Deposition and Erosion

River morphology is one of the most important fields of river engineering and the study of the changes in the flow direction and cross-sections of a river. Over the past years, using the unique properties of remote sensing (RS) and satellite images, many studies have been conducted on rivers' morphological changes. In this study, the morphological changes of the river boundary displacement and the changes in river width resulting from deposition and erosion during 30 years period (1985 to 2015) in the Bazoft River, one of the North sub-basins of the Karun River basin in Iran, using 26 satellite images of TM, ETM + , and OLI Landsat in the ENVI 5.3 and ArcGIS 10.3 software have been assessed. The results indicated that the greatest change in the river bank takes place in the distance between 62 and 84 km from Karun-4 Dam to the upstream. Besides, analyzing long-term periods indicated that in the time intervals of 1985-1994, 1994-2005, and 2005-2015 the sediment had deposited along river banks. For 30 years, the river's average deposition and erosion levels areas are estimated to be 69.4 and 42.4 ha, respectively, meaning that ground with 27.1 ha is formed by virtue of deposition. According to the assessments, it was indicated that there is no significant difference between average deposition and erosion on the left bank in short periods, and the deposition bank is approximately 2% greater than bank erosion. However, on the right bank, the deposition level is approximately 8% greater than erosion, which is significant at a confidence level of 95%. The results of this study perfectly indicated the ability of sub-pixels and the use of water indicators in revealing the river form changes using Satellite Images Time Series (SITS).

River morphology is one of the most important fields of river engineering and the study of the changes in the flow direction and cross-sections of a river. Over the past years, using the unique properties of remote sensing (RS) and satellite images, many studies have been conducted on rivers' morphological changes. In this study, the morphological changes of the river boundary displacement and the changes in river width resulting from deposition and erosion during 30 years period (1985 to 2015) in the Bazoft River, one of the North sub-basins of the Karun River basin in Iran, using 26 satellite images of TM, ETM + , and OLI Landsat in the ENVI 5.3 and ArcGIS 10.3 software have been assessed. The results indicated that the greatest change in the river bank takes place in the distance between 62 and 84 km from Karun-4 Dam to the upstream. Besides, analyzing long-term periods indicated that in the time intervals of 1985-1994, 1994-2005, and 2005-2015 the sediment had deposited along river banks. For 30 years, the river's average deposition and erosion levels areas are estimated to be 69.4 and 42.4 ha, respectively, meaning that ground with 27.1 ha is formed by virtue of deposition. According to the assessments, it was indicated that there is no significant difference between average deposition and erosion on the left bank in short periods, and the deposition bank is approximately 2% greater than bank erosion. However, on the right bank, the deposition level is approximately 8% greater than erosion, which is significant at a confidence level of 95%. The results of this study perfectly indicated the ability of sub-pixels and the use of water indicators in revealing the river form changes using Satellite Images Time Series (SITS).

A blunt obstacle in the path of a rapid granular avalanche generates a bow shock (a jump in the avalanche thickness and velocity), a region of static grains upstream of the obstacle, and a grain-free region downstream. Here, it is shown that this interaction is qualitatively altered if the incline on which the avalanche is flowing is changed from smooth to rough. On a rough incline, the friction between the grains and the incline depends on the flow thickness and speed, which allows both rapid (supercritical) and slow (subcritical) steady uniform avalanches. For supercritical experimental flows, the material is diverted around a blunt obstacle by the formation of a bow shock and a static dead zone upstream of the obstacle. Downslope, a grain-free vacuum region forms, but, in contrast to flows on smooth beds, static levees form at the boundary between the vacuum region and the flow. In slower, subcritical, flows the flow is diverted smoothly around the dead zone and the obstacle without forming a bow shock. After the avalanche stops, signatures of the dead zone, levees and (in subcritical flows) a deeper region upslope of the obstacle are frozen into the deposit. To capture this behaviour, numerical simulations are performed with a depth-averaged avalanche model that includes frictional hysteresis and depth-averaged viscous terms, which are needed to accurately model the flowing and deposited regions. These results may be directly relevant to geophysical mass flows and snow avalanches, which flow over rough terrain and may impact barriers or other infrastructure.

