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ＭＡＴＨＥＭＡＴＩＣＡＬＭＯＤＥＬＦＯＲＳＥＤＩＭＥＮＴＴＲＡＮＳＰＯＲＴＣＡＰＡＣＩＴＹＯＦＨＹＰＥＲＣＯＮＣＥＮＴＲＡＴＥＤＦＬＯＷＩＮＤＩＶＥＲＳＩＯＮＣＡＮＡＬＳ￥ＣＡＯＲｕｘｕａｎ；ＷＵＰｅｉａｎ；ＲＥＮＸｉａｏｆｅｎｇａｎｄＬＩＵＭｉｎｇ... 相似文献
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Modelling changes in suspended sediment from forest road surfaces in a coastal watershed of British Columbia 
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下载免费PDF全文 H. Andres Araujo Ashley Page Andrew B. Cooper Jeremy Venditti Erland MacIsaac Marwan A. Hassan Duncan Knowler 《水文研究》2014,28(18):4914-4927
Erosion from logging road surfaces, cut slopes, banks, and ditches represents a chronic source of sediment input to streams that can degrade aquatic habitats. Road surface erosion is of particular concern because the magnitude of sediment generation when traffic levels are high can be large. Current models for predicting sediment production from roads require information on area‐specific sediment delivery, which is not often available. Here, we developed a model to quantify suspended sediment concentrations (SSC) generated by forest roads surfaces under different conditions of use and density. This model is designed for a typical medium‐size coastal watershed of British Columbia or the American Pacific Northwest, and was applied to the Chilliwack River watershed as a case study. The results illustrate that intensive use of forest roads combined with high road density can increase the number of extreme sedimentation events over a predetermined threshold. A comparison of the effects of road density and the level of road use suggests that the level of road use is more important than the road density for the generation of fine sediment from road surfaces. However, the model omits the impact of roads on mass movements in a watershed, which represent a major source of sediment in steep watersheds, so the effect of road density is likely more substantial than the model predicts. The model is an attempt to overcome field data limitations by using an empirical relation between SSC and traffic variables, and presents a starting point for more intensive field studies that could be used to validate it. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Sediment incipient motion is a fundamental issue in sediment transport theory and engineering practice. Whilst Shields curve often is used to determine the threshold of sediment movement under unidirectional current conditions, it is unclear whether it can be directly applied for the wave or combined wave-current conditions. The study developed adaptive criterion curves describing incipient motion of sediment under wave and current conditions based on the flow pattern around the sediment particles. Firstly, the flow pattern law for fixed particles was recognized based on the friction law under various dynamic conditions (wave, current, and their combinations), and the flow pattern demarcations for incipient sediment motion were obtained with the threshold conditions for sediment movement under various dynamic conditions combined. Secondly, the exact shape of the Shields curve in each flow regime was derived under the current condition. By combining the flow pattern demarcations for incipient sediment motion under the wave condition, the criterion curve under the wave condition was derived. By combining the flow pattern demarcations for incipient sediment motion under the combined current-wave condition, the criterion curve for sediment incipient motion under the combined current-wave condition was derived. The results indicated that the flow pattern around incipient particles includes laminar, laminar-rough turbulent transition, and rough turbulent regimes. The criterion curves for sediment incipient motion under various dynamic conditions stayed the same in the laminar and rough turbulent regimes, but different in the transition regime. Depending on the relative strengths of the currents and waves, the shape of the criterion curve under the combined current-wave condition transitions adaptively between the criterion curve under the current condition and the criterion curve under the wave conditions. 相似文献
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HUANG Jinchi Senter Engineer Institute of Water Resources Hydropower Research Fuxing Road No. Beijing China WAN Zhaohui Professor Institute of Water Resources Hydropower Research Chegongzhuang West Road No. Beijing P.O.Box 《国际泥沙研究》1997,(3)
I.INTRODUCTIONTwo-dimensionalnumericalmodelisaPOwerfoltoolforengineersandriVermanagerstopredictfloodhydxaulics,identifyareasofinundation,anddesignoptionsforfloodcontrollingstructures.SomespecialproblemswithheavilysedimentladenflowriVershouldbecarefullyconsideredforthenumericalmodeldesigning;1.theplaneformofariVerisusuallybraidedanditsmainchannelshiftsoften.Themainchannelandbarreplaceeachotherseveraltimesinonefloodevent.Atagivenlocationthewaterdepthmaychangefromover10meterstoseveralcenhm… 相似文献
