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1.
Complex variations in sediment transport at three large river bifurcations during discharge waves in the river Rhine 总被引：1，自引：0，他引：1
River bifurcations strongly control the distribution of water and sediment over a river system. A good understanding of this distribution process is crucial for river management. In this paper, an extensive data set from three large bifurcations in the Dutch Rhine is presented, containing data on bed‐load transport, suspended bed sediment transport, dune development and hydrodynamics. The data show complex variations in sediment transport during discharge waves. The objective of this paper is to examine and explain these measured variations in sediment transport. It is found that bend sorting upstream of the bifurcations leads to supply limitation, particularly in the downstream branch that originates in the outer bend of the main channel. Tidal water level variations lead to cyclical variations in the sediment distribution over the downstream branches. Lags in dune development cause complex hysteresis patterns in flow parameters and sediment transport. All bifurcations show evidence of sediment waves, which probably are intrinsic bifurcation phenomena. The complex transport processes at the three bifurcations cause distinct discontinuities in the downstream fining trend of the river. Differences among the studied river bifurcations are mainly due to differences in sediment mobility (Shields value). Because the variations in sediment transport are complex and poorly correlated with the flow discharge, prediction of the sediment distribution with existing relationships for one‐dimensional models is problematic. 相似文献
2.
Sylvain Capo Isabelle Brenon Aldo Sottolichio Patrice Castaing Patrick Le Goulven 《Journal of African Earth Sciences》2009,55(1-2):52
In comparison to their temperate counterparts, sediment processes in tropical estuaries are poorly known and especially in African ones. The hydrodynamics of such environments is controlled by a combination of multiple processes including morphology, salinity, mangrove vegetation, tidal processes, river discharge, settling and erosion of mud and by physico-chemical processes as well as sediment dynamics.The aim of this study is to understand the sediment processes in this transitional stage of the estuary when the balance between river discharges and marine processes is reversing. Studying the hydrodynamics and sediment dynamics of the Konkouré Estuary has recently been made possible thanks to new data on bathymetry, sedimentary cover, salinity, water elevations, and current velocities. The Lower Konkouré is a shallow, funnel shaped, mesotidal mangrove-fringed, tide-dominated estuary, well mixed during low river discharge and stratified during high river discharge. The Konkouré Estuary is turbid despite the small amount of terrestrial input and its residual velocity at the mouth during low river discharges, landwards for two of the three branches, suggests a landward migration by tidal pumping of the suspended particulate matter. A Turbidity Maximum Zone (TMZ) is identified for typical states of the estuary with regard to fluvial and tidal components. Suspended sediment transport during a transitional stage between the rainy and dry seasons is known thanks to current velocity and Suspended Sediment Concentration (SSC) measurements taken in November 2003. The Richardson layered number calculation assesses that turbulence is the major mixing process in the water column, at least during the flood and ebb stages, whereas stratification occurs during the slack water periods. Tidal currents generate bottom erosion, and turbulence mixes the suspended sediment throughout the water column. As a result, a net sediment input is calculated from the western Konkouré outlet for two consecutive tidal cycles. Despite the net water export, almost 300 tons per tide reach the estuary through this outlet, for a moderate river flow. 相似文献
3.
钱塘江河口为强涌潮、高含沙量、河床冲淤剧烈的河口,其盐度输移时空变化受河床冲淤的反馈影响十分显著。建立了考虑河床冲淤变化的一维盐度动床数学模型,耦合求解水沙运动、河床冲淤及盐度输移过程,数值计算方法采用守恒性较好的有限体积法。验证结果表明:河床冲淤对氯度的影响非常显著,动床模型的结果与实测基本吻合,在长历时盐度预报中采用动床模型是必要的。应用该模型分析了钱塘江河口咸水入侵对上游建库、治江缩窄工程等人类活动的响应,探讨了杭州城市供水水源保证率。结果表明,新安江水库、河口治理缩窄工程对改善河口淡水资源利用、保障杭州市供水安全显著;供水保证率要达95%以上,需采取上游水库泄水调度和新建备用水库等措施。 相似文献
4.
