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Tracing the origin of sediment is needed to improve our knowledge of hydro-sedimentary dynamics at the catchment scale. Several fingerprinting approaches have been developed to provide this crucial information. In particular, spectroscopy provides a rapid, inexpensive and non-destructive alternative technique to the conventional analysis of the geochemical properties. Here, we investigated the performance of four multi-proxy approaches based on (1) colour parameters, (2) geochemical properties, (3) colour parameters coupled with geochemical properties and (4) the entire visible spectrum to discriminate sediment source contributions in a mining catchment of New Caledonia. This French archipelago located in the south-west Pacific Ocean is the world's sixth largest producer of nickel. Open-cast nickel mining increases soil degradation and the downstream transfer of sediments in river systems, leading to the river system siltation. The sediment sources considered in the current research were therefore sediment eroded from mining sub-catchments and non-mining sub-catchments. To this end, sediment deposited during two cyclonic events (i.e. 2015 and 2017) was collected following a tributary design approach in one of the first areas exploited for nickel mining on the archipelago, the Thio River catchment (397 km2). Source (n=24) and river sediment (n=19) samples were analysed by X-ray fluorescence and spectroscopy in the visible spectra (i.e. 365–735 nm). The results demonstrated that the individual sediment tracing methods based on spectroscopy measurements (i.e. (1) and (4)) were not able to discriminate sources. In contrast, the geochemical approach (2) did discriminate sources, with 83.1 % of variance in sources explained. However, it is the inclusion of colour properties in addition to geochemical parameters (3) which provides the strongest discrimination between sources, with 92.6 % of source variance explained. For each of these approaches ((2) and (3)), the associated fingerprinting properties were used in an optimized mixing model. The predictive performance of the models was validated through tests with artificial mixture samples, i.e. where the proportions of the sources were known beforehand. Although with a slightly lower discrimination potential, the “geochemistry” model (2) provided similar predictions of sediment contributions to those obtained with the coupled “colour + geochemistry” model (3). Indeed, the geochemistry model (2) showed that mining tributary contributions dominated the sediments inputs, with a mean contribution of 68 ± 25 % for the 2015 flood event, whereas the colour + geochemistry model (3) estimated that the mining tributaries contributed 65 ± 27 %. In a similar way, the contributions of mining tributaries were evaluated to 83 ± 8 % by the geochemistry model (2) versus 88 ± 8 % by the colour + geochemistry model (3) for the 2017 flood event. Therefore, the use of these approaches based on geochemical properties only (2) or of those coupled to colour parameters (3) was shown to improve source discrimination and to reduce uncertainties associated with sediment source apportionment. These techniques could be extended to other mining catchments of New Caledonia but also to other similar nickel mining areas around the world.

The excess sediment load in canals generally causes the silting problem. The vortex chamber type silt excluders are used to extract the excess sediments from the canals to increase its discharge carrying capacity. The silt removing efficiency of silt excluder is generally calculated using the available empirical equations. The prediction results of the existing empirical equations were not found satisfactory. To improve the prediction results, a new model was developed using the artificial neural network (ANN). The experimental data were trained to developed the ANN model. The performance of developed ANN model was evaluated using two different statistical parameters MSE and R. These performance parameters suggest that the accuracy of developed ANN model improved significantly than that of other available empirical equations. The R value was found to be equal to 0.9863 which is quite closer to 1. In addition to this, the removal efficiency predicted using the ANN model lies within the error band of ± 20% which is more accurate than that predicted by existing empirical relationships in which the estimated removal efficiency lies within the error band on ± 40%.

The evolution of the Changjiang Delta is obviously affected by current rapidly rising sea level and drastically declining river discharge, and it is also vital for the sustainable development of Shanghai and the Changjiang River Economic Belt, which represent China’s economic development leader and major national strategic area, respectively. In this paper, the growth pattern of Jiuduansha Island, the largest uninhabited alluvial island in the Changjiang Estuary, is studied in terms of the change in elevation, position and area over the past 50 years through using satellite-derived instantaneous shoreline positions and high/low tide exposure areas based on 497 satellite images from 1974 to 2020; and the influencing factors and future development patterns are further discussed by comparison with other alluvial islands or sandbars in the estuary The results show that Jiuduansha Island has maintained a rapid or even accelerated area growth rate, although the sediment discharge of the Changjiang River has sharply decreased in recent decades This sustained growth is mainly attributed to the existence of the estuarine turbidity maximum zone, coarsening fluvial sediment, onshore sediment replenishment by tide, cone-like geomorphology of Jiuduansha Island, and siltation promotion effect of vegetation The growth rate of the low tide exposure area of Jiuduansha Island increased from 1.9 km2 a−1 in 1974–1990 to 3.0 km2 a−1 in 1990–2020, and the growth rate of the high tide exposure area reached as high as 3.7 km2 a−1 in 1994–2020. The implementation of the Deep-Water Channel Project has significantly affected the evolution of Jiuduansha Island, including shifting the heads of Shangsha and Zhongxiasha from severe retreat to rapid accretion, and promoting tidal flat progradation seaward of the Jiangyanansha and Zhongxiasha, but restricting the growth of the low tide exposure area of Jiuduansha Island.

Sagara Anakan Lagoon has been continuously receded caused by the high sedimentation rate. The deposited sediment volume was predicted to be around 1 million m 3 /year. This phenomenon, if not treated will harm the existing ecosystem and also could cause many kind s of its native biota extinct. Engineering could be applied to prevent it. However, the transport and sedimentation pattern must be known for it to be effective. Silting in Sagara Anakan Lagoon simulated by using MIKE21 numerical model which could simulate sediment transport in 2D horizontal scheme . The deposited sediment, mainly consisted of mud, so the model must be capable for simulating cohesive sediment transport. Model is set to simulate one year of morphological event which reached with the usage of time speed up acceleration factor. Model calibrated to be able to simulate a deposition event in the order of one million m 3 /year . M odel calibrated by tuning critical bed shear stress for deposition and erosion parameters as a base for sensitivity analysis . Model result shown that the sedimentation in Sagara Anakan Lagoon is caused by asymmetry of flood and ebb current. Major siltation happened around the delta with the maximum and mean observed bed change are approximately 0.6 m and 0.16 m respectively. The setup for this model could be used as a base model for planning an engineering approach for controlling sediment in Sagara Anakan Lagoon. Keywords : Numerical model, cohesive sediment, mud transport, estuary modelling Kata Kunci : Model numerik, sedimen kohesif, transpor lumpur, pemodelan estuari

Reservoir lotic–lentic transition regions typically show significant spatial and temporal hydro-sedimentological variability, highly influenced by their geometry. Previous assessment of the geometrical dependence of reservoir siltation overlooked potential impacts of internal structural alteration of such regions on their sediment trapping efficiency (STE). This study tested a hypothesis that partial confinement of such regions—a relatively inexpensive intervention—can generally increase their STE, thus contributing to sediment management with enhanced siltation control. Three-dimensional computational modelling of hydrodynamics and transport and deposition of suspended cohesive sediments was used to estimate STE for an idealised lotic–lentic transition region with subtropical characteristics under no-confinement and two types of partial confinement. A well-known and tested model was used with a thoroughly verified, mesh independent, numerically stable and mass conserving scenario modelling approach. Over 50 physically sound steady-state scenarios reproduced ranges of hydro-sedimentological and environmental conditions. Wind drove large-scale horizontal and vertical recirculating flow structures with which partial confinement interfered causing hydrodynamic discontinuity between ensuing upstream and downstream portions of the transition region. The study hypothesis was confirmed under such flow-pattern interference, as partial confinement increased STE by up to 16% relatively to corresponding unconfined setups. Transient conditions and other types of transition regions in real reservoirs need further investigation, but this finding is generally in-line with ‘pre-reservoir’ effects and had not been shown before. Such enhanced localised settling within lotic–lentic transition regions caused by partial confinement can provide additional control over reservoir siltation when considered in combination with other sediment management alternatives.