Oil spills in estuaries are less studied and less understood than their oceanic counterparts. To address this gap, we present a detailed analysis of estuarine oil spill transport. We develop and analyse a range of simulations for the Humber Estuary, using a coupled hydrodynamic and oil spill model. The models were driven by river discharge at the river boundaries and tidal height data at the offshore boundary. Satisfactory model performance was obtained for both model calibration and validation. Some novel findings were made: (a) there is a statistically significant (p < 0.05) difference in the influence of hydrodynamic conditions (tidal range, stage and river discharge) on oil slick transport; and (b) because of seasonal variation in river discharge, winter slicks released at high water did not exhibit any upstream displacement over repeated tidal cycles, while summer slicks travelled upstream into the estuary over repeated tidal cycles. The implications of these findings for op...

This paper summarises the work done on the distribution and reactivity of organic contaminants (simazine, atrazine, lindane, ¯uoranthene, pyrene, PCB 77, PCB 118) in the Humber Estuary and associated major rivers, as part of the LOIS programme. The preliminary ¯ux calculations show that the most important contributors of selected organic contaminants were the rivers Trent (45% of simazine, 20% of atrazine), Aire (30% of simazine and 33% of atrazine), Don (36 and 37% of ¯uoranthene and pyrene) and Ouse (18% of ¯uoranthene and pyrene). For lindane and PCBs, the Aire and Ouse were the key sources. The water ¯ow in all the rivers shows strong seasonal variations, as do the contaminant concentrations. As a result, the mean daily ¯uxes of these contaminants displayed a strong seasonality. Annual mean concentrations of simazine and atrazine decreased by more than 50% over the period 1994±1995 in most of the rivers, probably as a result of their restricted use in the UK. Mass balance calculations show that the Humber is a sink for atrazine, lindane, PCB 77 and PCB 118, although the degree of removal is generally much lower for atrazine and lindane than for PCB 77 and PCB 118. Mass balance results also show that the Humber can either be a source of ¯uoranthene and pyrene (in the suspended particulate phase), or a sink (in the dissolved phase), although overall the Humber acts as sink. The budget exercise represents an attempt to quantify the input and output of selected organic contaminants from catchment to ocean. However, due to limited data and assumptions involved in calculations, the estimates should be considered as an order of magnitude approximation. Further improvement both in resolution and accuracy is required.

A computational algorithm is proposed for steady oceanographic flows in which the two-dimensional shallow-water equations are coupled to a separate integration in the vertical direction. The algorithm is much more efficient than the conventional three-dimensional schemes. For a simple test model the results agree well with previous results published by Davies and Owen. 1

AbstractÐAggregation and sedimentation of particles in lakes, estuaries, settling basins and the deep ocean play a central role in biological cycles, fate and movement of contaminants, and trace element transport. Relative quiescence with continuous in¯ux characterizes these and other aqueous environments. However, our understanding of the processes of aggregation and sedimentation in these vital systems is poor. Inadequate experimental systems and measuring instrumentation are primary causes of this shortcoming. This paper details a laboratory experimental system which creates a continuous¯ow, quiescent microcosm in which particle aggregation and settling can be studied. The system's functioning and quiescence has been rigorously veri®ed and the conditions for successful operation de®ned. A model is detailed which describes¯uid and solute movement in the experimental system. The results of the system veri®cation studies indicate signi®cant¯uid mixing may occur in experimental systems which are assumed to be quiescent, yet where no careful temperature management has been employed. This unexpected and uncontrolled¯uid motion may lead to signi®cant errors in experiments whenever particles smaller than about 20 microns with environmentally relevant densities are studied. #

Abstract: Details are given of a combined physical and numerical
model study of sediment transport processes in a square harbour caused by tidal motion. The effects on bed level changes due to tidal currents and the configuration of the harbour entrance were investigated. A lightweight material called Cation Resin was used in this study to represent bed sediments in the laboratory experiments.
This material enabled the erosion and deposition processes to be exaggerated within the model harbour, in which the magnitude of the flow velocities was relatively small. An unstructured mesh generation technique, namely a quad-tree grid, was incorporated into an existing
two-dimensional depth-integrated numerical model to predict the transport of water quality constituents and sediment particle fluxes. The numerical model was further refined to include the prediction of bed level changes.
Detailed comparisons between the numerical model predictions and the laboratory data were undertaken. It was found that the numerical model predictions and the laboratory measurements were in good agreement. It was also concluded that Cation Resin was an appropriate
material to use for physical modelling of sediment transport processes in laboratory model studies.

