Nanhui Shoal was 19.1 km2/a between 1958 and 1977,5.1 km2/a between 1977 and 1986,and 4.9 km2/a between 1996 to 2004.(3) The area of the tidal wetlands above 5 m isobath at the outlet accounts for 70% of the total,in which East Chongming Shoal is 701 km2,East Hengsha Shoal 464 km2,Jiuduansha,410 km2 and East Nanhui Shoal 462 km2.(4) There is a linear correlation between the sediment load(108 t/a) at the Datong Gauging Station after taking the impact of the dredging activity in the North Passage into consideration and the progradation rate of the tidal wetlands(km2/a) at the outlet,that is,Y=9.5136X-29.05,R=0.925.Based on these results,it can be predicated that the sediment load at Datong will decrease to 1.5 ×108 t/a between 2006 and 2015 and 1.2× 108 t/a between 2016 and 2025.As a result,the tidal wetlands near the Changjiang River mouth may be eroded by 147.8 km2 between 2006 and 2015 and by 176.3 km2 between 2016 and 2025,which is about 6.3% and 7.5% of the present tidal wetlands respectively.The current Deep Waterway Project in the North Passage and the reclamation project at the East Hensha Shoal may hinder erosion in the future.If there are no further engineering protection measures to be taken,there will be a 10 % loss of total tidal wetland area in the next 20 years.The conclusion is as follows: due to the decrease in sediment load from the Changjiang River,the progradation rate of the tidal wetlands in the Changjiang River mouth has been decreasing and the tidal wetlands may be eroded in the future if there are no engineering protection measures to be taken.But the submerged delta may provide a source for sediment via resuspension resulted from flood tide erosion.If suitable measures are adopted to utilize the high suspended sediment concentration,Shanghai is expected to have new tidal wetlands for urban development.Further protection of the tidal wetlands and reclamation under high suspended sediment condition will secure the existing tidal wetlands resource and provide land for Shanghai's urban expansion.

Analysis of reasons for the siltation in North Passage of Yangtze Estuary

Abstract: In view of the characteristics that siltation in the deep waterway of North Passage has been increased and converged mainly on the middle reach since 2005,we analyze systematically the impacts from the change of various factors such as sediment and hydrodynamics,find out the major reason for the increase of back-siltation amount on the middle reach,and put forward an idea for working out the siltation-reduction measures.

Sahelian land-cover degradation and its effects on the silting-up of the middle Niger River

Abstract: In order to achieve the overall objective of this research which was to gain an understanding into the impact of land cover change on sediment production and transport in the middle Niger River basin, the application of various approaches was necessary. These approaches included the study of hydrological data (1929 – 2008) and land cover data (1965 – 2000), in addition to the measurement of sediment characteristics (2005-2008).The study focused on two Sahelian sub-basins (the Gorouol and the Sirba basins) in comparison to a Sudanian basin (the Mekrou basin). An evaluation of the evolution of land cover by remote sensing techniques showed an increase in disturbed bare soil surfaces favouring an increase of sediment transfer to the middle Niger via conventional tributaries as well as ungauged ephemeral streams that have increased in number and size since the 1970s. Field measurements of sediment characteristics where carried out at ten locations along the middle Niger River and some of its tributaries in order to quantify the sediment flux and sources in the study area. Hydrological analyses showed the impact of the reduction of precipitation on river discharge, with the most recent dry period, resulting in the alteration of the Niger River's regime at Niamey and affecting river planform. The sediment flux analysis for the middle Niger River points to the existence of other significant sediment sources apart from the main tributaries. A simulation of the sediment transporting capacity, by grain size class, using data from a 1-D model of the river enabled the localization of areas of sediment equilibrium and deposition, when compared to measured sediment concentration values.

Change of re-siltation in the Yangtze Estuary deepwater channel during 1~(st) and 2~(nd) stages

Abstract: The re-siltation change and its response to the incoming flow and suspended sediment at Datong station and the local width of 7m,8m isobath were studied by using the data of re-siltation in the Yangtze Estuary deepwater channel.Due to change of boundary conditions,re-siltation intensity of the whole navigation channel had an obvious decrease after implementing the Yangtze Estuary deepwater navigational improvements.The location of the maximum re-siltation intensity moved from the downstream during the 1st stage to the upstream during the 2nd stage.The re-siltation amount increased and moved downward in the flood season and decreased and moved upward in the dry season.There were several sources of sediment which resulted in re-siltation.The re-siltation won't be significantly reduced if only the suspended sediment load decreased.