Instream hydraulics and riverbed substrate allow for the identification of mesohabitats, and contribute in shaping benthic macroinvertebrate assemblages. However, the role of different depositional conditions between mesohabitats in determining macroinvertebrate response to large sediment input still needs investigation. We studied the evolution of sediment deposits and benthic assemblages in two mesohabitats (a riffle and a glide) of an Alpine river affected by an extreme sediment input. Substrate and hydraulic characteristics were measured in each mesohabitat for 18 months after the sedimentation event. Benthic macroinvertebrates were sampled concurrently, and available pre-event data allowed for before/after comparison. We found evidence of a different response of benthic communities to siltation, associated to the physical structure of the mesohabitat they inhabit. Both substrate and macroinvertebrates were less impacted and recovered faster in the riffle than in the glide. Assemblages in the glide adjusted to the modified habitat through strong proliferation of sand tolerant and preferring families, resulting in higher density and lower diversity compared to the riffle. Our results could support the improvement of the impact assessment of sediment input events. This is particularly relevant given the current global warming, inducing the increase in frequency and intensity of severe rainfall events, and subsequent landslides.

Erosion of geological units and sediment load in rivers can be considered as the serious problems in recent decades. Increasing sediment loads generate major hazards for water resources development, particularly in terms of loss of reservoir storage due to sedimentation and siltation of water distribution systems. In this paper, the performance of four sediment rating curve (SRC) development methods was evaluated for the Shirin Darreh River (SDR) basin (1750 km2), located in North Khorasan Province, Iran. Data of flow discharge (Q) and suspended sediment flux (SSF) (Q-SSF pairs, N=957) and daily flow discharge, recorded by the Regional Water Company of North Khorasan (RWCNK) at the Qaleh-Barbar (QB) gauging site during 1989–2018 were used. The flow discharge classification method performed best by meeting the desired criteria of most statistical indices, including normalized root mean square error (NRMSE), mean bias error (MBE), mean absolute error (MAE), index of agreement (d), and coefficient of determination (R2). Based on the optimized method, the rate of suspended sediment transportation at the study site was estimated about 2.7×106 ton year−1. Erodibility of the exposed formations in the study area was estimated based on a factorial scoring model (FSM). Three indices, focused on the outcrop and erodibility, were calculated for the geological units at sub-basin and total scales. Marl deposits are the most extensive geological unit in the three sub-basins and the maximum formation outcrop ratio (FOR) and participation in erosion (PCE) were obtained for these rocks at total scale. In fact, marl unit can be regarded as the main source to supply the suspended sediments in the study basin.

Waduk Jatiluhur merupakan salah satu waduk serbaguna di Jawa Barat dengan peruntukkan Pembangkit Listrik Tenaga Air (PLTA), penyediaan bahan baku air minum (PDAM) dan industri, penyediaan air irigasi, perikanan, pariwisata dan pengendalian banjir. Berdasarkan laporan akhir Perum Juanda pada tahun 2000 bahwa volume waduk pada tahun 1964 adalah 2,970 juta m³, pada tahun 1987 adalah 2,556 juta m³, tahun 1995 adalah 2,456 juta m³ dan pada tahun 2000 adalah 2,448 juta m³. Hal ini menunjukkan bahwa volume waduk telah berkurang sebanyak 522 juta m³ dalam kurun waktu 36 tahun pada ketinggian ± 107 mdpl. Tujuan penelitian ini adalah untuk menghitung sedimentasi di Waduk Jatiluhur pada tahun 2018. Pengukuran TSS menggunakan SNI 06-6989.3-2004 dan perhitungan sedimentasi menggunakan metode pengukuran langsung. Hasil penelitian menunjukkan bahwa total sedimen di inlet waduk adalah 859,368.40 ton tahun-1 dan outlet waduk adalah 92,553.33 ton tahun-1. Berdasarkan data tersebut maka total sedimen yang mengendap di Waduk Jatiluhur pada tahun 2018 adalah 766,815.07 ton. Sehingga diperlukan penanganan dalam mengurangi sedimen agar waduk tidak mengalami pendangkalan.

This study aimed to analyze the pattern of sediment transport to the distribution of plankton and fishing ground in the estuary of KamparRiver. This study used survey methods, the study sample was obtained in the field are considered to represent the Kampar River estuary. Then the sampling results in the form of TSS, brightness, temperature, salinity, pH, flow velocity and plankton descriptively analyzed and discussed with reference to data interpretation method by using mathematical models (software mike21 ). The results showed the concentration distribution of sediment at the mouth of the Kampar River in east monsoon amounted to 8.76 million tons / day and in the west monsoon amounted to 7.64 million tons / day. A region prone to silting due to sediment transport is periodically southeastern portion Mendol. Based on the analysis modeling , plankton diversity index tends to be low in the study site so that the waters around the Mendol island excluding strategic area for fishing grounds it is indicated there has been a downward trend in plankton diversity index as the primary productivity . The existence of TSS may hinder the penetration of light that ultimately affect the photosynthetic plankton.

Hydropower generation is one of the key purposes that dams were built for. World-wide the sustainability of hydropower operation is deprived and threatened by the alarming rate of reservoir sedimentation. The situation is even worst for the cases where the sediment delta has propagated and reached the dam site. Various sediment management practices have been employed to cope with the problem at a huge amount of cost. This paper analyses the sedimentation problem and the impact on hydropower generation in Roseires reservoir, in Sudan. An economical reservoir sediment management plan such as Hydro-suction dredging technique is suggested. The deposited sediment should be agitated before being bypassed to the downstream via a pipeline that makes use of the natural hydraulic head of water. A detailed design procedure is outlined and guidelines for the optimization are presented. The procedure is theoretically illustrated by applying it to remove the annual deposited sediment ahead of Roseires Hydropower intakes in Sudan. It was concluded that such system is cost effective when compared to costs incurred in tackling the effect of siltation in front of hydropower intakes.

