河流潜流带渗透系数变化研究进展

介绍了河流潜流带的含义,即是河水与地下水发生物质能量交换的区域,其水力联系和交换水量大小受河床沉积物渗透系数的影响。对近年来国内外学者对河床潜流带渗透系数变化进行了大量研究。由于特殊的环境与水文地质条件,潜流带渗透系数的大小不仅取决于沉积物孔隙大小和孔隙的连通性,而且与生物扰动、河流流水等作用紧密相关:洪水带来的细小颗粒引起河床表面沉积物孔隙淤塞,致使渗透系数减小,但在洪水退后,潜流带的水文交换和生物扰动能破坏淤塞层,从而引起反淤塞作用,造成河床渗透系数增大。因此,淤塞-反淤塞作用改变着河床的渗透性能。最后,指出存在的问题今后的研究方向。     

Estimation of Sediment Hydraulic Conductivity in River Reaches and its Potential Use to Evaluate Streambed Clogging

Streambed substrates have pervasive effects on stream biodiversity and biogeochemistry. The excessive input of fine sediments in streams and the subsequent alteration of the physical characteristics of streambed substrates are considered today as a major environmental issue. The estimation of streambed hydraulic conductivity (K) may be simpler than other estimations of reach‐scale physical characteristics and could serve to quantify the alterations of streambeds across stream networks. In this study, we examined between‐reach and within‐reach variability and temporal changes of streambed K across 101 stream reaches in France, including nine reaches previously judged as clogged and nine as references (unclogged). We also examined the relationships between K and some environmental variables such as vertical hydraulic gradient, streambed grain size, flow velocity or distance to the bank. We demonstrated that 15 measurements of streambed K per reach could be used to compare streams among each other and over time. Clogged reaches displayed much lower K than reference reaches, and more generally, reach‐averaged K and the number of non‐null K values per reach allowed discriminating reaches among each other without observer bias. K was higher in upwelling compared with downwelling areas, probably because of fine sediment uplifting. With the low cost in terms of equipment (<€100 per unit) and time (2–4 h per site), reach‐scale streambed K estimates are promising for studying the alterations of streambed substrates across stream monitoring networks such as clogging, but also for understanding large‐scale drivers of these alterations, or for upscaling recent developments in hyporheic ecology at the reach scale. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of bed geometric characteristics on hyporheic exchange

As an active ecotone between the surface stream and groundwater, hyporheic zone (HZ) plays a crucial role in hydrological and ecological processes. Previous numerical simulation and experimental studies have shown that hyporheic exchange can be affected not only by current but also by geometric characteristics of the streambed. However, the geometric characteristics that affect hyporheic exchange remain unclear. In this study, a one-way sequential coupling method was established to connect the river water flow and pore-water flow in the streambed. The change of flux at the interface, mass flux, depth, and area of hyporheic zone were investigated by altering the bed geometric characteristics, i.e. the depth, crest position, and shapes of bedforms. The results clearly demonstrate the following conclusions: (a) the hyporheic exchange flux, depth and area with wave-like bedform is greater than the triangular bedform. (b) The increase of the bed height accelerates the hyporheic exchange processes at the sediment–water interface. (c) A good linear relationship was found between the depth and area of the hyporheic zone. These results provide necessary theoretical understandings of hyporheic exchange, broadening the knowledge of mechanism of stream-streambed exchange processes.     

A multi-parameter approach to quantify riverbed clogging and vertical hyporheic connectivity

Riverbed clogging is key to assessing vertical connectivity in the hyporheic zone and is often quantified using single-parameter or qualitative approaches. However, clogging is driven by multiple, interacting physical and bio-geochemical parameters, which do not allow for a conclusive assessment of hyporheic connectivity with single-parameter approaches. In addition, existing qualitative assessments lack transparency and repeatability. This study introduces a Multi-Parameter Approach to quantify Clogging and vertical hyporheic connectivity (MultiPAC), which builds on standardized measurements of physical (grain size characteristics, porosity, hydraulic conductivity) and bio-geochemical (interstitial dissolved oxygen) parameters. We apply MultiPAC at three gravel-bed rivers and show how the set of parameters provides a representative appreciation of physical riverbed clogging, thus quantifying vertical hyporheic connectivity. However, more parameters are required to fully characterize biological clogging. In addition, MultiPAC locates clogged layers in the hyporheic zone through multi-parameter vertical profiles over the riverbed depth. The discussion outlines the relevance of MultiPAC to guide field surveys.     

