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Abstract: Sediment transport processes in rivers continue to pose a challenge when designing movable-bed physical models, particularly for reproducing the grain sorting and bank erosion (fluvial erosion and mass failure). This paper presents and discusses scale effects of a specific scaling approach for multi-grain size mixtures that preserves similarity of initial motion for each grain size class and of the bank stability coefficient between the model and the prototype, but relaxes strict similarity of the Shields and particle Reynolds numbers. This approach is appropriate when bed load transport near incipient motion conditions is being studied, and allows for larger grain size scales than when full Shields parameter similarity is enforced. As part of an environmental project to rehabilitate sediment transport through bank erosion, this method has been applied to scale a Froude number criterion physical model of a reach of the Old Rhine (France). This has resulted in an undistorted scale of 40, and the use of sand as the model bank material. Each grain size has a different geometrical scale. The time scale for sediment motion is grain size and flow discharge dependent. An average time scale of 6 has therefore been used (four model hours = one prototype day). A strategy devised for the field case consists of two higher, larger island groynes that replace the three existing groynes, producing bank erosion for flow rates below the mean annual flow rate. Extrapolation of model behaviour to the prototype is not a major problem, but the volume of eroded bank material may be underestimated, mainly because of the relaxation of the Shields number similarity and the apparent cohesive properties of the model bank material. [Copyright &y& Elsevier]

Abstract: The Blue Nile supplies the Nile River with the largest proportion of water and sediment. Nevertheless, very few, often contrasting data are reported in the literature about its sediment yield. This paper deals with detailed field measurement of suspended sediment transport taken at Khartoum during three flood seasons in the late 1960s. The pattern of suspended sediment concentration, discharge and grain-size variation with flow is analysed and suspended sediment yield is calculated and compared with data from different sources. No bedload transport measurements are reported in the literature for the Blue Nile. The flow data measured in the field consent to select several dune geometry criteria and to adopt the dune bedforms migration method to calculate bedload transport. The same procedure is applied also to the bedload data measured in four reaches of the Nile River, downstream of the High Aswan Dam, with channel and sediment characteristics comparable with those of the Blue Nile at Khartoum, to ascertain which dune geometry criterion provided the most reliable results. The and equations predict similar values of bedload transport that are compared with the very few bedload data assessed by other authors using different equations and methods. Finally, a good relation between flow velocity and bedload transport rate is found. [ABSTRACT FROM AUTHOR]

Abstract: Sediment output (solid and dissolved load) from two small Alpine rivers (Partnach and Lahnenwiesgraben in the Bavarian Alps) was measured during three summer field seasons from 2001–2003. There is high spatial variability of sediment output between the catchments and a high temporal variability between observation periods. Sediment transport in the Partnach river (Reintal) is dominated by solute load, whereas the Lahnenwiesgraben river transports a much greater proportion of solid load. This difference can mainly be explained by the different lithologies of the systems. The Reintal catchment is dominated by massive Triassic limestone. In the Lahnenwiesgraben catchment, in addition to limestones, unconsolidated rocks, marls and mudstone layers are significant. Furthermore, large rockslide dams in the Partnach valley isolate large parts of the Reintal catchment from solid load output. The components of fluvial sediment transport were, where possible, calculated by using flow duration curves and rating curve techniques. In the Lahnenwiesgraben event specific rating curves were used to determine suspended load. On the broad database of 55 measured flood events in the Lahnenwiesgraben a good correlation (r Pearson =0.9) between event peak discharge and suspended load of the event was established. Effective discharge was calculated for the different types of sediment load (solid and dissolved) and total load. In the Reintal effective discharge for total load is found in low flow classes close to mean discharge, because sediment output is dominated by dissolved load, which has its maximum efficiency at low and moderate discharges. In the Lahnenwiesgraben most work is done by discharges much higher than mean discharge during extreme individual flood events. [Copyright &y& Elsevier]

Abstract: The erosion behaviour of various fine-grained sediment deposits has been investigated in laboratory experiments. This work mainly focused on tests using sewer sediment in which strong biochemical reactions were observed during the deposit formation period. A small number of initial tests were conducted in which the deposits were made from mixtures of “clean” mineral and organic sediments. The erosion behaviour observed in these tests was compared with the erosion characteristics for sediments taken from deposits in a sewer. The impact of the biological processes on physical properties such as bulk density, water content, deposit structure and the erosive behaviour as a function of bed shear stress are quantified and discussed. Based on these observations it is believed that bio-processes weaken the strength of the in-pipe sediment deposits. A significantly weaker sediment surface layer was observed during deposition under quiescent oxygen-rich conditions. This resulted in a deposit with low shear strength which may be a cause of a first foul flush of suspended sediment when flow rates were increased. Comparison between tests with sewer sediments and the artificial representative surrogates suggested that the deposits of the later did not correctly simulate the depositional development and the resultant erosion patterns observed with the more bio-active sewer sediment. [Copyright &y& Elsevier]