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971.
Vertical profiles of fluid velocity and suspended sediment concentration in nearshore 总被引:2,自引:0,他引:2
Based on the power function of velocity and the friction velocity,a velocity profile is obtained.By solving the Schmidt’s diffusion equation,an equilibrium suspended sediment concentration profile is further deduced.The profiles of velocity and suspended sediment concentration agree well with the field data,and the profile of suspended sediment concentration avoids the unreasonableness of the classical Rouse profile such as a zero value at the water surface.According to these profiles,an expression which is easy to use for calculating the suspended sediment transport rate is derived. 相似文献
972.
Three different methods to analyse fine sediment deposits on a gravel bar using pictures are presented in this paper. A manual digitization and deposits zone delineation are performed as well as two different automated procedures. The three methods are applied on aerial pictures taken in 2006 by a drone from a height around 150 m above the study site. Two other sets of pictures taken in 2010 are also studied: the first set was obtained from the left side bank of the river at approximately 15m above the gravel bar whereas the second one was taken from a helicopter flying 600~m above the ground. These methods were used to estimate the surface of fine sediment deposits before and after flushing events. They yield similar results even if the first automated procedure is able to capture smaller patches of fine sediments. The total surface of fine sediment deposits seems to be similar before and after a flushing event, but the distribution appears quite different. Before a flushing event, a significant amount of fine sediment deposits are mixed with coarser sediments. After the flushing event, one can observe more large fine sediment deposits located on the downstream part of the secondary channel and at the channel margin. Most of the small fine sediment deposit patches were washed out. A short discussion is provided on the possible dynamics of fine sediment deposits over the gravel bar. 相似文献
973.
A. Tazioli 《水文科学杂志》2013,58(7):1314-1324
Abstract Discharge measurements in natural watercourses are performed in order to determine the value of the surface outflow of a basin, its temporal variability, and the outflow characteristics. The methods conventionally used for these measurements utilize an immersed current meter in different points of a river section, which acquires the mean flow velocity. Using this measurement, the discharge can be calculated. Some experimental problems arise, however, when there is a very high discharge. An important method, valid in such cases, is the artificial tracing method. In particular, the use of chemical tracers for small watercourses is very convenient because they are low cost, easily handled, low impact and provide satisfactory results. In the past, radioactive tracers such as tritium have been used in large rivers, while fluorescent tracers have been commonly exploited in the USA and now elsewhere. However, if the water is turbid, the suspended sediments may easily absorb some tracers. In this paper, the preliminary results of a comparison between current meter and artificial tracer measurements are reported. In particular, field tests in a small tributary have been performed, in order to investigate the behaviour of different tracers. Citation Tazioli, A. (2011) Experimental methods for river discharge measurements: comparison among tracers and current meter. Hydrol. Sci. J. 56(7), 1314–1324. 相似文献
974.
Abstract This paper presents a reach-scale sediment balance of a large impounded Mediterranean river (the lower Ebro, 1998–2008). Multi-temporal sediment storage and the influence of floods and tributaries on the sediment load were examined using continuous discharge and turbidity records. The mean annual suspended sediment load at the reach outlet (Xerta) is 0.12?×?106 t, corroborating previous results. Suspended sediment concentrations were low (SSCmean?=?13 mg L-1), attaining a maximum of 274 mg L-1. Erosion processes (channel-scour, bank erosion) are dominant, and net export of sediment occurs over the long term. Unexpectedly, ephemeral tributaries were found to contribute significantly: sediment delivered during torrential events attained 5% of the Ebro annual load, and was even larger than that in flushing flows. Overall, most of the suspended sediment load is transported by floods (up to 65% in some years). The results constitute basic information to underpin current management actions aiming to achieve the sustainability of the riverine and deltaic system. Editor D. Koutsoyiannis; Associate editor D. Hughes Citation Tena, A., Batalla, R.J. and Vericat, D., 2012. Reach-scale suspended sediment balance downstream from dams in a large Mediterranean river. Hydrological Sciences Journal, 57 (5), 831–849. 相似文献
975.
M.E. Grismer 《水文科学杂志》2013,58(5):878-900
Abstract Recent developments in hydrological modelling of river basins are focused on prediction in ungauged basins, which implies the need to improve relationships between model parameters and easily-obtainable information, such as satellite images, and to test the transferability of model parameters. A large-scale distributed hydrological model is described, which has been used in several large river basins in Brazil. The model parameters are related to classes of physical characteristics, such as soil type, land use, geology and vegetation. The model uses two basin space units: square grids for flow direction along the basin and GRU—group response units—which are hydrological classes of the basin physical characteristics for water balance. Expected ranges of parameter values are associated with each of these classes during the model calibration. Results are presented of the model fitting in the Taquari-Antas River basin in Brazil (26 000 km2 and 11 flow gauges). Based on this fitting, the model was then applied to the Upper Uruguay River basin (52 000 km2), having similar physical conditions, without any further calibration, in order to test the transferability of the model. The results in the Uruguay basin were compared with recorded flow data and showed relatively small errors, although a tendency to underestimate mean flows was found. 相似文献
976.
977.