雨洪水回灌过程中堵塞滤层特征试验

采用室内砂柱试验模拟雨洪水回灌条件下含水层的堵塞过程,通过测定堵塞层的渗透系数和渗滤速率的变化分析回灌过程中的物理堵塞特征。试验结果显示,在回灌后36h,砂柱上部(25～40cm)的渗透系数明显减小,由初始的6.58m/d减小到3.72m/d,而中下部(40～70cm)的渗透系数变化很小,由初始的6.45m/d减小到5.25m/d;比较悬浮物质量浓度分别为50mg/L,100mg/L,200mg/L和400mg/L的回灌水回灌过程表明,悬浮物质量浓度越高,砂层的渗透速率下降越快;对比分析回灌前后的悬浮物颗分结果表明,回灌后的悬浮物(砂层表部淤泥层)出现细化现象;回灌过程中在砂柱表面形成的淤泥层和砂层上部的淤堵是整个含水层堵塞失效的主要原因。     

螃蟹扰动作用对滨海湿地水盐交换的影响

为探究生物扰动作用对滨海湿地物质交换的影响,以螃蟹为研究对象进行室内控制试验,模拟了潮汐条件下不同螃蟹密度时沉积物地貌变化和水盐运移情况。结果表明:螃蟹能够将大量地下沉积物搬运至地表,形成起伏多变的微地形,使沉积物表面积明显增大;螃蟹活动能促进地表水与地下水交换,加快浅层土壤的盐分运移过程;地表水与地下水交换量和盐分运移量均随螃蟹密度的增大而明显增大。生物扰动作用是造成沉积物地貌改变的重要因素,进而促进了滨海湿地的水盐交换。     

On the process of fine sediment infiltration into static gravel bed: A CFD–DEM modelling perspective

The gravel bed clogging, caused by infiltration and accumulation of fine sediment, degrades the river ecology. A proper understanding of the infiltration process, and underlying mechanism and causes, are necessary to take preventive measures. The process of fine sediment infiltration into static gravel bed is studied by distinguishing between bridging and percolation behaviours, as they affect the river ecology and physical processes occurring in the river system differently. However, several contradicting observations, concerning their occurrences, are reported. We employed the unresolved CFD–DEM method to simulate and investigate the infiltration process. The theoretical size ratios, corresponding to different geometrical configurations for a binary mixture of mono-disperse spherical particles, representing bridging and percolation processes, are considered and simulated with and without flowing water effects. The effects of several turbulence models on the infiltration process are also studied. We found that fine sediment infiltration in fluvial deposits is mainly gravity-dominated, supporting Cui's hypothesis that fine sediment infiltration through intra-gravel flow is similar to fine sediment infiltration driven by gravity. In contrast to consensus in the field, our results demonstrate that the occurrences of different infiltration processes (bridging and percolation) seem to be independent of gravel bed thickness, rather depend only on the relative grain size distribution of fine sediment and gravel. However, a precise definition of a ‘thick enough’ gravel bed is necessary to distinguish between bridging and percolation behaviours. Here, we hypothesize a suitable gravel bed thickness, which might be regarded as a ‘thick enough’ gravel bed.     