Water resources in Moulouya basin situated in the North East of Morocco depends on Mohammed V and Mechraa Hammadi dams which are old and very impacted by siltation. To water supply of Oujda city and surroundings little towns a new water intake was implemented in Mechraa Hammadi dam reservoir. The better site for the intake location and a syphon type were chosen to ovoid sediment problems generated by the resuspension of particles. Thus, two-dimensional and Horizontal numerical model was developed to analyze the silting of dam especially near the intake location. The objective of this research is to examine sediment conditions surrounding a water intake and their possible repercussions on its operation and their probable impacts on water drinking supply. Numerical modeling analysis allowed to study the water supply intake operation and the risks of production shut-down. Three extreme scenarios were considered to predict the probable shortages and their range of variation. The final results of different simulations for predicting periods of shutdown of drinking water production for each scenario, considering the concentration rate of suspended sediments generated by extreme floods, were presented. Taking into account the plant capacity treatment of sediment turbidity fixed to 30 g/l, the probable duration of shutdown of the drinking water varies between one day and a maximum period of 3 days.

Erosion and sedimentation caused 4,000-hectare siltation in Limboto. Experts predicted that Limboto will be extinct in 2031. Revitalization program ‘Limboto Lake Revitalization’ has been carried out since 2017, with sabo technology as the action carried out to restrain sedimentation rate and to save the lake from extinction. This study aims to measure erosion and sedimentation potential in upstream of Limboto including 12 rivers (sub-DAS), using WaTEM/SEDEM model Two outputs resulted through this study are total sedimentation potential and identification of sedimentation zoning on each river. Based on soil type and other triggering factors, 5 of 20 rivers have the biggest sedimentation potential to deliver to Limboto, namely Batulayar 193.662 m3, Biyonga Baluta 123.095 m3, Alo1 120.273 m3, Alo 115.204 m3 and Molamahu 73.058 m3. The model was visually calibrated by considering the rivers’ sedimentation volume collected by JICA and BWS Sulawesi II. The result shows different score depending on the soil type, slope, land cover and other parameters. Sabo dam has to be reviewed regularly and on-schedule, since its current data is not actual and upstream rivers have highly dynamic and fluctuative sediment as well.

This specific study was conducted on the Abrajit reservoir in east Gojjam, Amhara region, Ethiopia. The general objective of the study was to investigate reservoir siltation and determination of the remaining valuable life span of the reservoir using ArcGIS 10.5 version and Golden surfer 16 latest version. A bathymetric survey using echo-sounding equipment (Garmin GPSMAP421s) was conducted and a topo map of reservoir data was used for assessment of the sediment volume. The accumulated sediment volume was estimated by subtracting the triangular interconnected network (TIN) map of the initial bed level from the currently measured bed level. The result of the research revealed that to date, 343,700.1 m3 bulk of sediment was accumulated in the reservoir that reduces 20% of the total reservoir capacity. In the results from the bathymetric investigation and software analysis, annually 28,641.675 m3 year−1 amount of sediment is coming from the catchments to the reservoir that contributed 1.66% of annual reservoir volume reduction. The measured recent storing capacity for the Abrajit Dam was 1,388,870 m3. From a comparison of remaining reservoir storage and annual sediment load, the reservoir will not serve more than 12 years. The estimated specific sediment yield (SSy) was found to be 4733.387 ton km−2 year−1. Therefore, to improve the estimated life span of the reservoir, watershed management is very important and further study is required to identify the area where watershed conservation will focus in the future. Upon the findings, the reservoir volume is running to reduce and it cannot serve all the demand what it designed for during the dry season. As a result, operation curves should be mandatory to give water service for the critical water needs, and regular monitoring of sediment accumulation in the reservoir is recommended.

Bendung Kumala dibangun di Sungai Krueng Baro yang merupakan salah satu sungai strategis di Provinsi Aceh untuk mengairi lahan irigasi dan air minum bagi masyarakat di hilirnya, namun sungai ini memiliki permasalahan yang cukup besar sehubungan dengan jalurnya yang panjang dan melewati berbagai formasi geologis. Kondisi ini menyebabkan konsentrasi sedimen yang tinggi pada sungai. Oleh karena itu, penelitian ini bertujuan untuk menganalisisis hidrodinamika sungai dengan menggunakan aplikasi HEC-RAS 5.0. Hasil penelitian memberikan informasi bahwa kapasitas aliran sedimen transport sepanjang dasar sungai bervariasi secara langsung dengan adanya perbedaan antara tegangan geser pada sedimen dasar dan tegangan geser kritis yang diizinkan untuk partikel yang bergerak. Semua sampel sedimen pada hulu dan hilir Bendung Keumala terjadi angkutan sedimen. Pengurangan aliran akibat adanya pembendungan menyebabkan perubahan pada saluran dan rezim alirannya, dan pengurangan pelepasan air telah menyebabkan terjadinya pengurangan angkutan sedimen melayang dan sedimen dasar ke arah hilir. Total sedimen yang terdapat di sekitar areal bendung pada saat debit normal sebesar 6.325.698,93 ton/tahun. Sedimentasi di sekitar bendung menjadi masalah yang serius karena dapat mempengaruhi fungsi dan kinerja bendung dan saluran irigasi. Selain itu pendangkalan akibat sedimentasi menyebabkan tertutupnya intake PDAM Keumala. Untuk mengatasi masalah ini, perlu dilakukan pengerukan dan pengangkutan sedimen dari dasar bendung secara berkala. Pengerukan dan pengangkutan sedimen akan meningkatkan kinerja Bendung Keumala untuk mengairi Daerah Irigasi Krueng Baro. Kapasitas pengaliran intake bendung dapat tetap terjaga untuk mengairi lahan irigasi sesuai dengan areal rencana.

Reservoirs are an important source of water supply, provide hydropower, reduce the deficiency influences, and provide flood protection. Due to the dam structure and reservoir founding, the releases from the dam has become more restrained and the hanging sediment concentricity summits have been decreased considerably and accumulated upstream the dam. Sediment siltation has increasingly reduced the efficiency of reservoir functionality throughout the years by declining the storage capability. Determining the reservoir sedimentation influence on the dam operation is important to holding current operation and preparing for future polices. The existing paper deals with the review and assessment of the reservoir sedimentation effect on operation of Aswan High Dam (AHD) in Egypt. A new simulation model was developed and calibrated for Aswan High Dam Reservoir (AHDR) to evaluate the reservoir sedimentation effects on the factors affecting the operation of the dam. These factors are Toshka spillway outflows, upstream water levels of AHD, dam safety, withdraw from the reservoir, the losses due to the evaporation and the hydropower generation from AHD. The results of the study displayed that the factors affecting the operation of AHD were affected due to presence of these deposits in AHDR. Therefore, the reservoir sedimentation effect should be considered to implement or develop of simulation models for AHDR.

Scour is a natural phenomenon involving the removal of bed sediments by the perturbation of flow field with the erection of hydraulic structures such as guide bank, abutments and bridge piers. Remo...