A tidally averaged model of estuarine dynamics is used to estimate sediment transport in the Hudson River estuary over the
period 1918 to 2005. In long-term and seasonal means, along-channel gradients in sediment flux depend on the estuarine salinity
gradient and along-channel depth profile. Lateral depth variation across the estuary affects the near-bottom baroclinic circulation
and consequently the direction of net sediment flux, with generally up-estuary transport in the channel and down-estuary transport
on the shoals. Sediment transport capacity in the lower estuary depends largely on river discharge, but is modified by the
timing of discharge events with respect to the spring–neap cycle and subtidal fluctuations in sea level. Sediment transport
capacity also depends on the duration of high-discharge events relative to the estuarine response time, a factor that varies
seasonally with discharge and estuarine length. Sediment fluxes are calculated with the assumption that over long periods,
the system approaches morphological equilibrium and sediment accumulation equals sea level rise. The inferred across- and
along-channel distributions of sediment erodibility correspond with observations of bed properties. Equilibrium is assumed
at long time scales, but at annual to decadal time scales the estuary can develop an excess or deficit of sediment relative
to equilibrium. On average, sediment accumulates in the estuary during low- and high-discharge periods and is exported during
moderate discharge. During high-discharge periods, maximum export coincides with maximum sediment supply from the watershed,
but the nearly cubic discharge dependence of fluvial sediment supply overwhelms the roughly linear increase in estuarine transport
capacity. Consequently, sediment accumulates in the estuary during the highest flow conditions. Uncertainty remains in the
model, particularly with sediment properties and boundary conditions, but the results clearly indicate variability in the
sediment mass balance over long time scales due to discharge events. 相似文献
5.
6.
The Tinto and Odiel rivers drain 100 km from the Rio Tinto sulphide mining district, and join at a 20-km long estuary entering the Atlantic Ocean. A reconnaissance study of heavy metal anomalies in channel sand and overbank mud of the river and estuary by semi-quantitative emission dc-arc spectrographic analysis shows the following upstream to downstream ranges in ppm (μg g?1): As 3,000 to <200, Cd 30 to <0.1, Cu 1,500 to 10, Pb 2,000 to <10, Sb 3000 to <150, and Zn 3,000 to <200. Organic-rich (1.3–2.6% total organic carbon, TOC), sandysilty overbank clay has been analyzed to represent suspended load materials. The high content of heavy metals in the overbank clay throughout the river and estuary systems indicates the importance of suspended sediment transport for dispersing heavy metals from natural erosion and anthropogenic mining activities of the sulfide deposit. The organic-poor (0.21–0.37% TOC) river bed sand has been analyzed to represent bedload transport of naturally-occurring sulfide minerals. The sand has high concentrations of metals upstream but these decrease an order of magnitude in the lower estuary. Although heavy metal contamination of estuary mouth beach sand has been diluted to background levels estuary mud exhibits increased contamination apparently related to finer grain size, higher organic carbon content, precipitation of river-borne dissolved solids, and input of anthropogenic heavy metals from industrial sources. The contaminated estuary mud disperses to the inner shelf mud belt and offshore suspended sediment, which exhibit metal anomalies from natural erosion and mining of upstream Rio Tinto sulphide lode sources (Pb, Cu, Zn) and industrial activities within the estuary (Fe, Cr, Ti). Because heavy metal contamination of Tinto-Odiel river sediment reaches or exceeds the highest levels encountered in other river sediments of Spain and Europe, a detailed analysis of metals in water and suspended sediment throughout the system, and epidemiological analysis of heavy metal effects in humans is appropriate. 相似文献
7.