Flume simulations of salmon bioturbation effects on critical shear stress and bedload transport in rivers

Nest (redd) construction by female salmonids involves sequences of pit excavation and filling that winnow fines, loosen grains, and moves sediment downstream into a tailspill mound shaped like a dune. Prior research suggests that such bioturbation may destabilize streambeds by reducing friction between grains and converging flow that elevates shear stress on tailspills. Bed stability may alternatively be enhanced by form drag from redds that lowers basal shear stress, an effect that varies with the proportion of the bed that is occupied by redds (P). I used simulated redds and water‐worked (“unspawned”) beds in a laboratory flume to evaluate these competing influences on critical conditions and bedload transport in experiments with P = 0.11 (1 redd), 0.29 (2 redds), and 0.38 (3 redds). Results from competence (largest grain) and reference transport rate estimates of Shields stress indicate that particle entrainment inversely related to P. Bedload transport rates also increased as exponential functions of P and the boundary shear stress that exceeded critical conditions. Therefore, redd form drag did not overcome the destabilizing effects of redd construction. Instead, grain mobility and bedload transport increased with P because larger bed areas were composed of relatively loose grains and redd topography that experiences elevated shear stresses, as suggested in prior research. By winnowing fines and increasing bed surface mobility that exposes small particles in subsurface areas to flow, bioturbation by salmon can mitigate fine sedimentation of streambeds, which suggests an active role for salmon in restoring fish habitat in streams.     

ON THE IMPORTANCE OF CONSIDERING CHANNEL MICROFORMS IN GROUNDWATER MODELS OF HYPORHEIC EXCHANGE

The infiltration of stream water in the sediment and its return to the stream—a process known here as hyporheic exchange flows (HEF)—is a critical control of the structure and functions of the stream ecosystem. River restoration programmes will increasingly require quantitative methods for evaluating this influence. Previous studies have already shown the potential of numerical groundwater models to characterize HEF and compare restoration scenarios. Although various sources of uncertainty are acknowledged, the potential effect of small streambed structures (or microforms), such as grains or ripples, embedded in channel‐unit scale structures (or macroforms), such as riffle‐pool sequences, is commonly ignored. Here, a simple conceptualization through a 2‐D vertical model is used to test whether (i) ignoring microforms in groundwater models at the macroform scale can impact estimations of residence times; (ii) microforms can influence HEF patterns driven by macroforms; and conversely (iii) the uncertainty of head measurements in stream piezometers can affect our understanding of HEF patterns. Results show that (i) residence times and flux estimations can be strongly affected by the modeller's choice to represent microform‐induced HEF or not; (ii) the interaction of the microform and macroform scales can induce various subsurface flow patterns; and (iii) the perceived significance of microform‐induced HEF is highly sensitive to the uncertainty of in‐stream measurements of subsurface heads. Little is known about the relative efficiency of these microform and macroform scales, which are effectively influencing exchange at different depths and interacting with each other. Future studies that consider biogeochemical cycling or streambed ecology should be placed in this context. It is also necessary to find ways of including this source of uncertainty in groundwater models of HEF. Copyright © 2012 John Wiley & Sons, Ltd.     

破碎波作用下粉沙悬移质浓度垂向分布的实验研究

通过水槽实验对破碎波作用下驴驹河粉沙和黄骅粉沙悬沙浓度的沿程分布和垂向分布进行了研究,并对实验现象进行了初步分析。实验中发现:在波浪破碎前近底有高浓度含沙水体层,而在波浪破碎后高浓度含沙水体层消失;断面平均悬沙浓度在破碎点附近达到最大,在破碎点前,断面平均悬沙浓度沿程增大,而在破碎点后,断面平均悬沙浓度沿程减小;在波浪破碎前附近,上层水体紊动较强,从而悬起比平坡情况下更多的泥沙,使悬沙浓度不但在下层水体高,而且在上层水体也较高,因此在计算泥沙输移时,应对此更加注重。     

悬浮泥沙沿程淤积

研究床沙不起悬但存在紊动条件下的悬浮泥沙沿程淤积,这种淤积常发生在水库、沉沙池等较深水体中。研究发现试验水槽中悬浮泥沙淤积依沿程可划分为三个区段:射流区、悬沙超饱和区、悬沙缓淤区,三个区段的悬沙浓度剖面与淤积量沿程变化有显著不同,在分析沿程淤积公式时应采用悬沙超饱和区的试验数据。本文从理论与试验资料角度,详细讨论悬沙沿程淤积的公式,并建议采用JobsonandSayre(1970)提出的公式计算悬浮泥沙沿程淤积。     