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The residual circulation over the continental slope, and in particular, its vertical structure, is analysed by means of an idealised hydrodynamic model. The model is based on the depth-dependent shallow-water equations under uniform along-isobath conditions and is forced by a prescribed meridional density gradient and tidal velocities. By means of expansion in the small Rossby number solutions are analysed for conditions representative for the continental slopes off the Hebrides and in the Bay of Biscay. The steady solution at zeroth order consists of a linear density-driven flow. At order a tidally rectified flow is found and a stationary flow due to self-interaction of the zeroth-order density-driven flow. At order 2 the leading-order effect of the interaction between the zeroth-order density-driven flow and the tides is found: the ‘interaction current’. The solutions up to and including order 2 constitute an along-isobath steady slope current which is comparable to field data. The slope current and the accompanying cross-shelf circulation depend strongly on the shelf and flow characteristics. For the Hebridean case the density forcing predominates, but for the Biscay case the tidal effects are of the same order of magnitude as the density effects. Under those conditions the interaction current is significant which implies that linear superposition of density and tidal effects differs from the non-linear combination of both. It is also shown that the depth-average of the interaction current differs essentially from the solution obtained from a depth-averaged model. 相似文献
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全球地表热流是反映地球内部热与动力学过程的一种主要能流.本文在三维球坐标框架下，就几个不同的粘度模型分别研究地幔内部密度异常(基于全球地震层析结果)以及板块运动激发的地幔流动的热效应及其对于观测地表热流产生和分布特征的贡献.由于地幔动力系统具有较高的Pe数，可以期望由板块运动激发的地幔流动将强烈地扰动地幔内部初始传导状态下的温度场以及地表热的热流分布.结果表明，与地幔内部密度异常产生的热效应相比，运动的板块及其激发的地幔流动在全球地表观测热流的产生和分布特征上起着更为重要的作用.观测到的大洋中脊处的高热流在很大程度上可以归因于板块激发的地幔流动的热效应.计算的平均温度剖面较好地揭示了岩石圈和D″层的温度特征，即温度随深度的剧烈变化，这与我们目前通过其他手段对岩石圈和D″层的温度结构了解是一致的.一个下地幔粘度比上地幔高出30倍的粘度结构(文中使用的粘度模型2)较之其余模型的拟合程度似乎更好. 相似文献
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Extensive field data of a density current driven by the differences in the cooling rates between the two lobes of a small lake are presented. These data illustrate the fact that this gravitational motion affects the whole system and dominates its lakewide circulation. Moreover, data are used to evaluate the entrainment into the density current and also to discuss the regime of the flow from a scaling analysis of the horizontal momentum equations. This analysis is specifically applied to the central area of the lake, where the density current flows from one lobe to the other. Results of this study show that in the longitudinal direction there is a balance between the pressure gradient and the turbulent viscous term. Further, it is found that geostrophy correctly describes the transversal pattern of the passage of the gravity current from the northern lobe to the southern, where it flows confined to the western shoreline. 相似文献
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Terrestrial laser scanning soil surfaces: a field methodology to examine soil surface roughness and overland flow hydraulics 总被引：1，自引：0，他引：1
Conventional roughness–resistance relationships developed for pipe and open‐channel flows cannot accurately describe shallow overland flows over natural rough surfaces. This paper develops a new field methodology combining terrestrial laser scanning (TLS) and overland flow simulation to provide a high‐resolution dataset of surface roughness and overland flow hydraulics as simulated on natural bare soil surfaces. This method permits a close examination of the factors controlling flow velocity and a re‐evaluation of the relationship between surface roughness and flow resistance. The aggregate effect of flow dynamics, infiltration and depression storage on retarding the passage of water over a surface is important where runoff‐generating areas are distant from well‐defined channels. Experiments to separate these effects show that this ‘effective resistance’ is dominated by surface roughness. Eight measurements of surface roughness are found to be related to flow resistance: standard deviation of elevations, inundation ratio, pit density (measured both perpendicular and parallel to the flow direction), slope, median depth, skewness of the depth distribution and frontal area. Hillslope position is found to affect the significant roughness measures. In contrast, infiltration rate has little effect on the velocity of water fronts advancing over the soil surfaces examined here and the effect of depression storage is limited. Overland flow resistance is depth dependent where complex microtopographic structures are progressively inundated. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Even with the flow of water over a soil surface in which roughness elements are well inundated, and in less erosive situations where erosional bed forms are not pronounced, the magnitude of resistance coefficients in equations such as those of Darcy–Weisbach, Chezy or Manning vary with flow velocity (at least). Using both original laboratory and field data, and data from the literature, the paper examines this question of the apparent variation of resistance coefficients in relation to flow velocity, even in the absence of interaction between hydraulics and resulting erosional bed forms. Resistance equations are first assessed as to their ability to describe overland flow velocity when tested against these data sources. The result is that Manning's equation received stronger support than the Darcy–Weisbach or Chezy equations, though all equations were useful. The second question addressed is how best to estimate velocity of overland flow from measurements of slope and unit discharge, recognizing that the apparent flow velocity variation in resistance coefficients is probably a result of shortcomings in all of the listed resistance equations. A new methodology is illustrated which gives good agreement between estimated and measured flow velocity for both well-inundated sheet and rill flow. Comments are given on the predictive use of this methodology. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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Shang Xu YingMin Wang XueChao Peng HuaYao Zou Yan Qiu ChengLin Gong HaiTeng Zhuo 《中国科学:地球科学(英文版)》2014,57(11):2769-2780