Pierre Le Hir Andre Ficht Ricardo Silva Jacinto Patrick Lesueur Jean-Paul Dupont Robert Lafite Isabelle Brenon Benedicte Thouvenin Philippe Cugier 《Estuaries and Coasts》2001,24(6):950-963
A comprehensive study of fine sediment transport in the macrotidal Seine estuary has been conducted, including observations of suspended particulate matter (SPM), surficial sediment, and bathymetric data, as well as use of a three dimensional mathematical model. Tide, river regime, wind, and wave forcings are accounted. The simulated turbidity maximum (TM) is described in terms of concentration and location according to tidal amplitude and the discharge of the Seine River. The TM is mainly generated by tidal pumping, but can be concentrated or stretched by the salinity front. The computed deposition patterns depend on the TM location and are seasonally dependent. The agreement with observations is reasonable, although resuspension by waves may be overestimated. Although wave resuspension is likely to increase the TM mass, it generally occurs simultaneously with westerly winds that induce a transverse circulation at the mouth of the estuary and then disperse the suspended material. The resulting effect is an output of material related to wind and wave events, more than to high river discharge. The mass of the computed TM remains stable over 6 months and independent of the river regime, depending mainly on the spring tide amplitude. Computed fluxes at different cross-sections of the lower estuary show the shift to the TM according to the river flow and point out the rapidity of the TM adjustment to any change of river discharge. The time for renewing the TM by riverine particles has been estimated to be one year. 相似文献
8.
This paper examines sediment transport, sedimentation and properties of suspended matter and sediments in the Ra?a River estuary, a small, rock-bounded, microtidal, low-wave-energy karstic estuary in the north-eastern Adriatic. The Ra?a River is characterized by large variation in water flow and variable load of mineral particles. More than 90% of this load is brought into the estuary as fine-grained suspended matter, consisting of only 24–36% of carbonates, the rest being clays. Sedimentation occurs at the salt wedge, resulting in a prograding estuarine delta. Salt-induced flocculation is the predominant process of sediment deposition. The Ra?a estuary is infilling with sediment, and classifies as a disequilibrium estuary. We propose a modification of Cooper's (1993) classification scheme to include river-dominated, disequilibrium estuaries, with the Ra?a River as an example. 相似文献
9.
对于山区河流低坝而言,平时淤积在坝前的推移质粗沙可能会在洪水期集中翻越坝顶,形成高强度输沙。本文开展水槽试验,研究推移质粗沙自上游起动、推进、再翻越坝顶后向下游输移的过程,分析了输沙参数的变化特性及数理规律,描述了翻坝输沙模式及运动特征,揭示了输沙规律与河床形态之间的自然联系。取得如下认识:①输沙量随时间大致以幂函数规律增长。②低坝附近区域河床形态终将趋于稳定,上游和下游均形成相对稳定的曲面斜坡淤积体。③在不同的水流强度下推移质翻坝输移模式存在差异。对于一般水流强度工况,上游淤积体曲面斜坡表面泥沙颗粒以滚动或滑动模式起动,推移至接近坝顶位置时再跃移翻坝,后向下游输移;对于更高水流强度工况,后期的翻坝输沙模式可能发生显著转变,周期性边壁漩涡成为翻坝输沙的主要动力来源。 相似文献
10.
对于山区河流低坝而言，平时淤积在坝前的推移质粗沙可能会在洪水期集中翻越坝顶，形成高强度输沙。本文开展水槽试验，研究推移质粗沙自上游起动、推进、再翻越坝顶后向下游输移的过程，分析了输沙参数的变化特性及数理规律，描述了翻坝输沙模式及运动特征，揭示了输沙规律与河床形态之间的自然联系。取得如下认识：①输沙量随时间大致以幂函数规律增长。②低坝附近区域河床形态终将趋于稳定，上游和下游均形成相对稳定的曲面斜坡淤积体。③在不同的水流强度下推移质翻坝输移模式存在差异。对于一般水流强度工况，上游淤积体曲面斜坡表面泥沙颗粒以滚动或滑动模式起动，推移至接近坝顶位置时再跃移翻坝，后向下游输移；对于更高水流强度工况，后期的翻坝输沙模式可能发生显著转变，周期性边壁漩涡成为翻坝输沙的主要动力来源。 相似文献
11.
