长江中下游河道采砂对入海泥沙的影响

河道采砂可对河道的稳定性、航运安全、生态环境等造成重要影响。河道采砂可能会增加河流的输沙,也可能会减少河流的输沙。长江中下游河道的采砂量虽然很大,但却不是导致入海泥沙减少的主要原因,由河道采砂引起的河流输沙减少的相应比例应该不到采砂量的10%。汉口站和湖口站的来沙减少是造成大通站输沙减少的最主要原因。     

不同来源区洪水对黄河下游流量-含沙量关系的影响

根据1950-1960年及1974-1985年实测洪峰水沙资料,分析了不同来源区洪水对黄河下游花园口、高村、艾山、利津水文站流量 含沙量关系的影响,以河口镇至龙门区间、马莲河和北洛河总来水量占三门峡、黑石关、小董总水量的20%或25%以上作为中游粗沙来源区洪水,以河口镇至龙门区间、马莲河和北洛河总来水量占三门峡、黑石关、小董总水量的20%或25%以下作为细沙来源区或少沙区洪水。这样,黄河下游花园口、高村、艾山、利津水文站平均流量 平均含沙量关系可分为以增加平均含沙量为主和以增加平均流量为主的两个区。同时,河口镇至龙门区间、马莲河和北洛河的洪水,大大增加了黄河下游平均来沙系数和平均含沙量,并导致全下游河段的必然淤积。     

黄河下游凌情特征及变化

黄河下游冰情的基本特点和规律是:冬季有的年份封冻,有的年份不封冻;下游下段河道流凌封冻日期早,融冰、开河日期晚,封冻历时长,冰盖厚冰质坚;上段河道流凌封冻日期晚,融冰、开河日期早,封冻历时短,冰盖薄冰质酥。冰凌洪水特点是流量小,水位高且上涨快;凌峰流量自上而下沿程逐渐增大。近20年来,由于黄河下游河道水量大幅度减少,甚至发生连年断流,冬季气温持续偏高,加上水库调度等因素的共同影响,引起了凌情的相应变化。这些变化主要表现为:封开河日期提前,封河长度缩短、封冻冰量和槽蓄水量减少,冰塞冰坝发生次数减少,不封冻年频率增加等。     

Assessing sediment regime alteration of the upper Yangtze River

Employing the histogram matching approach, the sediment regime alteration of the upper Yangtze River was assessed and its possible causes and environmental influences were discussed. Daily sediment load and flow data from 1950 to 2008 were collected from Yichang hydrometric station. The annual sediment load series was segmented by heuristic segmentation algorithm in 1986 and 2003, and the multi-year mean values of the three phases were 5.28 × 10⁸, 3.89 × 10⁸ and 0.57 × 10⁸ t, respectively. One change point was found by cross wavelet transform in 2003 when the cross wavelet power became insignificant, which indicates the interruption of the common annual cycle of the sediment load and flow series. The sediment regime from 1986 to 2002 was altered by a total of 41 % compared with the regime from 1950 to 1985. It may be mainly attributed to numerous dams constructed in the tributaries, the Gezhouba Dam constructed in the mainstream, and land use and land cover change, e.g., the increased grassland with a coverage density larger than 50 %. The sediment regime alteration after 2003, assessed to be a total of 83 %, may be mainly attributed to the Three Gorges Reservoir. It breaks the natural process of sediment transport, reduces sediment concentration and releases clear water to the downstream which may result in some environmental problems, e.g., limited nutrients availability, river bed erosion, benthic habitat destruction, etc. The assessment of sediment regime alteration may provide some references for the environmental management and conservation of the Yangtze River.     

黄河下游河道输沙水量及计算方法研究

根据黄河下游1950年以来的水沙、河道冲淤及洪水观测资料,系统分析了黄河下游主要控制站输沙水量与来沙量、洪水量级、水沙搭配、区间引水引沙及河道允许淤积度等因子间的相互关系。在探讨泥沙输移规律和机理的基础上,引入水沙搭配参数,建立了适用于黄河下游主要控制站汛期及洪水期计算输沙水量的数学表达式,量化了水沙条件及河道允许淤积度变化对河道输沙水量的影响程度。该研究对维持黄河健康生命及黄河水资源的规划利用具有重要的理论和实际意义。     

Erosion balance in the watersheds of the western Paris Basin by high-frequency monitoring of discharge and suspended sediment in surface water

An accurate quantification of erosion, based on high-frequency monitoring of river discharge and suspended sediment fluxes is proposed for two watersheds in the western Paris Basin, a sensitive area with respect to erosion phenomena. This continuous monitoring makes it possible to include flood events of short duration, but significant erosion potential. The obtained erosion rate (16 and 21 t?km^?2?yr^?1) is among the weakest of the planet (3.5 to 18?000 t?km^?2?yr^?1). However, this annual balance does not reflect the behaviour of these rivers which can be torrential in certain cases. To cite this article: B. Laignel et al., C. R. Geoscience 338 (2006).     