The continental slope of the Taiwan Shoal, which has cultivated numerous submarine canyons, is located in a passive continental margin environment. However, the trend of the Taiwan Canyon, with its 45° intersection angle, is obviously different from that of the erosion valley downward along the continental slope. A distinct break is present in the lower segment of the Taiwan Canyon, which then extends from west to east parallel to the continental slope until finally joining the Manila Trench. By utilizing multiple-beam water depth data, high-resolution seismic data, and sediment cores, this study describes the topographic characteristics of the Taiwan Canyon and provides a preliminary discussion on the origin of the Taiwan Canyon and its effect on deepwater sediment. The terrain, landform, and sediment of the Taiwan Canyon exhibit segmentation characteristics. The upper segment is characterized primarily by erosion, downward cutting with a V shape, and wide development of sliding, slumping, and other gravity flow types. The middle segment is characterized mostly by U-shaped erosion-sedimentation transition and development of an inner levee. The lower segment is characterized primarily by sedimentation and development of a sediment wave. The bottom current has a significant reworking effect on the interior sediments of the canyon and forms reworked sands. The formation and evolution of the Taiwan Canyon is closely related to sediment supply, gravity sliding(slumping), faulting activities, and submarine impaling. Given the sufficient terrigenous clastic supply, the sediments along the continental shelf edge continuously proceed seaward; gliding and slumping in the front edge provide driving forces for the formation of the canyon. Faulting activities result in stratum crushing, and the gravity flow takes priority in eroding the relatively fragile stratum. Thus, the direction of the extension of the canyon crosses the surrounding erosion valley obliquely. Seamounts are formed through submarine impaling. Owing to seamount blocking, the lower segment of the canyon is turned toward the east–west direction. Large amounts of sediments overflow at the turning, forming sediment waves. 相似文献
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ＴＨＥＴＨＥＯＲＥＴＩＣＡＬＳＴＵＤＹＯＮＴＨＥＬＡＷＳＯＦＤＲＡＧＲＥＤＵＣＴＩＯＮＢＹＡＥＲＡＴＩＯＮＩＮＯＰＥＮＣＨＡＮＮＥＬ１ＺＨＥＮＧＹｏｎｇｇａｎｇ２,ＦＡＮＧＤｕｏ３ａｎｄＬＩＧｕｉｆｅｎ４ＡＢＳＴＲＡＣＴＴｈｅｌａｗｓｏｆｄｒａｇｒｅ... 相似文献
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This paper deals with the saltation of bed-load solid grains in flowing water. Experiments have been carried out by means of high-speed photographing and advanced data processing techniques while the analysis is made by combined method of mechani- cal and statistical theories. Experiments reveal that saltation is the main form of the bed-load transport under ordinary flow conditions. Taking successive saltation as the model of bed-load transport, systematic analysis has been made with regard to the forces acting on grains and the variation of their magnitudes along the saltation trajec- tories to obtain the kinematic and dynamic properties of these grains. The statistical analysis shows that the probability density functions of the relative height and length of saltation are in conformity with distribution, while the probability density functions of the relative velocities of saltation are in conformity with the Gaussian distribution. 相似文献
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Matteo Tregnaghi Andrea Marion Andrea Bottacin‐Busolin Simon J. Tait 《地球表面变化过程与地形》2011,36(13):1761-1769
In this paper a modelling approach is presented to predict local scour under time varying flow conditions. The approach is validated using experimental data of unsteady scour at bed sills. The model is based on a number of hypotheses concerning the characteristics of the flow hydrograph, the temporal evolution of the scour and the geometry of the scour hole. A key assumption is that, at any time, the scour depth evolves at the same rate as in an equivalent steady flow. The assumption is supported by existing evidence of geometrical affinity and similarity of scour holes formed under different steady hydraulic conditions. Experimental data are presented that show the scour hole development downstream of bed sills due to flood hydrographs follow a predictable pattern. Numerical simulations are performed with the same input parameters used in the experimental tests but with no post‐simulation calibration. Comparison between the experimental and model results indicates good correspondence, especially in the rising limb of the flow hydrograph. This suggests that the underlying assumptions used in the modelling approach are appropriate. In principle, the approach is general and can be applied to a wide range of environments (e.g. bed sills, step‐pool systems) in which scouring at rapid bed elevation changes caused by time varying flows occurs, provided appropriate scaling information is available, and the scour response to steady flow conditions can be estimated. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Sediment data were analyzed to determine grain‐size dependant factors affecting sediment transport in a low‐ordered, ephemeral watershed. Sediment and flow samples were collected during 22 flow events at the outlet of a 4·53 ha sub‐watershed within the Walnut Gulch Experimental Watershed in south‐eastern Arizona. Measured concentrations ranged from 4191 to 115 045 mg l?1 and included grain sizes up to 8·0 mm in diameter. Two grain‐size dependent transport patterns were observed, that of the finer grain‐size fraction (approximately < 0·25 mm) and that of a coarser grain‐size fraction (approximately ≥ 0·25 mm). The concentration of the fine fraction decreased with flow duration, peaking near the beginning of a flow event and declining thereafter. The concentration of the fine fraction showed slight trends with season and recovery period. The concentration of the coarse fraction displayed a slight negative trend with instantaneous discharge and was not correlated with event duration. These patterns typically produced a condition where the majority of the fine fraction of the sediment yield was evacuated out of the watershed before the hydrograph peak while the majority of the coarser sediment was evacuated during the falling limb of the hydrograph. Each grain‐size dependent transport pattern was likely influenced by the source of the associated sediment. At the flow event time scale, the fines were primarily wash load, supplied from the hillslopes and the coarser grains were entrained from the channel bed. Because transport patterns differ based on grain size, attempts to define the total sediment concentration and sediment yield by the behavior of a single grain‐size fraction may lead to erroneous results, especially when a large range of sediment grain sizes are present. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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1 RESISTANCE TO WATER-STONE FLOW As a special sort of debris flow, water-stone flow, or as generally called, sub-viscous debris flow, always occurs in channel of steep slope, dominantly in composition of coarse grains of bedload and laminated load with less suspended load. In some literature, water-stone flow is defined for convenience of study as that without suspended fine grains in composition, and it follows from this definition that transportation concentration of this kind of … 相似文献
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Abstract Laboratory flume experiments were undertaken to measure the vertical profiles of mean flow velocity for three different flow discharges and four different stem densities of Hydrilla verticillata. The data were used to calculate three parameters, namely Manning's roughness coefficient, the Reynolds number and the Froude number. In addition, empirical equations were obtained for the vertical distribution of measured flow velocity within the transitional zone and above the plant canopy. The results show that: (a) the vertical distribution of measured flow velocity exhibits three zone profiles; (b) Manning's roughness coefficient decreases with increasing depth-averaged flow velocity; (c) the relationship between Manning's roughness coefficient and the depth-averaged flow velocity is within the smooth left inverse curve; (d) Manning's roughness coefficient significantly changes with increasing density of Hydrilla; (e) the Froude number is independent of the density of Hydrilla; and (f) both the Reynolds number and the Froude number increase with increasing depth-averaged flow velocity. Citation Shi, J.Z., Li, Y.-H., Hughes, J.M.R., and Zhao, M., 2013. Hydrological characteristics of vegetated river flows: a laboratory flume study. Hydrological Sciences Journal, 58 (5), 1047–1058. Editor Z.W. Kundzewicz 相似文献
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Nicholas J. Clifford 《地球表面变化过程与地形》1998,23(2):109-127
This paper compares flow intensity data obtained with different instruments from a variety of fluvial environments. It examines associations between the root-mean-square of longitudinal velocity fluctuations (flow intensity), local mean velocity, relative depth, and boundary resistance. Results indicate systematic differences in the behaviour of flow intensity which scale with respect to position in the boundary layer (deep sand-bedded rivers), boundary grain resistance (shallow river environments with coarse beds), and possibly form resistance (shallower sand-bedded rivers). Preliminary approaches to prediction and modelling of variations in flow intensity are suggested based upon linear regression relationships. Intensity values are also compared with theoretical and empirical limits to the use of Taylor's substitution, which allows time and frequency properties of a single-point velocity time series to be used to yield a flow length scale. In general, limits are exceeded in all environments for near-boundary flow measurements, but are met for y/d > 0·3 in most cases in sand-bed rivers, and for y/d > 0·4 in some gravel-bed environments. © 1998 John Wiley & Sons, Ltd. 相似文献