Samples of water and sediments were collected over a three year period from the entire region of Cauvery river basin excluding the estuary. On the basis of our observations, we have calculated the average composition of the Cauvery river at several locations from the catchment to the river mouth, the downstream profile of sediment load, annual erosion rates, solute and sediment fluxes and have predicted on long term changes. The sediment chemistry was determined by x-ray fluorescence (xrf) technique, and calculated mean compositions of the Cauvery and its tributary bed and the suspended sediment were compared to those of world average river sediments. Downstream profiles of some of the elements appear to be controlled by size and mineralogical characteristics besides local factors specific to the location of the samples. Interelemental relationships indicated good correlation among the transition elements indicating their co-genetic behaviour within the drainage basin. 相似文献
12.
The purpose of this paper is to analyze downstream effects of freshwater flow diversion from a small, active-continental-margin river basin. The Skokomish River delta is a tributary estuary to Hood Canal in Washington state that receives drainage from the southeastern side of the Olympic Mountains. Its drainage basin is steep, and rainfall is high. Approximately 40% of the annual average runoff of the entire system has been diverted from the North Fork Skokomish River for power production since completion of two dams in 1930; this water does not pass through the lower river or over the delta. Extensive logging has occurred in the remainder of the basin. Comparison of prediversion (1885) and postdiversion (1972) bathymetric surveys shows that deposition (about 0.013 to 0.022 m yr?1) has occurred on the inner delta and erosion (up to 0.033 m yr?1) on the outer delta. This steepening of the delta surface has apparently been caused by a loss of sediment transport capacity in the lower river and estuary combined with an increased sediment supply due to logging. Although the total area of unvegetated tidal flats thas decreased by only about 6%, there has been a more than 40% loss of highly productive low intertidal surface area. A conservative estimate of loss of eelgrass (Zostera marina) beds is 18%; a reduction in the size of mesohaline mixing zone has also occurred. These habitat losses are similar to those observed elsewhere in the world in larger river basins that have suffered water withdrawals of the same magnitude, but their impacts cannot either be evaluated or understood causally through consideration of simple measures like changes total estuarine deltaic area. Evaluation of estuarine effects of anthropogenic modification must, therefore, include consideration of both changes in habitat function and in the physical processes. These must be evaluated within the totality of the river basin-estuary system that cause these changes. In this case, sediment transport constitutes the critical link between fluvial alterations and the remote downstream, estuarine consequences thereof. 相似文献
13.
The flooding-drying process over the intertidal zone of the Satilla River estuary of Georgia was examined using a three-dimensional
(3-D) primitive equations numerical model with Mellor and Yamada's (1982) level 2.5 turbulent closure scheme. The model was
forced by the semi-diurnal M2, S2, and N2 tides and freshwater discharge at the upstream end of the estuary. The intertidal salt marsh was treated using a 3-D wet-dry
point treatment technique that was developed for the σ-coordinate transformation estuary model. Good agreement was found between
model-data comparison at anchor monitoring sites and also along the estuary that suggested that the model provided a reasonable
simulation of the temporal and spatial distribution of the 3-D tidal current and salinity in the Satilla River estuary. Numerical
experiments have shown that the flooding-drying process plays a key role in the simulation of tidal currents in the main river
channel and in water transport over the estuarine-salt marsh complex. Ignoring this process could lead to a 50% under-estimation
of the amplitude of tidal currents. The model results also revealed a complex spatial structure of the residual flow in the
main channel of the river, with characteristics of multiple eddy-like cell circulations. These complicated residual currents
are formed due to tidal rectification over variable topography with superimposition of inertial effects, asymmetry of tidal
currents, and baroclinic pressure gradients. Water exchanges over the estuary-intertidal salt marsh complex are asymmetric
across the estuary, and tend to vary periodically on the northern side while quickly washing out of the marsh zone on the
southern side. Strong Stokes’ drifting velocity was predicted in the estuary, so that the Lagrangian trajectories of particles
were characterized by strong nonlinear processes that differ significantly from those estimated by the Eulerian residual currents. 相似文献
14.