特高混凝土面板堆石坝排水体局部缺陷排水量影响研究

针对我国在建的某特高混凝土面板堆石坝,研究其长期服役过程中排水体发生局部变形、淤堵等缺陷对排水能力的影响.研究结果表明:水平排水体局部沉降变形高度、淤堵范围与排水量呈负相关关系,且局部沉降高度小于排水体厚度时,对坝体浸润线和排水体排水量影响较小;水平排水体局部淤堵时,由于阻渗作用,在排水体淤堵断面前坝体浸润线高度明显升...     

INFLUENCE OF ENVIRONMENTAL INSTABILITY OF GROUNDWATER‐FED STREAMS ON HYPORHEIC FAUNA,ON A GLACIAL FLOODPLAIN,DENALI NATIONAL PARK,ALASKA

Macroinvertebrate community distributions were investigated within the benthic and hyporheic zone of five groundwater‐fed streams, on a floodplain terrace, in a glacierized catchment in Alaska, in summer 2008. The streams were characterized by a distinct gradient in environmental instability and provided an opportunity to determine whether the local variability in environmental instability of groundwater‐fed streams (reflecting differences in lengths of groundwater flow pathways) are of sufficient magnitude and frequency to influence macroinvertebrate community distribution. Individual measures of surface‐water temperature, streamflow, streambed stability and sediment size were incorporated into a multivariate index of environmental instability (IEI), using principal components analysis. In the hyporheic zone, a logarithmic association was observed between macroinvertebrate diversity and IEI and a quadratic association between abundance and IEI. The increase in diversity along the gradient of instability reflected a greater evenness of taxa caused by reduction in abundance of Chironomidae, combined with an increase in abundance of several less dominant taxa (Limnephilidae, Empididae, Baetidae and Simuliidae). At the surface, a quadratic association between diversity and IEI was observed, consistent with the intermediate disturbance hypothesis. Chironomidae, Nemouridae and Empididae presented contrasting surface and hyporheic distributions, indicating use of the hyporheic zone as a refuge. Moreover, covariance in the surface and hyporheic distribution of Limnephilidae and Chloroperlidae suggested the use of the hyporheic zone as an extension of the benthic habitat. The data indicate that local variability in environmental conditions between groundwater‐fed streams is sufficient to induce differences in macroinvertebrate communities and in the response of individual taxa. Copyright © 2012 John Wiley & Sons, Ltd.     

Bankfull shear velocity predicts embeddedness and silt cover in gravel streambeds

Excess fine sediment (<2 mm) deposition on gravel streambeds can degrade habitat quality for stream biota. Two measures of fine sediment deposition include embeddedness and silt cover (<62.5 μm). Embeddedness measures fine sediment in interstitial pore spaces, whereas silt cover, primarily deposited during low flows, measures fine sediment draped on the streambed's surface. Here, we demonstrate that a baseline level of embeddedness and a maximum value of silt cover can be predicted from bankfull shear velocity, which can be estimated from river channel and streamflow characteristics, independently of knowing the sediment supply. We derive an equation for bankfull shear velocity that only requires knowing bankfull flow, channel width, and channel slope, which can be readily obtained in the United States from freely available, remotely sensed data. We apply this methodology to data collected at 30 sites in the Piedmont region of Virginia and North Carolina. This work is an important step in developing statistical models of stream ecosystems in which geophysical variables can predict embeddedness and silt cover, which commonly limit biotic assemblages.     