If increased sediment supply to a river channel exceeds its transport capacity, deposition necessarily occurs as the bed adjusts to accommodate the increased supply. Both the mean and spatial patterns in bed elevation and grain size may change and an ability to understand their relative importance is needed to predict bed response. We report on an experiment in a field‐scale flume in which sediment supply is increased to a gravel bed with alternate bars. Sediment was recirculated in the experiments, but augmented in two steps, after which the bed was allowed to reach a new steady state. The transport rate at the end of the experiment was three times larger than at the start. High‐resolution sediment flux and topographic measurements, grain size derived from photographs, and hydrodynamic modeling allow us to document the topographic and textural response of the bed to increased sediment supply. The spatial patterns of bed topography and texture were forced by the flume setup and the initial and final steady states included long stationary alternate bars with associated grain size sorting. The transient bed contained several scales of shorter wavelength migrating bedforms superimposed on, and temporarily replacing the stationary alternate bars. Bed topography and textural patterns adjusted to increased sediment supply over different timescales. Bed slope and mean stress increased directly with sediment supply rate to produce a new transport steady state in a time about 2.5 times the minimum needed to deposit the required sediment wedge, indicating a trap efficiency of about 40% for the aggrading wedge. Adjustments in local topography and sorting, primarily in the form of smaller, migrating bars, continued for a period approximately equal to that required to initially reach transport steady state. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
978.
David J. Milan 《地球表面变化过程与地形》2013,38(14):1623-1641
This paper provides comprehensive evidence that sediment routing around pools is a key mechanism for pool‐riffle maintenance in sinuous upland gravel‐bed streams. The findings suggest that pools do not require a reversal in energy for them to scour out any accumulated sediments, if little or no sediments are fed into them. A combination of clast tracing using passive integrated transponder (PIT) tagging and bedload traps (positioned along the thalweg on the upstream riffle, pool entrance, pool exit and downstream riffle) are used to provide information on clast pathways and sediment sorting through a single pool‐riffle unit. Computational fluid dynamics (CFD) is also used to explore hydraulic variability and flow pathways. Clast tracing results provide a strong indication that clasts are not fed through pools, rather they are transported across point bar surfaces, or around bar edges (depending upon previous clast position, clast size, and event magnitude). Spatial variations in bedload transport were found throughout the pool‐riffle unit. The pool entrance bedload trap was often found to be empty, when the others had filled, further supporting the notion that little or no sediment was fed into the pool. The pool exit slope trap would occasionally fill with sediment, thought to be sourced from the eroding outer bank. CFD results demonstrate higher pool shear stresses (τ ≈ 140 N m–2) in a localized zone adjacent to an eroding outer bank, compared to the upstream and downstream riffles (τ ≈ 60 N m–2) at flows of 6 · 2 m3 s–1 (≈ 60% of the bankfull discharge) and above. There was marginal evidence for near‐bed velocity reversal. Near‐bed streamlines, produced from velocity vectors indicate that flow paths are diverted over the bar top rather than being fed through the thalweg. Some streamlines appear to brush the outer edge of the pool for the 4 · 9 m3 s–1 to 7 · 8 m3 s–1 (between 50 and 80% of the bankfull discharge) simulations, however complete avoidance was found for discharges greater than this. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
979.
ABSTRACTSedimentation in navigable waterways and harbours is of concern for many water and port managers. One potential source of variability in sedimentation is the annual sediment load of the river that empties in the harbour. The main objective of this study was to use some of the regularly monitored hydro-meteorological variables to compare estimates of hourly suspended sediment concentration in the Saint John River using a sediment rating curve and a model tree (M5?) with different combinations of predictors. Estimated suspended sediment concentrations were multiplied by measured flows to estimate suspended sediment loads. Best results were obtained using M5? with four predictors, returning an R2 of 0.72 on calibration data and an R2 of 0.46 on validation data. Total load was underestimated by 1.41% for the calibration period and overestimated by 2.38% for the validation period. Overall, the model tree approach is suggested for its relative ease of implementation and constant performance.
EDITOR M.C. Acreman; ASSOCIATE EDITOR B. Touaibia 相似文献
980.
M. Ali Kokpinar A. Burcu Altan-Sakarya S. Yurdagul Kumcu Mustafa Gogus 《水文科学杂志》2013,58(12):2189-2203
AbstractAnalyses of data from reservoir surveys and sediment rating curves are compared to predict sediment yield in three large reservoir watershed areas in Turkey. Sediment yield data were derived from reservoir sedimentation rates and suspended sediment measurements at gauging stations. The survey data were analysed to provide the volume estimates of sediment, the time-averaged sediment deposition rates, the long-term average annual loss rates in the reservoir storage capacity, and the long-term sediment yield of the corresponding watershed areas. Four regression methods, including linear and nonlinear cases, were applied to rating curves obtained from gauging stations. Application of the efficiency test to a power function form of a rating curve with nonlinear regression yielded the highest efficiency values. Based on the analysis of the sediment rating curves, sediment load fluxes were calculated by using average daily discharge data at each gauging station. Comparison of these two sediment yield values for each reservoir showed that the sediment yields from the suspended sediment measurements, SYGS, are 0.99 to 3.54 times less than those obtained from the reservoir surveys, SYRS. The results from the reservoir surveys indicate that all three reservoirs investigated have lost significant storage capacity due to high sedimentation rates. 相似文献