黄河是世界上含沙量最高的河流,其上游沙漠宽谷河段的冲沙输沙效应受来水来沙和地形条件变化等影响。为研究高含沙河流在低温条件下的输沙效应,通过引入水温因子,建立了黄河上游沙漠宽谷河段巴彦高勒站的输沙率模型。基于First Optimization平台的通用全局优化算法率定参数,验证了输沙率模型,量化了高含沙河流的低温输沙效应。结果表明:① 水温越低(1~7 ℃),河道输沙率越大,表明水温对河道输沙率的影响主要表现在低水温时期;② 任意一种工况下,水温1 ℃时河道输沙率约为25 ℃时的2.5倍;③ 低水温(5 ℃)较常温(16.6 ℃)下的河道输沙率提高了40.7%,在黄河上游开河低温期进行大流量冲沙输沙是水沙调控的最佳时机。研究成果以期为黄河上游沙漠宽谷河段低水温高效冲沙输沙和其他寒区高含沙河流的治理提供技术支撑。 相似文献
15.
黄河是世界上含沙量最高的河流,其上游沙漠宽谷河段的冲沙输沙效应受来水来沙和地形条件变化等影响。为研究高含沙河流在低温条件下的输沙效应,通过引入水温因子,建立了黄河上游沙漠宽谷河段巴彦高勒站的输沙率模型。基于First Optimization平台的通用全局优化算法率定参数,验证了输沙率模型,量化了高含沙河流的低温输沙效应。结果表明:①水温越低(1~7℃),河道输沙率越大,表明水温对河道输沙率的影响主要表现在低水温时期;②任意一种工况下,水温1℃时河道输沙率约为25℃时的2.5倍;③低水温(5℃)较常温(16.6℃)下的河道输沙率提高了40.7%,在黄河上游开河低温期进行大流量冲沙输沙是水沙调控的最佳时机。研究成果以期为黄河上游沙漠宽谷河段低水温高效冲沙输沙和其他寒区高含沙河流的治理提供技术支撑。 相似文献
16.
基于多沙河流"多来多排"输沙基本公式,建立了考虑上站来沙量、前期累计淤积量、临界输沙水量及干支流泥沙粒径影响的输沙量一般表达式。进而根据黄河内蒙古河段1953—2010年实测水沙资料,得到了内蒙古巴彦高勒—头道拐全河段及巴彦高勒—三湖河口和三湖河口—头道拐分河段的年输沙量公式,并根据输沙率法采用建立的输沙量公式计算了各河段1953—2010年的逐年冲淤量。选取三湖河口—头道拐河段的计算结果分析表明,在输沙基本公式基础上增加前期累计淤积量、临界输沙水量及干支流泥沙粒径参数,所得公式计算的年冲淤量与实测值之间的相关系数R2由基本公式的0.41依次提高到0.50、0.75和0.80,说明在基本公式基础上进一步考虑这些参数的必要性。此外,全河及分河段输沙公式计算所得输沙量及各河段冲淤量和累计淤积量与实测值的符合程度均较好,表明建立的输沙公式能够用于不同水沙条件下的输沙量和冲淤量计算,可为分析内蒙古河段的输沙特性和长期淤积趋势提供参考。 相似文献
17.