L'erosion et le transport solide sont des problemes serieux a l'echelle mondiale mais ils sont bien plus preoccupants dans certaines regions du monde, comme c'est le cas au Maghreb et plus particul...

Since the period of human civilization, the hydrological and morphological characteristics of most of the rivers have been intensively modified by human interferences. In this context, the Ichamati River is one of the worst affected distributary channels flowing on the lower Gangetic delta of South Bengal. This tidally active river is streaming on the most densely inhabited district (North 24 Parganas) of West Bengal. The river is gradually decaying over time due to direct and indirect human activities on and along the river. Therefore, the prime aim of this research study is to explain the temporal change of the channel behaviour, especially fluvio-morphological characteristics of the river during 1976–2016. The present study also highlights location-specific causal factors liable for the downstream modification of the channel behaviour. In this research study, channel migration, erosion rate, bank vulnerability zone and channel planform pattern have been assessed using Landsat images of 1976, 1996 and 2016 in remote sensing and GIS environment. Besides, an intensive field survey was conducted for cross-sectional survey of the river. Primary data were gathered from brick kilns through a questionnaire survey for the estimation of sediment extraction rate from the river to prepare the sediment-water budget of the river. This study reveals that the morphological characteristics of Ichamati River have been modified at the human–nature interface and continuous siltation causes gradual upliftment of the riverbed. The channel is gradually narrowing and decaying over time. This study is helpful to understand the current status of the river and helps river scientists for its restoration as well as management planning.

In order to clarify the distribution and variation of silt and fluid mud in the Waiganmen shallow section of the 50000-ton intake channel of the Xiangshan Port, and to understand the influence of the channel excavation on the surrounding flow conditions and the strength of the backsilting, especially the impact of typhoon on the sudden silting of the channel, so as to demonstrate the feasibility and stability of the channel excavation. The fluid mud, hydraulic, sediment and topographic measurements were carried out in the study area, and the thickness of the fluid mud layers, tidal current, sediment and topographic data were obtained. Dual-frequency sounder, gamma-ray densitometer and SILAS navigational fluid mud measurement system were used to monitor the fluid mud, and the results were compared and verified. The adaptability and accuracy of the three methods were analyzed. The SILAS navigational continuous density measurement system and gamma-ray fixed-point fluid mud measurement are used to detect the density, thickness and variation of the fluid mud accurately. Based on the hydrological observation data, the process of erosion and deposition in excavation channel and its influence mechanism are analyzed, and the distribution characteristics and evolution law of siltation in engineering area are given in the form of empirical formula. The research shows that the super typhoon can produce large siltation, which results in sudden siltation of the channel. The tidal current is the main dynamic factor of the change of erosion and siltation of the excavation trench. Under the influence of reciprocating tidal current and excavation topography, the trial excavation trench is silted on the whole. There is fluid mud in the monitoring area of the trench, and the distribution of fluid mud is different in space. The thickness of the fluid mud at the bottom of the trench is generally larger than that outside the trench and the slope of the trench, and the siltation of the trench tends to be slow. The research results can provide scientific evaluation for channel excavation and maintenance, and support for the implementation of the project.

Worldwide, stream water is increasingly loaded with sediments and nutrients, due to processes such as accelerated soil erosion and overfertilization caused by agricultural intensification. This leads to increases in eutrophication and silting up of bottom sediments. Floodplains can play an important role in mitigating these problems, by removing sediment from rivers via water filtration and retention. Fine sediment is accumulated on the soil in between plants as well as on plant surfaces. However, it is still poorly understood how plant species facilitate leaf surface sedimentation via their leaf traits. In a flume experiment, we investigated to what extent the leaf traits (area, length, perimeter, pinnation, pubescence, surface roughness, flexibility and wettability) influence leaf surface sedimentation. We exposed leaves of 30 plant species to an artificial flood, and measured the fine sediment load the leaves captured after 24 h. Our results show that leaf traits overall explain 65% of the variation of fine sedimentation on leaves. Especially adaxial pubescence and leaf area strongly drove sedimentation. Hairy leaves accumulate more sediment per leaf area, presumably, because hairs create a buffer zone of reduced flow velocity which enhances sedimentation between the hairs. Additionally, for leaves with no or few hairs, sedimentation decreased with increasing leaf area, because most likely the more turbulent boundary layer of larger leaves allows less sediment to settle. Our results provide a first understanding of how plants can be selected based on their leaf traits for maximizing the sediment retention on floodplains, thereby providing a key ecosystem service. Electronic supplementary material The online version of this article (10.1007/s00442-020-04664-2) contains supplementary material, which is available to authorized users.

The Southern California Bight is adjacent to one of the world's largest urban areas, Los Angeles. As a consequence, anthropogenic impacts could disrupt local marine ecosystems due to municipal and industrial waste discharge, pollution, flood control measures, and global warming. Santa Monica Basin (SMB), due to its unique setting in a low-oxygen and high-sedimentation environment, can provide an excellent sedimentary paleorecord of these anthropogenic changes. This study examined 10 sediment cores, collected from different parts of the SMB between spring and summer 2016, and compared them to existing cores in order to document changes in sedimentary dynamics during the last 250 years, with an emphasis on the last 40 years. The 210Pb-based mass accumulation rates (MARs) for the deepest and lowest oxygen-containing parts of the SMB basin (900–910 m) have been remarkably consistent during the past century, averaging 17.1±0.6 mg cm−2 yr−1. At slightly shallower sites (870–900 m), accumulation rates showed more variation but yield the same accumulation rate, 17.9±1.9 mg cm−2 yr−1. Excess 210Pb sedimentation rates were consistent with rates established using bomb test 137Cs profiles. We also examined 14C profiles from two cores collected in the deepest part of the SMB, where fine laminations are present up to about 450 yr BP. These data indicate that the MAR was slower prior to ∼1900 CE (rates obtained were 9 and 12 mg cm−2 yr−1). The δ13Corg profiles show a relatively constant value where laminations are present, suggesting that the change in sediment accumulation rate is not accompanied by a change in organic carbon sources to the basin. The increase in sedimentation rate towards the Recent occurs at about the time previous studies predicted an increase in siltation and the demise of a shelly shelf benthic fauna on the SMB shelf. X-radiographs show finely laminated sediments in the deepest part of the basin only, with centimeter-scale layering of sediments or no layering whatsoever in shallower parts of the SMB basin. The absence of finely laminated sediments in cores MUC 10 (893 m) and MUC 3 (777 m) suggests that the rate at which anoxia is spreading has not increased appreciably since cores were last analyzed in the 1980s. Based on core top data collected during the past half century, sedimentary dynamics within SMB have changed minimally during the last 40 years. Specifically, mass accumulation rates, laminated sediment fabric, extent of bioturbation and % Corg have not changed. The only parameter that appeared to have changed in the last 450 years was the MAR, with an apparent > 50 % increase occurring between ∼1850 CE and the early 1900s. The post-1900 CE constancy of sedimentation through a period of massive urbanization in Los Angeles is surprising.