Composition and mineralogy of suspended sediment in the fluvio-estuarine zone of the Loire River, France

The fluvio-tidal transition of suspended sediment in terms of mineralogy and composition in the Loire River drainage basin, the largest French river basin, was investigated in the fluvial zone at Montjean and in the tidal zone at Mauves-Thouaré, for a complete seasonal cycle. At Montjean, where the river experiences unidirectional flow, the composition and mineralogy (especially clays and clay minerals) of river suspended material (RSM) are governed by the river discharge, upstream contributions, climatic conditions and microbiological activities. However, due to reversing tidal and river currents at Thouaré, in the zone of tidal dynamics, these relations are changed. In the downstream direction sand and clay content in the RSM decrease while the silt content increases. Among clay minerals, between these two observation stations, montmorillonite remains constant, kaolinite diminishes, and the other minerals increase downstream. Combustible material (organic) and nitrate (NO₃) contents in the RSM increase whereas the phosphate (PO₄^3-) and CaCO₃ contents decline considerably during transport. At the head of the tidal zone, where the river flow encounters the tidal influence, there is a relatively stationary water mass (tidal slack) where sands, clays, phosphate, carbonate and silica are deposited by physical and chemical processes. Physical sedimentation takes place by simple gravitational deposition (sands), and by sorting and complicated differential settling (clays); chemical sedimentation takes place by precipitation (calcite-CaCO₃; apatite-Ca₅ (PO₄)³ (OH,F,Cl); coagulation of dissolved silica-SiO₂) in connection with seasonal algal bloom and eutrophic events.     

Controls of variation in suspended sediment concentration in the River Rother, West Sussex, England

Suspended sediment concentrations were determined for samples collected from the River Rother, West Sussex, and rating loops constructed for several hydrographs. The rating loops often exhibit hysteresis with a greater suspended sediment concentration for a given discharge occurring on the rising limb than on the falling limb. A comparison of these loops indicates that the hysteresis, and the suspended sediment concentration (for a given discharge) become progressively reduced when storm events occur in rapid succession. Various types of rating curves can be identified, and a model of suspended sediment concentration and discharge constructed. Controlling factors of suspended sediment concentration are river discharge, duration and frequency of the storm event, the length of time between successive events, and the time of year.     

The variation in suspended sediment and water properties in the flood-water front traversing the tidal flat

The initial flooding waters from twenty-four consecutive tides were examined for changes in water properties as the flood-front traversed the intertidal zone. The flood-front water temperature depended on the time of flooding as well as the sun’s insolation. On warm sunny days, the water temperature at the leading edge of the tide successively increased as the water flooded the tidal flat. In contrast, during cloudy days, and early morning and evening samplings, the flood-front water decreased during flooding. Flood-front water temperatures on warm days exceeded 34°C, some 15°C higher than the water observed in the deeper tidal channels. Flood-front salinities increased progressively across the intertidal zone regardless of local weather conditions, and were primarily controlled by mixing of surface waters with interstitial waters during the flooding process. Particulate matter concentrations were dependent on the interaction between small amplitude waves and varying intertidal bottom slope. Extreme variability in the particulate matter concentration across the tidal flat was in part caused by alternate resuspension and settling of fecal pellets composed of silty-clay aggregates which partly form the bottom sediment of the test area. The texture of the suspended particulate matter coarsens near shore, where wave resuspension became more effective on a steeper portion of the intertidal zone. *** DIRECT SUPPORT *** A01BY009 00003     

Effects of discharge of municipal waste on water quality of the lower Mississippi River

The effects of discharge of municipal wastes on water quality within the lower Mississippi River below Old River have been reevaluated using published water quality data in the Louisiana reach of the river for the water years 1974–1984. A novel graphical technique has facilitated the evaluation of upriver controls on water quality and the identification of sources and sinks along the lower Mississippi. Comparison of calculated annual fluxes at different downstream monitoring stations has simplified some of the problems inherent in evaluating analyses of samples collected from different water masses during a typical sampling run. The absolute concentrations of chloride, nitrite plus nitrate, total phosphorous, dissolved oxygen, BOD, and COD are all strongly dependent on processes occurring upriver. Nonpoint influx of materials from agricultural wastes and natural plant debris may be the dominant upstream sources of N, P, BOD, and COD. Increases in chloride and phosphorous downstream within the Lower Mississippi appear to be caused by discharge of industrial wastes. Nitrogen fluxes decrease downriver, except where there is local discharge of high-N, high-P industrial waste water, possibly from fertilizer plants. Removal of N and increases in BOD may be due in part to biological uptake. High river discharge rates and efficient, natural processes of reaeration maintain high oxygen saturation levels. With the exception of an increase in bacterial count, the discharge of municipal waste into the Mississippi River in Louisiana appears to have had no significant effect on water quality, a finding consistent with the earlier U.S. Geological Survey study of Wells (1980). It would be highly desirable for future mass balance studies if existing water quality programs on the Mississippi River were to adopt a Lagrangian sampling approach.     