We present the large-scale simulation of watershed mass transport, including landslide, debris flow, and sediment transport. A case study of Tsengwen reservoir watershed under the extreme rainfall triggered by typhoon Morakot is conducted for verification. This approach starts with volume-area relation with landslide inventory method to predict temporal and regional landslide volume production and distribution. Then, debris flow model, Debris-2D, is applied to simulate the mass transport from hillslope to fluvial channel. Finally, a sediment transport model, NETSTARS, is used for hydraulic and sediment routing in river and reservoir. Near the water intake at the reservoir dam, the simulated sediment concentration is in good agreement with the measured one. The proposed approach gives good prediction and should help the management of reservoir operation and disaster prevention. 相似文献
18.
The influence of wind and river pulses on an estuarine turbidity maximum: Numerical studies and field observations in Chesapeake Bay 总被引：1，自引：0，他引：1
The effect of pulsed events on estuarine turbidity maxima (ETM) was investigated with the Princeton Ocean Model, a three-dimensional
hydrodynamic model. The theoretical model was adapted to a straight-channel estuary and enhanced with sediment transport,
erosion, deposition, and burial components. Wind and river pulse scenarios from the numerical model were compared to field
observations before and after river pulse and wind events in upper Chesapeake Bay. Numerical studies and field observations
demonstrated that the salt front and ETM had rapid and nonlinear responses to short-term pulses in river flow and wind. Although
increases and decreases in river flow caused down-estuary and up-estuary (respectively) movements of the salt front, the effect
of increased river flow was more pronounced than that of decreased river flow. Along-channel wind events also elicited non-linear
responses. The salt front moved in the opposite direction of wind stress, shifting up-estuary in response to down-estuary
winds and vice-versa.
Modeled pulsed events affected suspended sediment distributions by modifying the location of the salt front, near-bottom shear
stress, and the location of bottom sediment in relation to stratification within the salt front. Bottom sediment accumulated
near the convergent zone at the tip of the salt front, but lagged behind the rapid response of the salt front during wind
events. While increases in river flow and along-channel winds resulted in sediment transport down-estuary, only reductions
in river flow resulted in consistent up-estuary movement of bottom sediment. Model predictions suggest that wind and river
pulse events significantly influence salt front structure and circulation patterns, and have an important role in the transport
of sediment in upper estuaries. 相似文献
19.
Measurements show that in general salt is vertically well-mixed everywhere in the Great Bay Estuary, New Hampshire except near the river entrances at the head of the estuary. Dyer and Taylor’s (1973) modified version of Ketchum’s segmented tidal prism model has been applied to the Great Bay Estuarine System in order to predict high and low water salinity distribution for a specified river flow. The theory has been modified here to account for the mixing which occurs at the junction of two branches of an estuary. The mixing parameter, which in this model is related to the tidal excursion of water in the estuary, has been determined for different segments in the estuary on the basis of a comparison between predictions and a comprehensive data set obtained for a low river flow period. Using a mixing parameter distribution based on the low river flow calibration procedure the salinity distribution has been predicted for high river flow. The resulting salinity distribution compares favorably with observations for most of the estuary. The corresponding flushing times for water parcels entering at the head of the estuary during periods of low and high river flow is 54.5 and 45.9 tidal cycles respectively. 相似文献
20.
David H. Schoellhamer 《Estuaries and Coasts》2011,34(5):885-899
The quantity of suspended sediment in an estuary is regulated either by transport, where energy or time needed to suspend
sediment is limiting, or by supply, where the quantity of erodible sediment is limiting. This paper presents a hypothesis
that suspended-sediment concentration (SSC) in estuaries can suddenly decrease when the threshold from transport to supply
regulation is crossed as an erodible sediment pool is depleted. This study was motivated by a statistically significant 36%
step decrease in SSC in San Francisco Bay from water years 1991–1998 to 1999–2007. A quantitative conceptual model of an estuary
with an erodible sediment pool and transport or supply regulation of sediment transport is developed. Model results confirm
that, if the regulation threshold was crossed in 1999, SSC would decrease rapidly after water year 1999 as observed. Estuaries
with a similar history of a depositional sediment pulse followed by erosion may experience sudden clearing. 相似文献