Erosion and solid transport is a tricky and complex problem that negatively affects natural and urban environments. In Algeria, the effects of this phenomenon are apparent; their impact is no less devastating in the long term than the other spectacular catastrophic phenomena that can be observed. Sixty-five large dams in Algeria are threatened by the reduction of 62% of their storage capacity because of the siltation problem (ANBT) (National Agency for Dams and Water Transfers). The main objective of this work is the evaluation of the impact of the erosion phenomenon on Bechar watershed which is in an area characterized by an arid climate. The universal soil loss equation was used. This model is based on the combination of the five factors (erosivity, erodibility, topography, vegetation cover and support practices) that directly influence this phenomenon. Analytical hierarchy process is used to give a weighting value of each factor according to its degree of influence on the phenomenon. The sediment delivery ratio is calculated to determine the amount of soil that will arrive at the outlet of the watershed and contribute to the storage structures siltation. The obtained results will undoubtedly help decision makers to understand the threat of erosion degree in the study area in order to better take the necessary measures to face this issue.

The morphological evolution characteristics of the North—South Passage area since the construction of the Yangtze Estuary Deepwater Navigation Channel Project (DNCP) are analyzed on the basis of the measured data. A two-dimensional morphodynamics numerical model of the Yangtze Estuary is established to verify the morphological evolution of the North—South Passage under the influence of the DNCP and to predict the future evolution in the next 40 years. Data analysis shows that the North Passage has experienced rapid adjustment stages and adaptive stages after the construction of the DNCP. Slow erosion occurred along the main channel, and slow siltation could be observed in the area between the groins. The South Passage showed a state of upper section erosion and down section deposition. At present, the whole South Passage is in a slight erosion state. According to the numerical model, the eroding and silting speed of the North Passage will slow down in the future. The present state that erosion occurs in the main channel and siltation occurs between the groins will continue. The South Passage will still maintain upper section erosion and down section deposition in the future. Due to the main channel erosion of the North Passage and siltation of the South Passage, the sediment division ratio of the North Passage will increase in the future but still be smaller than 50%. After morphological evolution of 40 years, the direction of residual sediment transport caused by M2 and M4 tidal components in the North Passage has not changed, but the transport rate will decrease. It is considered that the morphological evolution of the North—South Passage could reach a relatively stable state after 40 years.

The Fukushima Daiichi nuclear power plant accident caused radioactive pollution in northeastern Honshu Island, Japan. This study examined the influence of snowmelt and rainfall on soil erosion processes and siltation of small lakes in Miyagi Prefecture (150 km northwest of the power plant). Two sets of slopes and lakes, respectively in pasture and forest catchments, were examined. Snowpack thickness, soil infiltration, surface runoff volume, soil and sediment physicochemical properties, Cs concentration of precipitation, meltwater, and rainwater, and lake siltation rates were determined. The total radioactive Cs content in precipitation was 0.7–7.4 BqˑL−1 and was below the Japanese standard (10 BqˑL−1). Total radioactive Cs was at the allowable level in water flowing down the pasture catchment slope (0.1–9.2 BqˑL−1) during snowmelt and rainfall, as well as in pasture (0.9–8.8 BqˑL−1) and forest (0.7–5.2 BqˑL−1) catchment lake water. There was no soil erosion (surface runoff) in the forest catchment. Soil losses in the pasture catchment were 23 due to rainfall and 9 kg ha−1 yr−1 following spring snowmelt. After snowmelt, a 0.5 and 0.2 mm thick layer of silt was deposited in pasture and forest catchment lakes, respectively, and 1.4 and 0.6 mm were deposited during the rainfall period. Average siltation rates were 1.9 and 0.8 mmˑyr−1 for pasture and forest catchment lakes, respectively. The upper layer of lake bottom sediments is represented mainly by silt fractions (2–50 μm), with high organic matter (4.0–5.7%) and radiocesium (1100–1600 kgˑha−1) contents. Keywords: Fukushima Daiichi, Radiocesium, Siltation, Suspended sediment, Waterbodies, Water turbidity

Based on the measured discharge, sediment load, and cross-sectional data from 1986 to 2015 for the lower Yellow River, changes in the morphological parameters (width, depth, and cross-sectional geomorphic coefficient) of the main channel are analyzed in this paper. The results show that before the operation of the Xiaolangdi Reservoir (XLDR) from 1986 to 1999, the main channel shrunk continually, with decreasing width and depth. The rate of reduction in its width decreased along the river whereas that of depth increased in the downstream direction. Because the rate of decrease in the width of the main channel was greater than that in channel depth, the cross-sectional geomorphic coefficient decreased in the sub-reach above Gaocun. By contrast, for the sub-reach below Gaocun, the rate of decrease in channel width was smaller than that in channel depth, and the cross-sectional geomorphic coefficient increased. Once the XLDR had begun operation, the main channel eroded continually, and both its width and depth increased from 2000 to 2015. The rate of increase in channel width decreased in the longitudinal direction, and the depth of the main channel in all sub-reaches increased by more than 2 m. Because the rate of increase in the depth of the main channel was clearly larger than that of its width, the cross-sectional geomorphic coefficient decreased in all sub-reaches. The cross-sectional geometry of the main-channel of the lower Yellow River exhibited different adjustment patterns before and after the XLDR began operation. Before its operation, the main channel mainly narrowed in the transverse direction and silted in the vertical direction in the sub-reach above Aishan; in the sub-reach below Aishan, it primarily silted in the vertical direction. After the XLDR began operation, the main channel adjusted by widening in the transverse direction and deepening in the vertical direction in the sub-reach above Aishan; in the sub-reach below it, the main channel adjusted mainly by deepening in the vertical direction. Compared with the rates of decrease in the width and depth of the main channel during the siltation period, the rate of increase in channel width during the scouring period was clearly smaller while the rate of increase in channel depth was larger. After continual siltation and scouring from 1986 to 2015, the cross-sectional geometry of the main-channel changed from wide and shallow to relatively narrow and deep. The pattern of adjustment in the main channel was closely related to the water and sediment conditions. For the braided reach, the cross-sectional geomorphic coefficient was negatively correlated with discharge and positively correlated with suspended sediment concentration (SSC) during the siltation period. By contrast, the cross-sectional geomorphic coefficient was positively correlated with discharge and negatively correlated with SSC during the scouring period. For the transitional and meandering reaches, the cross-sectional geomorphic coefficient was negatively correlated with discharge and positively correlated with SSC.

The St Lucia Estuary is the largest estuarine lake in Africa and has been heavily impacted by anthropogenic activities, which include a history of human-induced sediment loading and separation in t...

