排序方式： 共有5条查询结果，搜索用时 15 毫秒
1
1.
Krishnamoorthy Lakshmi Ammal Priya Soufiane Haddout Joan Cecilia Catubig Casila 《国际泥沙研究》2022,37(2):248-257
Water depth,salinity,current,and suspended sediment concentration(SSC)were measured along with the grain size distribution of bed sediment along an estuarine longitudinal section.The floc size increased with increase in the percentage of clay and silt,while decreased with increase in the percentage of sand content of bed sediment.The turbulent shear,G,had a direct effect on floc size with its value increasing with increase in G up to a G value of 15 s-1,while an inverse relation existed between floc size and G at higher G(G>15 s-1).Further,higher turbulence enabled sand to get resuspended and cause additional shear leading to the break-up of flocs.An attempt was made to modify G to account for the combined effect of water turbulence(G)and shear imparted by sand(Ga)and the impact of the modification of G on the predictability of floc size was evaluated.A new model was developed which explains floc size in terms of sediment concentration(C),salinity gradient(S),and G for different scenarios based on the value of G.Sensitivity analysis was done for observed floc size(FS)and predicted floc size using four approaches:(I)FSαCx;(II)FSαCxS-y;(III)FSαCxS-yGz for G<15 s-1and FSαCxS-yG-z for G>15 s-1;and(IV)FSαCxS-yGm-zfor G>15 s-1and Gm=G+Ga,where x,y,and z are determined by calibration.It was observed that the predictability of the floc size improved when the turbulence was modified to account for shear imparted by sand so that the coefficient of determination was increased from 0.78 for model III to 0.89 for model IV.Further,the settling velocity was expressed as a function of suspended sediment concentration,turbulent shear,and salinity gradient.The predictability of settling velocity was improved(R2 increased from 0.77 to 0.86)when the additional turbulence created by sand was incorporated in the non-dimensional empirical equation.The study highlights the influence of sand in causing the break-up of flocs and suggests that for turbulence shear values high enough to resuspend sand,and G has to be modified to account for the additional shear imparted by sand in mixed sediment estuarine environments. 相似文献
2.
《国际泥沙研究》2021,36(6):723-735
This numerical modeling study (i) assesses the influence of the sediment erosion process on the sediment dynamics and subsequent morphological changes of a mixed-sediment environment, the macrotidal Seine estuary, when non-cohesive particles are dominant within bed mixtures (non-cohesive regime), and (ii) investigates respective contributions of bedload and suspended load in these dynamics. A three dimensional (3D) process-based morphodynamic model was set up and run under realistic forcings (including tide, waves, wind, and river discharge) during a 1-year period. Applying erosion homogeneously to bed sediment in the non-cohesive regime, i.e., average erosion parameters in the erosion law (especially the erodibility parameter, E0), leads to higher resuspension of fine sediment due to the presence of coarser fractions within mixtures, compared to the case of an independent treatment of erosion for each sediment class. This results in more pronounced horizontal sediment flux (two-fold increase for sand, +30% for mud) and erosion/deposition patterns (up to a two-fold increase in erosion over shoals, generally associated with some coarsening of bed sediment). Compared to observed bathymetric changes, more relevant erosion/deposition patterns are derived from the model when independent resuspension fluxes are considered in the non-cohesive regime. These results suggest that this kind of approach may be more relevant when local grain-size distributions become heterogeneous and multimodal for non-cohesive particles. Bedload transport appears to be a non-dominant but significant contributor to the sediment dynamics of the Seine Estuary mouth. The residual bedload flux represents, on average, between 17 and 38% of the suspended sand flux, its contribution generally increasing when bed sediment becomes coarser (can become dominant at specific locations). The average orientation of residual fluxes and erosion/deposition patterns caused by bedload generally follow those resulting from suspended sediment dynamics. Sediment mass budgets cumulated over the simulated year reveal a relative contribution of bedload to total mass budgets around 25% over large erosion areas of shoals, which can even become higher in sedimentation zones. However, bedload-induced dynamics can locally differ from the dynamics related to suspended load, resulting in specific residual transport, erosion/deposition patterns, and changes in seabed nature. 相似文献
3.
DE SUTTER R. HUYGENS M. and VERHOEVEN R. Hydraulics Laboratory Ghent University Sint-Pietersnieuwstraat Ghent Belgium. 《国际泥沙研究》2001,16(1)
l INTRODUCTIONThe theories and formulas of sediment dynamics were established based on steady and uniform flows.These theories and formulas often fail to aPply in engineering projects because, in nthee, sediment istransported often by unsteady and non-uniform fiows (Wang et al., l997).TWo cases ofnon-stationarity can be distinguished f long-tertn and short-term (Plate, l994). Long-termnon-stationarity tfansport can be defined as a sediment process which can be treated by sequences ofstat… 相似文献
4.
Our proposed three-dimensional dam breach model is tested using one field test from the European Community funded IMPACT project. Results show that this three-dimensional model accurately predicts the peak breach discharge and final breach width for this case. It is shown that the three-dimensional model is capable of simulating the breaches that develop in different locations along a hypothetical long non-cohesive dam while accounting for variations in the natural valley topography, including symmetrical and asymmetrical settings. Our results show that both the breach location and reservoir shape have a significant effect on the peak breach discharge and the outflow hydrograph shape. Different inflow hydrographs were found not to significantly change the peak breach discharge rate for the hypothetical reservoir and spillway. Comparisons with laboratory and field dam breach tests and one historically breached dam show that the real shape of the breach channel during the breach process is successfully modeled. 相似文献
5.
A coupled routing for the transport capacity and the energy slope is introduced through the definition of the control factor m whose value is linked to the bed form configuration.The coupling aims to further incorporate the interactions occurring in alluvial rivers and thus enhance the prediction of the fine sediment fluxes,especially during high stream power events.Based on a predictive rule for the control factor m that only involves water depth,velocity and bedform constitutive texture,the novel method is confronted to observations collected in one of the most strongly dynamic alluvial river namely the Lower Yellow River.Comparisons between time series of measured and computed concentrations illustrate that during high velocity events the main dynamics of the sediment transport is correctly reproduced.The main advantage of the present approach is to supply consistent time evolutions of sediment concentrations without making use of any detailed shear information. 相似文献
1