Environmental changes after ecological water conveyance in the lower reaches of Heihe River,northwest China

This paper analyzed the dynamic change of the groundwater level by 6 years’ monitoring in field monitoring and the change of vegetation by the field survey and satellite remote sensing after watering in the lower reaches of Heihe River. The findings indicated: (1) the groundwater level elevation and the plant growth are closely related to the volume and the duration of watering. In general, groundwater level elevates dramatically and plants are growing much more vigorously after watering; (2) Watering incidence on groundwater keeps extending with the watering times increasing; (3) Plants grew rapidly in 100–400 m away from the water channel after watering. Watering incidence on vegetation reached 1,000 m; (4) In terms of the function and structure of ecosystem after watering in the lower reaches of Heihe River, the ecological water conveyance does not still reach the goal of ecological restoration at a large spatial scale at present. In addition, in order to solve fundamentally the problem of ecological environment worsens in the lower reaches of Heihe River, some suggestions and countermeasures are put forward.     

黄河下游输沙水量研究综述

对输沙水量的计算方法,黄河下游汛期、非汛期输沙水量的研究现状,水库对输沙水量的影响,输沙用水总量的研究现状等方面分别作了回顾。分析指出,输沙水量与来水含沙量、来水流量、河道冲淤、河床前期条件等有关。黄河下游各时期输沙水量不同,汛期最小,其余依次为非汛期、冬三月、凌汛期。水库调水调沙的同时也改变着黄河下游的输沙水量。利用水库群调水调沙,使小浪底水库以造床流量、高含沙水流输沙,是目前推荐的黄河下游节水减淤高效输沙入海的主要方式。提出了一些有待进一步研究的问题。     

黄河下游游荡段过流能力调整对水沙条件与断面形态的响应

河道过流能力与主槽形态有关，而主槽形态又取决于上游水沙条件，分析过流能力与这两者之间的关系对研究黄河下游游荡段河床演变规律有重要意义。从典型断面和河段平均两个尺度，定量分析了黄河下游游荡段1986—2015年平滩流量与水沙条件（来沙系数和水流冲刷强度）及汛前主槽形态（河相系数）之间的响应关系。结果表明：① 1986年至小浪底水库运行前，游荡段淤积严重，主槽萎缩，河道过流能力急剧下降，自小浪底水库运行后，游荡段发生强烈冲刷，其断面持续趋向窄深，过流能力逐年恢复；②建立了断面和河段平滩流量与水沙条件及河相系数的幂函数关系，二者相关系数均在0.5以上，但河段尺度相比于断面尺度的相关系数至少可提高17%；③河段平滩流量与前5年汛期平均水流冲刷强度及河相系数的相关系数接近0.94，相应计算公式能较好地反映平滩流量的变化过程，为分析其他河段平滩流量的变化提供了参考方法。     

黄河下游游荡段过流能力调整对水沙条件与断面形态的响应

河道过流能力与主槽形态有关,而主槽形态又取决于上游水沙条件,分析过流能力与这两者之间的关系对研究黄河下游游荡段河床演变规律有重要意义。从典型断面和河段平均两个尺度,定量分析了黄河下游游荡段1986-2015年平滩流量与水沙条件(来沙系数和水流冲刷强度)及汛前主槽形态(河相系数)之间的响应关系。结果表明:①1986年至小浪底水库运行前,游荡段淤积严重,主槽萎缩,河道过流能力急剧下降,自小浪底水库运行后,游荡段发生强烈冲刷,其断面持续趋向窄深,过流能力逐年恢复;②建立了断面和河段平滩流量与水沙条件及河相系数的幂函数关系,二者相关系数均在0.5以上,但河段尺度相比于断面尺度的相关系数至少可提高17%;③河段平滩流量与前5年汛期平均水流冲刷强度及河相系数的相关系数接近0.94,相应计算公式能较好地反映平滩流量的变化过程,为分析其他河段平滩流量的变化提供了参考方法。     

Assessing the impacts of climate and land use change on streamflow,water quality and suspended sediment in the Kor River Basin,Southwest of Iran