The paper aims to show the preliminary monitoring and field test results of the innovative technology tested in the framework of the MARINAPLAN PLUS LIFE project for sustainable management of sediment in harbour areas. The technology is based on a patented jet pump that will be able to keep the seabed at a certain level over the time through a continuous removal of silting sediments. Preliminary field tests were performed to optimise the design of the demo plant and a monitoring plan was devised to evaluate the technical, economic and environmental impacts of the technology, in particular in comparison with dredging. The preliminary tests showed promising results in terms of efficacy and efficiency of the sediment by-passing device. At the maximum sediment removal capacity, the ejector tested in Cervia showed a sediment flow rate of about 2 m3 h−1, with an electric consumption of about 3.5 kW, and an influence diameter of about 5–7 m, after 15 days of working operation. On the basis of the preliminary results, a 10-ejector demonstrator plant has been designed and realised, and it is now in operation. The analysis of sediment and marine flora and fauna in the installation area in comparison with control areas indicates the negative impact of cyclic dredging in the harbour inlet area. The innovative technology promoted by the MARINAPLAN PLUS LIFE project is a promising solution to manage sediment siltation in harbour areas through a cost-effective and low environmental impact technology. The monitoring of the demo plant operation is fundamental to fully validate the technology and to demonstrate its efficacy and sustainability.

The study involved qualitative and quantitative analysis of suspended sediment and its origin in a small reservoir located in Blizne, Podkarpackie Region (SE Poland), and was conducted during summer 2017. Results showed a linear negative correlation between the suspended sediment in a water column and its organic matter content. There was also a clear relationship between the suspended sediment content and the rate of sedimentation of solid particles suspended in the water column. The research showed that the TOC-to-OM conversion factor commonly applied to bottom sediments does not apply to sediments suspended in the water column. It was also observed that the organic matter prevailing in entrapped sediment was of autochthonous origin. Its share was greatest and the content of total phosphorus highest when retention period increased. The increase in phosphorus content co-occurred with the decreasing TOC:TN ratio, and with a decrease in the sedimentation rate. Analysis has thus shown that the composition and specific nature of suspended sediment in this reservoir affects the rate of deposition of matter and can determine the siltation processes.

Increasing continental suspended sediment influx to coral reefs is an example of land-sea coupling that requires the identification of sources, magnitude of transport, and controlling processes. In Brazil, a small coastal basin (Macae River) was identified as a source of suspended sediment to a coral reef on the coast of Cape Armacao dos Buzios. Biannual suspended sediment loads were measured at the basin as were fluxes within the estuary and towards the coast during eight tidal cycles. Particle load and yield from this basin were typical of small coastal basins, showing high to moderate slopes and transitional land management. However, the magnitude of the river loads was lower than the sediment transport within the estuary, indicating that the estuary amplifies river fluxes and sustains the transference of suspended sediment alongshore to the coral reef. Nonetheless, the estuary displays both suspended particle retention and export capacity and, therefore, fluxes to the coast and the coral reef occur as episodic events.

The geochemical composition of rare earth elements (REE) in the bottom sediments of two Dominican reservoirs and in soils from their catchments was studied to identify possible sources of the deposited materials. Knowledge of the origin of the sediments will serve to control the excessive rates of erosion and sedimentation that occur annually due to periodic extreme climatic events that promote excessive silting of the lakes, followed by loss of storage capacity and degradation of water quality. The REE contents of sediments and soils were normalized to the North American Shale Composite (NASC) and the ratio of light/heavy rare earths (LREE/HREE ratio), Ce and Eu anomalies, and some fractionation parameters were determined. The REE patterns are more homogeneous in the sediments, indicating uniform sedimentation in both deposits. The sediment data reflect depletion of REE from the sources, enrichment of light REE (LREE) and some middle REE (MREE), and positive Eu and Ce anomalies. All data were plotted in correlation diagrams between some fractionation parameters of light–middle–heavy REE and anomalies of Ce and Eu. The similarity of the ratios between these parameters in all samples and the overlap of data from soils and rocks on the sediment projection in the diagrams allowed a good discrimination of the main sources of the materials.

Lack of a systematic and environmentally efficient approach to exploitation of bays of Sevastopol (Kruglaya and Kazachya bays) resulted in their severe pollution. The combination of natural and anthropogenic factors led to the deterioration of the benthic communities living conditions. The purpose of this work was a complex research of Kruglaya and Kazachaya bays’ ecosystems to study features of redox conditions formation in the bottom sediments and the bottom waters and their influence on the characteristics of macrozoobenthos. Samples of bottom sediments were taken by diver in plexiglass tubes, hermetically closed above and below, it allowed to save a fine structure of bottom sediments and the bottom layer of water. To study benthic communities, samples were taken in the same place using a manual sampler. To obtain the chemical composition of pore waters with high vertical resolution, the voltammetry analysis was used. Calculation of the oxygen flux at the boundary and in the upper part of the bottom sediments was carried out according to the vertical profile of oxygen concentration in pore waters and geochemical analyzes using the equation for the first Fick law taking into account the concentration gradient and molecular diffusion of oxygen in pore waters. Standard hydrobiological methods were used for the analysis of benthic material. When calculating the values of the Shannon diversity index (H'), the base 2 logarithm was used. The data analysis showed that a high level of anthropogenic impact and restricted water dynamics led to siltation of the bottom sediments of the investigated water areas, which made it difficult for oxygen penetration, and the accumulation of organic carbon contributed to its active consumption. Stratification of the water column due to limited water exchange, high temperature of the bottom waters, accompanied by a decrease in oxygen solubility, and finely dispersed nature of bottom sediments contributed to the fact that the rate of oxygen intake was lower than the rate of oxygen consumption for the oxidation of organic matter, which was accompanied by the development of oxygen deficiency zones and the appearance of reduced compounds, in particular hydrogen sulfide. It was noted that suboxic conditions prevailed in the upper layer of bottom sediments, and anaerobic conditions prevailed below. This had led to the fact that the main forms of macrozoobenthos were species tolerant to oxygen deficiency and organic pollution. Thus, in some parts of the Kazachaya Bay were marked only polychaetes. At the same time, it was noted that in the area of exit from Kruglyaya Bay, intense water dynamics and morphological features of the bottom sediments contribute to saturation of the upper layer of sediments with oxygen. Based on the oxygen concentration data in the surface (0 - 5 mm) sediment layer (pore water), and the geochemical composition of bottom sediments, the oxygen flux at station 4 was calculated. Its value was 0.73 M·m-2·year-1. Taking into account the concentration of oxygen in the bottom layer of water (259 μM), the time for complete exhaustion of oxygen or its renewal taking into account only biogeochemical processes was about 5 months. Thus, it can be assumed that the ecosystems of the Kruglaya and Kazachaya bays are in the stage of degradation. Its further exploitation without a developed systematic approach and rational use will lead to a critical deterioration of its ecosystem - the emergence and spread of environmental risk zones. This will reduce the recreational and socio-economic attractiveness of these areas.