Hyporheic invertebrate community composition in streams of varying salinity in south‐western Australia: diversity peaks at intermediate thresholds

Many streams of southwestern Australia have become secondarily saline through land clearance and other human activities in their catchments. Elevated salinities impact on aquatic biota and ecological processes of surface streams but little is known of the effects on the diversity and community composition of hyporheic (subsurface) invertebrates occupying the saturated sediments where surface and groundwaters exchange. We hypothesized that biodiversity of hyporheic invertebrates would decline with increasing salinity, especially where saline groundwater upwelled into the surface stream. We also predicted changes in community composition associated with salinity and direction of vertical hydrological exchange. Water and hyporheic invertebrates were sampled from downwelling and upwelling zones of 13 streams in southwestern Australia ranging in median surface water salinity from 0.27 to 17.86 g L⁻¹. Overall, taxa richness of hyporheic invertebrates was uncorrelated with salinity but, surprisingly, correlated positively with the salinity of upwelling water. However, when the sites were divided into ‘fresh’ (<3 g L⁻¹) and ‘mesosaline’ (>3 g L⁻¹) groups, this relationship became non‐significant. Instead, taxa richness and total abundance were correlated positively with salinity of downwelling water in fresh sites and negatively in mesosaline sites, resulting in a peak in richness at intermediate salinities. Community composition was unrelated to direction of hydrological exchange but was strongly associated with hyporheic salinity. Hyporheic assemblages of ‘fresh’ rivers were typified by harpacticoid copepods and candoniid ostracods, whereas the amphipod Austrochiltonia and several dipteran groups were more common below ‘mesosaline’ rivers. Although many hyporheic taxa collected in this study apparently have broad tolerances to salinity, secondary salinization due to human activities potentially changed community composition, possibly altering rates of ecological processes such as organic matter breakdown occurring within the sediments of streams undergoing salinization. Copyright © 2007 John Wiley & Sons, Ltd.     

粗化床面非均匀沙推移质运动扩散特性研究

对泥沙颗粒运动规律的把握是准确估算推移质输沙率的基础.本文开展了粗化床面条件下的水槽试验,分析了非均匀沙颗粒的均方位移和速度自相关系数变化,并与已有均匀沙试验进行了对比.结果表明,粗化床面存在着由单个或多个粗颗粒组成的粗化结构体,形成比平整床面更复杂的底部边界,粗化结构体对泥沙颗粒运动造成较大影响,颗粒在运动过程中与水...     

化学淤堵作用下尾矿砂孔隙分布及渗透特性试验研究

对石板沟尾矿库调研采样,分析尾矿砂表面化学元素并确定钙离子为造成该库化学淤堵的主要元素.添加氯化钙溶液改变尾矿砂中的钙离子含量,采用渗流试验装置及核磁系统观测不同溶液浓度和水力梯度作用下尾矿砂孔隙分布、孔隙率和渗透系数的时序变化规律,分析其影响因素.结果表明:核磁共振系统能准确地获得尾矿砂在不同条件下的孔隙率和孔隙分布...     

水库坝前冲刷漏斗平衡形态的数学模拟

应用作者提出的水沙两相流立面二维数学模型和基于算子分裂的数值计算方法,对水库坝前冲刷漏斗平衡形态及相应水、沙流动特性进行数学模拟。分析表明:在邻近孔口的局部范围内,漏斗平衡形态直接依赖于孔口的布置形式与调度运行;对于孔口影响域以外的区域,则主要取决于上游来水、来沙条件。对黄河小浪底水库和三门峡水库在概化条件下的实例计算结果与现有观测成果和预测分析基本符合,对工程实际有一定参考价值。     

河流泥沙模型输沙计算中对泥沙级配的考虑

现有的水槽试验资料及天然河流实测资料表明，在水流输沙计算中考虑泥沙级配对水流挟沙力的影响，能够深入地把握水流挟沙的力学机制，进而提高输沙计算的精度。     

水流作用下的悬沙垂向扩散系数

利用华东师范大学河口海岸学国家重点实验室的波-流-泥沙变坡水槽,进行系列二维均匀流平衡输沙情况下悬沙扩散特性研究实验.根据实验数据,计算不同水流情况下的悬沙浓度垂向分布,确定悬沙垂向扩散系数及它的垂向分布.所得结果表明悬沙垂向扩散系数与水流扩散系数成正比,其比例系数正比例于摩阻流速;悬沙扩散系数的垂向分布可用抛物线来描述.