Cohesive sediment related problems in estuaries include shoaling in navigable waterways and water pollution. A two-dimensional, depth-averaged, finite element (FE) cohesive sediment transport model, CSTM-H, has been developed and may be used to assist in predicting the frequency and quantity of dredging required to maintain navigable depths and the fate of adsorbed pollutants. Algorithms which describe the processes of erosion, dispersive transport, deposition, bed formation and bed consolidation are incorporated in CSTM-H. The Galerkin weighted residual method is used to solve the advection-dispersion equation with appropriate source/sink terms at each time step for the nodal suspended sediment concentrations. The model yields stable and converging solutions. Partial verification was carried out against a series of erosion-deposition experiments in the laboratory using kaolinite and a natural mud as sediment. Model applications under prototype conditions are described.

Details are given of a re®ned, three-dimensional, layerintegrated mathematical model for predicting accurately the¯ow and cohesive sediment transport processes in estuarine and coastal waters. The model is applied to the Humber Estuary, UK, in order to predict the suspended cohesive sediment transport¯uxes. Field-measured data at a station in the Trent Falls region (53°42.8 H N, 0°3 7.8 H W) and Station SG13 in the plume region (53°3 5.19 H N, 0°13.90 H E) were used to drive the model. Comparisons between the model predictions and ®eld-measured data at Station SG23 (53°35.71 H N, 0°02.17 H E) within the estuary (Hawke Anchorage) were made. Comparisons of the suspended cohesive sediment concentrations for the numerical model results and the ®eld data at Hawke Anchorage showed good agreement in the regime of deposition. In the regime of erosion, the model also gave reasonably good predictions, although the large variation in suspended sediment concentrations with depth was not well reproduced by the numerical model. Ó

Abstract
Details are given of a refined, three-dimensional, layer-integrated mathematical model for predicting accurately the flow and cohesive sediment transport processes in estuarine and coastal waters. The model is applied to the Humber Estuary, UK, in order to predict the suspended cohesive sediment transport fluxes. Field-measured data at a station in the Trent Falls region (53° 42.8′N, 0° 37.8′W) and Station SG13 in the plume region (53° 35.19′N, 0° 13.90′E) were used to drive the model. Comparisons between the model predictions and field-measured data at Station SG23 (53° 35.71′N, 0° 02.17′E) within the estuary (Hawke Anchorage) were made. Comparisons of the suspended cohesive sediment concentrations for the numerical model results and the field data at Hawke Anchorage showed good agreement in the regime of deposition. In the regime of erosion, the model also gave reasonably good predictions, although the large variation in suspended sediment concentrations with depth was not well reproduced by the numerical model.

Abstract
A refined three-dimensional layer-integrated model to predict accurately salt and cohesive sediment transport in estuarine waters is described herein. A splitting algorithm has been used to split the three-dimensional transport equation into a horizontal two-dimensional equation and a vertical one-dimensional equation due to the different length scales. An additional source term associated with the layer average of the free-surface flow is introduced in the conservative form of the layer-integrated pollutant transport equation. The one-dimensional QUICKEST scheme has been extended to two dimensions and included in the layer-integrated advective–diffusion equation. A modified one-dimensional ULTIMATE algorithm has also been added to avoid unphysical numerical oscillations. Numerical tests for discontinuities have been carried out to study the performance of the ULTIMATE QUICKEST scheme used in the present model. The model has also been used to simulate solute transport in an idealized harbor. It has been found that the additional source term was crucial for the mass conservation of pollutant. Finally the refined model has been applied to simulate salt and cohesive sediment transport in the Humber Estuary, UK. Good agreement has been obtained with the field measured data.

Abstract
Details are given of a combined physical and numerical model study of sediment transport processes in a square harbour caused by tidal motion. The effects on bed level changes due to tidal currents and the configuration of the harbour entrance were investigated. A lightweight material called Cation Resin was used in this study to represent bed sediments in the laboratory experiments. This material enabled the erosion and deposition processes to be exaggerated within the model harbour, in which the magnitude of the flow velocities was relatively small. An unstructured mesh generation technique, namely a quad-tree grid, was incorporated into an existing two-dimensional depth-integrated numerical model to predict the transport of water quality constituents and sediment particle fluxes. The numerical model was further refined to include the prediction of bed level changes. Detailed comparisons between the numerical model predictions and the laboratory data were undertaken. It was found that the numerical model predictions and the laboratory measurements were in good agreement. It was also concluded that Cation Resin was an appropriate material to use for physical modelling of sediment transport processes in laboratory model studies.