Fine sediment has a critical role in river ecosystems and is essential for habitat heterogeneity, ecosystem structure and function. Expansion and intensification of specific land uses, including agriculture, have increased fine sediment inputs into river networks. The detrimental impacts of excessive fine sediment on river ecosystems have been well documented and numerous sediment targets have been proposed or adopted to assess the gap between target and current levels of fine sediment. Where sediment targets exist, these are often over-simplified and applied across a wide range of river environments irrespective of the processes of fine sediment deposition and the tolerance or sensitivity of river biota to fine sediment. Thus, targets often fail to provide a reliable basis for identifying the need for management interventions to restore ecosystem health. This review adopts a system-based approach to the impacts of fine sediment after reviewing the suitability of existing targets for guiding management in chalk stream catchments specifically. Chalk streams are groundwater-dominated systems characterised by stable hydrological, ecological and thermal regimes and thus respond differently to excessive fine sediment compared with other fluvial systems. Chalk streams are often subject to high levels of sedimentation and siltation despite their low suspended sediment loads. In this paper, we review the characteristic processes and dynamics of chalk streams and how these influence fine sediment accumulation. The impacts of excessive fine sediment on chalk stream habitats and biota and the role ecosystem engineers play in the processes of fine sediment dynamics are discussed. Finally, we discuss the application of fine sediment targets for chalk streams in relation to the implementation of both source and process-based techniques for meeting the requirement for improved ecosystem management.

The domain of Chantilly (Oise, France) includes a castle and a garden, both dating from the eighteenth century, which are seen as important legacies of France’s history. Nowadays, the 2.5 km canal that runs through the domain is subject to the phenomenon of silting, leading to the accumulation of sediments within the canal linked to the proliferation of algae, which has a dissuasive effect among visitors. HEC-RAS software (Hydrologic Engineering Centers River Analysis System, US army corps of Engineers, Washington, D.C., USA) was used to model and understand sediment accumulation within the canal. This model is widely used in the literature tackling sediment transport and accumulation, and allows the forecasting of which stretches of the canal are most susceptible to sediment accumulation. The simulation results highlight an accumulation of sediment near the entrance of the Nonette stream into the canal and a propagation through the canal. The total accumulated volume assessed by the model between 2001 and 2010 equals 3901 m3, when the reconnaissance of the catchment showed the sediment was not a limiting factor. However, the volumes determined are underestimated, as matter brought by vegetation or other systems different from the river (e.g., wind, rainfall) is not considered in the calculation. The quantity of sediment is also subject to uncertainties, as the bathymetry of the canal is not available.

Even though wind, water depth, and shear stress are important factors governing sediment resuspension in lakes, their actual relations to total suspended solids (TSS) distribution in natural environments have not been well elucidated. This study aims to elucidate the impact of the wind on the spatio-temporal variation of TSS in Tonle Sap Lake, Cambodia, during low-water (March and June, &lt, 1 m) and high-water (September and December, 8–10 m) seasons. To this end, wind and TSS data for December 2016 and March, June, and September 2017 were collected and analyzed. For spatial interpolation of wind speed, the inverse distance weighted method was found to be better (R2 = 0.49) than the vectorized average (R2 = 0.30) and inverse of the ratio of distance (R2 = 0.31). Spatial interpolation showed that the wind speed and direction on the lake were &lt, 5 m/s and southward during the low-water season and &lt, 7 m/s and westward during the high-water season. The TSS concentration in the low-water season was higher (&gt, 50 mg/L) than that in the high-water season. The TSS concentration during the low-water season was empirically described by wind speed (W), water depth (D), and shear stress (τ_wave) with a function of W3, W3/D, and exp(W/D) or exp(τ_wave), depending on the location in the lake. The critical shear stress due to wind-induced waves at most of the places in the lake was higher than the total shear stress indicated. Sedimentation was predominant in December and June, and erosion (siltation) was dominant in March. Most of the siltation in March was dominant in the southern part of the lake.

The effectiveness of the use of accumulation basins ordinarily used for river sediment to reduce the rate of silting of the reservoirs of hydroelectric power plants situated on mountain rivers is considered. The investigation is performed by methods of numerical hydrodynamic simulation based on the two-dimensional Saint-Venant equations and a new model of sediment transport that takes into account the fractional composition of the sediment. Using as an example a concrete reservoir located on a mountain river, it is shown that it is extraordinarily important to take into account the heterogeneity of the soil in the process of solving these types of problems. A combination of the annual hydraulic flushing of reservoirs and mechanical removal of soil from the accumulation basins together assure the required useful volume throughout the entire service life of the hydroelectric plant, though it requires the annual removal of up to 40% of the sediment discharge of the river.

Understanding the long‐term evolution of estuarine shoals given natural variations and human modifications is a key issue for wetland protection and shoal management. Here, the multi‐decadal (1958–2013) morpho‐sedimentary dynamics of the Nanhui Shoal (NHS), the largest Changjiang estuarine marginal shoal, are studied using a suite of hydrological, sedimentological, and bathymetric data. The results show that the tidal flow regime and sedimentary mode around the NHS changed slightly after the 1980s. Moreover, the NHS experienced a siltation‐induced volume increase of 4.1 × 10⁸ m³, concentrated in the landward region, and seaward progradation, producing an increase in gross area of 33 km², during 1958–2013. Even so, the actual tidal flat resource decreased by 29% due to the reclamation of 202 km². Transition in the development of the NHS is detected: a planar geometry transformation from a triangular cusp to an arcuate cusp during 1958–1989; vertical siltation in the landward region under a stable arcuate‐shaped geometry thereafter. Furthermore, a steeply sloping profile with grades of 2–11‰ formed in the northern section, which limits future reclamation to 80 km² there. Estuarine regime adjustment, inducing hydrodynamic alterations in the South Passage, dominated the geometric changes in the NHS during 1958–1989, whereas substantial siltation promotion projects led to the landward siltation after 1989. The decrease in sediment input downstream of the Three Gorges Dam has played a minor role in the shoal evolution. This work provides new insights into the long‐term morpho‐sedimentary responses of estuarine shoals to natural and artificial forcings and their implications for shoal exploitation.

Land use/land cover change (LUCC) combined with gold mining activity (GMA) have reportedly affected the water quality of Amazonian rivers by intensifying surface soil erosion and increasing rivers’ sediment concentration (SC). However, the role of LUCC on river siltation in comparison to that caused by GMA has not been assessed, and predictions of SC in the rivers accounting for future LUCC are scarce. This study applied a sediment modeling approach on Crepori Basin, located at eastern Amazon Basin, to simulate the impacts of past and future LUCC on SC in the river, comparing their impacts to those caused by GMA. Between 1973 and 2012, the expansion of deforested areas in the region had increased sheet erosion-driven SC in the river, especially during the high-water season, by up to 73.3%. LUCC projections for 2050 suggest future increases in sheet erosion-driven SC during the high-water season by more than three times of that caused by the land cover scenario of 1998–2012. Comparison between SC driven by sheet erosion to that caused by GMA has also shown that during the high-water and the low-water seasons, respectively, only about 14% and 6% of the total SC in the Crepori River resulted from laminar soil erosion, with the remaining proportion resulting from GMA.