Longitudinal suspended sediments transport in the jaguaribe river estuary, brazil

Abstract: The Jaguaribe River estuary lies in a region characterized by climatic irregularities, inserted in semi-arid terrains. These storms associated with climatic and anthropogenic processes entailed by a barrage construction, shrimp farms, mangrove deforestation and the use and occupation of margins, caused signifi cant changes in the processes of erosion, transport and deposition. These facts gave rise to economic losses and environmental impacts through the siltation of tidal channels and the less condition for navigability. Thus, it is important to know the mechanism of sediment production in order to contribute to the sustainable management of the activities to be developed. The study aimed to analyze the longitudinal transport of sediment in the river estuary based on data collection in situ through parameters of the hydrodynamic, morphodynamic and sedimentological conditions. Samples were collected in two tidal cycles (high /low tide). The analysis of longitudinal profi le revealed retention of sediments in the estuary during the rainy season. The fi ne material comes from the suspended loads from the inside of the basin and the contribution of the sandy-mud sediments of the Barrier Formation which borders the west bank of the estuary

A brief analysis of scour and silting of the tidal flats at the north bank of the Hangzhouwan Bay

Abstract: The estuarine bank is located at the transitional area between the river and sea,where the interaction of 4 spheres takes place and various interfaces meetThe coastal bank at the forefront of the estuary is the most sensitive zone of land-sea interaction and also the important land resource for the big cities in delta areaBeach scouring and silting is a kind of natural phenomena in estuary,the study of which is of great theoretical and practical significanceThe north bank of the Hangzhouwan Bay is at the south edge of the Changjiang River deltaWith the increasing need of the land resources,this area has got more and more attentionsMany scholars have studied this area and got a lot of valuable resultsHowever,in the past tens of years this area has experienced significant changes and many issues need to be studied in depthBased on the digitalized process of 4 maritime charts(1976,1993,1997,2004) with ARCGIS software,scouring and silting of the tidal flats at the north bank of the Hangzhouwan Bay is studiedThe results show that:(1) the Hangzhouwan Bay was scoured at the northern bank and silted at the south bank in the history,while the north bank has experienced scouring first and then silting;(2) because of inning at the northern bank,the shoreline has moved outward in the past 30 years;(3) in the past 30 the Nanhui section was mostly in siltation state before 1997 and in erosion state after 1997;the Jinshan section was mostly in steady state;the section from Jinshanzui to Jinshanwei was mostly in steady state;the section from Caojin to Jinshanzui experienced a process from erosion to siltation and then to erosion again;and the Fengxian section was in erosion state,but the erosion zone moved from the east to the west and also to the north in 1997~2004,the erosion moved from the tidal flat below-5 m to the tidal flat above-5 mThe erosion and siltation at the northern bank of the Hangzhouwan Bay is affected by many factorsBesides tide and storm,inning and the decrease of sand from the Changjiang River is two important factors resulting in the scouring of the bank

Experimental study on scouring and silting stability of the man-made beach in Dongjiang Harbor Area of Tianjin Port

Abstract: Experiments are carried out to study the sedimentation of the man-made beach in the east coast of Tianjin Port using the whole tidal current and sediment physical model and wave flume model.Since the coastal area of the project is a typical flow mud transfer coast,sedimentation in the intertidal zone of the hydrophilic section(about 5cm a year) is inevitable.Under the condition of sheltering,the man-made beach is basically stable under a 10-year wave.But under a 50-year wave,the deformation of the beach profile will occur,with the loss quantity in single width of about 3.3 m~3/m.