This research addressed the separate and combined impacts of climate and land use change on streamflow, suspended sediment and water quality in the Kor River Basin, Southwest of Iran, using (BASINS–WinHSPF) model. The model was calibrated and validated for hydrology, sediment and water quality for the period 2003–2012. The model was run under two climate changes, two land use changes and four combined change scenarios for near-future period (2020–2049). The results revealed that projected climate change impacts include an increase in streamflow (maximum increases of 52% under RCP 2.6 in December and 170% under RCP 8.5). Projected sediment concentrations under climate change scenarios showed a monthly average decrease of 10%. For land use change scenarios, agricultural development scenario indicated an opposite direction of changes in orthophosphate (increases in all months with an average increase of 6% under agricultural development scenario), leading to the conclusion that land use change is the dominant factor in nutrient concentration changes. Combined impacts results indicated that streamflows in late fall and winter months increased while in summer and early fall decreased. Suspended sediment and orthophosphate concentrations were decreased in all months except for increases in suspended sediment concentrations in September and October and orthophosphate concentrations in late winter and early spring due to the impact of land use change scenarios.     

Effect of changes in water level on sediment pore water redox geochemistry at a reservoir shoreline

Pore water samplers with high vertical resolution were used to evaluate the response of sediment redox geochemistry during transient hydrologic conditions at Lake Powell, a large reservoir in Utah and Arizona, USA. Samplers were deployed at two different yet proximal shoreline locations, White and Farley Canyons, before and after exposure of sediment to air and subsequent resubmersion, which resulted from fluctuations in the water level of the reservoir. Before exposure to air, an observed increase in dissolved Mn concentrations and, at Farley Canyon, an observed decrease in dissolved U concentrations across and immediately below the sediment–water interface indicated reducing conditions in the sub-surface. After exposure and resubmersion of the sediment, pore water profiles at each site differed distinctly from those observed before the fluctuation in water level. At White Canyon, an increase in U concentrations and a decrease in Mn concentrations in pore water after exposure and subsequent resubmersion are suggestive of oxidative processes occurring during the period of sediment exposure. Data from Farley Canyon suggest that the same processes may be occurring, but to a lesser extent. Depth profiles of As and Pb were also examined, but were relatively featureless compared to those of Mn and U. At both sites, sediment evaluated for pore water chemistry in the second sampling was only fully resubmerged for 2–5 days prior to the second sampling event, yet reducing conditions were clearly evident in the Mn pore water profiles. This suggests that the dynamics of the biogeochemical processes occurring in surface sediment at Lake Powell are responsive on the timescale defined by the fluctuating water levels in the reservoir.     

水库拦沙对长江水沙态势变化的影响

为探讨水库建设对水沙变化态势的影响,通过引入来沙系数、输沙模数和流域水库调控系数,深入分析了长江水库拦沙对水沙态势变异的作用。长江干支流水沙参数与流域水库库容参数之间有重要关系,主要水文站年输沙量随流域累积库容增加而逐渐减少,来沙系数和输沙模数随流域水库调控系数成指数关系衰减,表明水库蓄水拦沙是长江水沙态势变异的主要因素。长江干支流输沙量衰减规律有一定差异,支流来沙系数和输沙模数衰减规律相对独立,而干流上游站衰减幅度大于下游水文站,且干流各站输沙模数的衰减规律比较接近。     

A modeling study of the Satilla River estuary,Georgia. II: suspended sediment

A three-dimensional (3-D) suspended sediment model was coupled with a 3-D hydrodynamic numerical model and used to examine the spatial and temporal distribution of suspended sediments in the Satilla River estuary of Georgia. The hydrodynamic model was a modified ECOM-si model with inclusion of the flooding-drying cycle over intertidal salt marshes. The suspended sediment model consisted of a simple passive tracer equation with inclusion of sinking, resuspension, and sedimentation processes. The coupled model was driven by tidal forcing at the open boundary over the inner shelf of the South Atlantic Bight and real-time river discharge at the upstream end of the estuary, with a uniform initial distribution of total suspended sediment (TSS). The initial conditions for salinity were specified using observations taken along the estuary. The coupled model provided a reasonable simulation of both the spatial and temporal distributions of observed TSS concentration. Model-predicted TSS concentrations varied over a tidal cycle; they were highest at maximum flood and ebb tidal phases and lowest at slack tides. Model-guided process studies suggest that the spatial distribution of TSS concentration in the Satilla River estuary is controlled by a complex nonlinear physical process associated with the convergence and divergence of residual flow, a non-uniform along-estuary distribution of bottom stress, and the inertial effects of a curved shoreline.