Quantitative information on sediment sources is useful for developing targeted protection measures that effectively control soil erosion in a watershed. In this study, a multiple composite fingerprints method was tested and used for quantifying the sediment provenance of the Danghe River, and for providing effective sediment control strategies for the watershed in an arid region experiencing both wind and water erosion. Surface samples were taken from three geomorphic source areas of dunes, gobi, and upstream mountains; and sediment samples from the watercourses near the reservoir. To accommodate the wide range of sediment size distributions resulting from the fluvial and aeolian processes, sediment contributions from each source were estimated for each of six particle size groups. The results showed that the proportional contributions from each source to the reservoir sediments were 56.73% from upstream mountains, 26.36% from gobi, and 16.91% from dunes, with the relative contributions in each size group following a similar trend. The largest fraction of the sediment was from the 0.063–0.1 mm particle size group, accounting for about 37.09% of the total, in which 4%, 7.59%, and 25.50% were from dunes, gobi, and upstream mountains. Our results also indicated that selective erosion existed in both erosion processes, especially in wind erosion process, and multiple particle size tracking should be used in the cases of severe selective erosion to improve the accuracy of estimation. Also, the sediment contribution rate per unit area was the largest from dunes; thus, controlling wind-blown sand to the river by stabilizing the dunes is recommended to reduce the reservoir siltation.

The estuarine delta of the Yellow River is a region of strong land-ocean-human interactions that undergoes a unique evolutionary process. In this paper, we combined historical data and remote sensing images to better understand the evolution of the Yellow River delta. Changes in the Yellow River estuarine flow path from natural swing to artificial diversion were first studied to understand the rules and mechanism of the delta formation. The complex geomorphic structural system of the Yellow River delta is constituted by contemporary and modern deltas and their sub-deltas. Remote sensing images and measured data indicate that variations in runoff and sediment load in the Yellow River estuary will affect the deltaic erosion and siltation. The natural and artificial factors that cause runoff and sediment changes include climate change, soil erosion control in the middle reaches, building reservoirs along the Yellow River, which are used as water supply for local cities and farmland irrigation, as well as the water and sediment regulation experiment in the Xiaolangdi reservoir. Furthermore, artificial intervention of diversion channels has contributed to the maintained stability of the Yellow River estuary environment, so as to have regional development and prosperity of the Yellow River delta.

There are about 66 tributaries distributed in the Three Gorges Reservoir (TGR) area. As obvious deposition has been observed at estuary of most tributaries estuary since the water-impoundment of TGR, the possibility of sedimentation leading to form entrance bar at estuary of tributaries should be highly concerned. Based on data of topography and cross-sections, the DEM digital elevation model is established to calculate the aggradation volume at the estuary of tributaries in TGR, also the scouring and silting thickness at estuary will be demonstrated. Changes of cross-sections and thalweg caused by aggradation are also studied. The results show that: (1) The aggradation volume at estuary of 66 tributaries in TGR was 180 million m3 from March 2003 to November 2011; (2) hydrodynamic conditions at estuary of tributaries weakened after the operation of TGR, which is the root cause of sediment deposition. The extent of sediment silting was affected by sediment from the tributaries and backward water from the mainstream, meanwhile the dynamic state of river course at estuary had an important influence on the range of aggradation; (3) sediment deposited at the estuary mainly derived from backward water of mainstream, and less from the tributaries. As sediment concentrations both in mainstream and tributaries decreased obviously and will be continually maintain a low level, there is little risk for the formation of entrance bar of tributaries in TGR.

Arid and semi-arid regions face multiple problems in terms of water management, particularly where surface water is a primary resource. On the northern flank of the High Atlas Mountains (Morocco), deforestation has resulted in soil erosion and siltation of reservoirs. Better characterization of sediment yield is important for reducing the impact of siltation and prolonging the lifespan of dams. The Soil and Water Assessment Tool was used for modeling the N′fis basin in the southern Tensift watershed, leading to a better understanding of the rate of siltation behind Lalla Takerkoust dam. Runoff and sediment yield simulations were evaluated using graphical and statistical methods. The SWAT model performed well in estimating sediment load during the calibration period from 1990 to 2015 (Nash–Sutcliffe efficiency = 0.5–0.62, R2 = 0.5–0.61). The model enabled the determination of soil loss within each hydrological response unit in the watershed. The overall rate was approximately 123 t Ha−1 for an average annual rainfall of 315 mm yr−1. This high yield has to be taken into account for effective water-resources management in the N′fis basin.

The distribution, structure, and dynamics of the bottom communities of the Kerch Strait macrozoobenthos were studied based on an analysis of literary sources in 1934 and 1955, archival data of hydrobiological field studies by the Southern Research Institute of Marine Fisheries and Oceanography (YugNIRO, Kerch) in 1986 and 1989, and the results of a joint Russian–Ukrainian benthic survey of the Kerch Strait (47 stations) carried out by the Institute of Geography, Russian Academy of Sciences (RAS), and YugNIRO in summer 2010. It has been revealed that over the past 75 years, populations of bivalve filter-feeding mollusks (sestonophages) have degraded in the strait’s ecosystem, whereas populations of polychaetes (detritovorous collectors) preferring silty beds have increased. Species of benthic animals and areas of the strait in which maximum changes have occurred have been identified. After analyzing the dynamics of the structure of bottom sediments in the strait based on the archival YugNIRO data and the results of a diving survey by IG RAS in 2008 (49 dives), it was proved that one reason for the established transformations was silt deposition in a significant part of the floor of the strait as a result of previous (burial of dredged sediments, 1960–1990 ) and modern (construction of the Tuzla dam, 2003) economic activity. Since the character of the recorded transformations prevents the assumption of these reasons as unique, the authors consider various hypotheses explaining the mechanism for these changes. A conclusion is drawn about the need for further research on the geoecological dynamics of the Kerch Strait ecosystem, especially today, after construction of the Crimean Bridge.

Reservoir siltation surveys facilitate the quantification of the mean area-specific sediment yield (SSY) of catchments for decadal and longer time spans. This requires information on the volume (VS) and dry bulk density (dBD) of reservoir deposits, the period of time (TR) during which they were accumulated, the reservoir sediment trap efficiency (TE) and the catchment area (A). For the calculation of the catchment-wide average rate of erosion by water (E), the sediment delivery ratio (SDR) of the catchment needs to be estimated. Each step in this workflow represents a potential source of uncertainty. Here, we explore the extent to which individual error sources contribute to uncertainties in SSY and E values. Mean SSY and E values are inferred for small to medium-sized catchments (≤100 km2) of 15 small (≤350 × 103 m3) intermittently dry reservoirs located in the southern Kruger National Park and observation periods of 30 to 65 yr. Mean relative uncertainties of resulting SSY and E values amount to ±21% and ±46% at the 95% confidence level, respectively. Uncertainties in SSY values arise mainly from the TE estimation (mean fractional uncertainty contribution of 64%), while the SDR estimation is the major cause (79%) for uncertain E values. Uncertainties in the determination of VS and dBD values are rather unimportant, contributing together