Spatial distribution of bottom sediment deposits in water reservoirs at Zeslawice

Abstract: Spatial distribution of bottom sediment deposits in water reservoirs at Zesławice Spatial distributions of bottom sediment deposits in two small water reservoirs located on the River Dłubnia at Zesławice is presented in this paper. The distribution was elaborated according to Dendy's method on the basis of results of silting measurements performed in the 2005. Horizontal and vertical distribution of sediment deposits was shown as relation between the relative volume of deposited sediments (Sh/S) and relative storage capacity of the reservoir (Vh/V); the vertical distribution of sediment deposits was presented as relation between the relative volume of deposited sediments (Sv/S) and relative reservoir depth (D/Dm). On the basis of performed analysis of horizontal distributions of sediment deposits it was stated that in the main reservoir at Zesławice 58% of the sediment trapped in the reservoir was accumulated in the inflow (upstream part of the reservoir, whose relative volume is 0.25). In the inflow section of the assistant reservoir of relative storage capacity equal 0.22 only 29% of the sediment was deposited. Comparing curves of horizontal sediment deposits distribution in the main reservoir in its inflow part according to measurement data from the 2005 and 1986 i.e. from a comparable period of operation before desilting and building of an assistant reservoir it was stated that relative volumes of sediment trapped after desilting are over 40% higher than before desilting. In a comparable period of operation before desilting (measurement in the 1983) and after desilting (measurements in the 2005) i.e. after seventeen and sixteen years respectively in the main reservoir the accumulated sediments formed an isle - the value Sv/S equaling 0.09 for D/Dm equal 0 in consequence of a change of hydraulic conditions of water and sediment flow - due to a part of inflowing water of the River Dłubnia being directed to the assistant reservoir. Rozkład przestrzenny osadów dennych w zbiornikach wodnych w Zesławicach. W pracy przedstawiono rozkład przestrzenny osadów w dwóch małych zbiornikach wodnych w Zesławicach na rzece Dłubni według metody Dendy'ego, opracowany na podstawie wyników pomiarów zamulania wykonanych w 2005 roku. Obliczony stopień zamulenia zbiornika głównego w szesnastym roku eksploatacji, po odmuleniu zbiornika głównego, wynosi 33,0%, a stopień zamulenia zbiornika remontowego w osiemnastym roku eksploatacji wynosi 18,8%. Określono poziome i pionowe rozmieszczenie osadów w zbiornikach. Poziome rozmieszczenie osadów określono jako zależność między względną objętością odkładów rumowiska (Sh/S) i względną pojemnością zbiornika (Vh/V), a pionowe rozmieszczenie osadów przedstawiono jako zależność względnej objętości odkładów rumowiska (Sv/S) i względnej głębokości zbiornika (D/Dm). Na podstawie analizy poziomego rozmieszczenia osadów stwierdzono, że w zbiorniku głównym w Zesławicach w części wlotowej zbiornika, której objętość względna wynosi 0,25, zgromadzone jest 58% rumowiska zatrzymanego w zbiorniku. W części wlotowej zbiornika remontowego o objętości względnej wynoszącej 0,22, odłożone zostało zaledwie 29% rumowiska. Porównując krzywe dystrybucji poziomej osadów w zbiorniku głównym w części wlotowej według danych pomiarowych z 2005 i z 1986 roku, tj. z porównywalnego okresu eksploatacji przed odmuleniem i wybudowaniem zbiornika remontowego stwierdzono, że względne objętości rumowiska zatrzymanego po odmuleniu są ponad 40% większe niż przed odmuleniem. W porównywalnym okresie eksploatacji przed odmuleniem (pomiar w 1983 r.) i po odmuleniu (pomiar w 2005 r.), tj. odpowiednio po siedemnastu i szesnastu latach, w zbiorniku głównym gromadzone osady utworzyły wyspę. Została ona utworzona w wyniku zmiany warunków hydraulicznych przepływu wody i rumowiska, spowodowanych skierowaniem części dopływu wód rzeki Dłubni do zbiornika remontowego, wartość Sv/S wynosząca 0,09 dla D/Dm równej zero. Stwierdzono, że zmianę rozkładu przestrzennego osadów w badanym zbiorniku wodnym umożliwia opracowany według Dendy'ego poziomy rozkład rumowiska w poszczególnych latach eksploatacji.

Impact on Discharge Capacity by Sediment-Runoff Regulation in downstream of the Yellow River

Abstract: Since 2002,the sediment-runoff regulation of Yellow River has persisted in 7 years,the flow capacity of the main channel has been greatly enhanced through erosion. Through the analysis on the measured hydrological data,the water and sediment regulation,the function of sediment-runoff regulation has been demonstrated.Under the non-saturation condition,the flooding discharse has created a strong effect of the erosion and deposition in the lower reaches of the Yellow River,increasing the discharge capacity,reducing the river bed elevation,and alleviating the trend by silting up year by year in downstream of Yellow River.

Ecological assessment of the yangtze river eco-system with benthic invertebrate as indicator species

Abstract: The aquatic ecology of the Yangtze River Basin was investigated and evaluated by using benthic invertebrate as indicator species.Investigation and sampling of water and benthic invertebrates were conducted from 2005～2007 at 36 selected sites on the upstream tributaries,middle and downstream reaches and riparian lakes of the Yangtze River.The water quality of the sites was evaluated with Hilsenhoff biotic index and compared with the results of chemistry analysis.The results show that the water in the most upstream tributaries are of high quality,water in the middle reaches of the Yangtze River and riparian lakes are slightly and moderately polluted;and the water quality in the lower reaches is even lower.The individual density,taxa richness and biodiversity of benthic invertebrate are high at the upstream sites,moderate in the riparian lakes of middle reaches,and low at the sampling sites in the middle and downstream reaches.Fluvial process condition has a significant effect on the benthic assemblage structure.This paper concludes the pedigrees of the benthic fauna in four types of fluvial process conditions for the Yangtze River Basin.Stable streambed provides the best habitat for bio-community and has the highest biodiversity.The bio-community is stressed in incised channels and the biodiversity is lower.In the stream experiencing siltation the habitat is seriously impaired and the biodiversity is even lower.In the stream with strong bed load movement there is no benthic macroinvertebrate.

Three-year sediment transport in a highly erodible catchment: The River Isabena (Ebro Basin, Southern Pyrenees)

Abstract: Quantifying suspended sediment load is important in catchments containing highly erodible materials, especially in those that drain into reservoirs since high suspended yields generates and exacerbates reservoirs siltation. Suspended sediment records are also essential for the calibration and validation of numerical models that aim to reproduce past soil erosion and sediment dynamics and to generate reliable data for management purposes. The River Isabena is a mesoscale (445 km) mountainous catchment located in the Southern Central Pyrenees in the Iberian Peninsula. The river experiences frequent floods, a characteristic that, together with the high connectivity between its network and the sediment sources, keeps sediment transport rates relatively high; instantaneous suspended sediment concentration occasionally attains 300 g l−1. The main sources of fine sediment are badland areas on marls (occupying less than 1% of the catchment area). The river flows into the Barasona Reservoir that experiences historical siltation problems.

Review on the study of sediment problems on the silt-sandy coast

Abstract: This paper makes summaries and comments on the studies of the definition of silt-sandy coast and its characteristics and genesis,the studies of silty sand movement patterns,basic features and laws,the studies of navigation channel siltation and layout of port and navigation channel,and the studies of scour around structures.It may play a role in guiding and promoting the further study in this issue.

Regulation and effect on siltation in outer channel of Huanghua harbor

Abstract: The sudden siltation in outer channel is mainly hindered the development of Huanghua harbor.Based on the analysis of survey data,dynamic condition,silt environment and siltation mechanism,the research method of silt and the actual effect on siltation after regulation project of Huanghua harbor were introduced.Combined with research work for several years on silt of Huanghua harbor,the research experience and learning including the seacoast division,the sudden siltation condition in the outer channel on silty coast,the movement form of silt,the characteristics of silty coast research and the regulation of sudden siltation in outer channel on silty coast were also introduced.

Sediment transportation of mud-dumping ground and effect on seaway siltation of huanghua port

Abstract: Particle tracking,neutron activation tracer sediment technique and formulas of Zhao and Yalin have been used to conduct research on sediment transport in mud-dumping grounds of Huanghua port.Furthermore,through these studies,effect on seaway siltation is analyzed.Results show that the sediment transport is dominated by tidal current under normal weather;nevertheless,under the condition of strong winds,wind wave,tidal current and wind-driven current play important roles in the sediment transport.Sediments from the mud-dumping grounds almost have no direct effect on seaway siltation under a single strong wind.The effect on seaway siltation from the mud-dumping grounds is indirect and limited.