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1.
The particle size of the bed sediments in or on many natural streams, alluvial fans, laboratory flumes, irrigation canals and mine waste deltas varies exponentially with distance along the stream. A plot of the available worldwide exponential bed particle size diminution coefficient data against stream length is presented which shows that all the data lie within a single narrow band extending over virtually the whole range of stream lengths and bed sediment particle sizes found on Earth. This correlation applies to both natural and artificial flows with both sand and gravel beds, irrespective of either the solids concentration or whether normal or reverse sorting occurs. This strongly suggests that there are common mechanisms underlying the exponential diminution of bed particles in subaerial aqueous flows of all kinds. Thus existing models of sorting and abrasion applicable to some such flows may be applicable to others. A comparison of exponential laboratory abrasion and field diminution coefficients suggests that abrasion is unlikely to be significant in gravel and sand bed streams shorter than about 10 km to 100 km, and about 500 km, respectively. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
2.
ABSTRACT An infiltration model based on the Green-Ampt assumptions is developed for a class of non-uniform soils in which saturated hydraulic conductivity decreases as an exponential function of depth, and the storage-suction factor C = ΔθΔΨ is a constant. An analysis of measured hydraulic conductivity and porosity data suggests that the model may be useful in some soils where the changes of hydraulic characteristics with depth are of this form. A method for using the model with time variable rainfall rates is given. The model is applied to simulate the experimental results of Childs &; Bybordi (1969) who measured infiltration into layered sand profiles. Agreement was satisfactory even for this case. 相似文献
3.
Key processes in stream ecosystems are linked to hydraulic retention, which is the departure of stream flow from ideal ‘plug flow’, and reflects fluid movement through surface and hyporheic storage zones. Most existing information about hyporheic exchange is based on flume studies or field measurements in relatively steep streams with beds coarser than sand. Stream tracer studies may be used to quantify overall hydraulic retention, but disaggregation of surface and hyporheic retention remains difficult. A stream tracer approach was used to compute the rates at which stream water is exchanged with water in storage zones (total storage) in short reaches of two small, sand‐bed streams under free and obstructed flow conditions. Tracer curves were fit to the one‐dimensional transport with inflow storage model OTIS‐P. Networks of piezometers were used to measure specific discharge between the stream and the groundwater. In the sand‐bed streams studied, parameters describing total retention were in the upper 50% of data compiled from the literature, most of which represented streams with beds coarser than sand. However, hyporheic storage was an insignificant component of total hydraulic retention, representing only 0·01–0·49% of total exchange, and this fraction did not increase after installation of flow obstructions. Total retention did not vary systematically with bed material size, but increased 50–100% following flow obstruction. Removal of roughness elements, such as large wood and debris dams, is detrimental to processes dependent upon transient storage in small, sand‐bed streams. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
4.
It is shown that very strong, worldwide correlations exist between the bed concavity coefficients of a wide range of subaerial aqueous flows with exponential longitudinal profiles and both the corresponding stream segment lengths and exponential bed particle size diminution coefficients. The former correlation is complementary to an existing similar correlation for the exponential size diminution coefficients, while the latter is consistent with earlier theoretical correlations based on very limited data. The data supporting the correlations extend over virtually the whole range of stream lengths, solids concentrations, and bed sediment particle sizes found on Earth. This universality strongly suggests that there are underlying mechanisms common to all kinds of mobile bed subaerial aqueous flows. However, the scatter of the data for the correlations is significant and is mostly attributable to variations in hydraulic conditions and sediment properties rather than measurement errors. Some of the conditions and properties have been identified, but others remain obscure. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
5.
Abstract One of the basic tasks in geomorphologic analysis is to know the probability distributions of the stream lengths of different orders. In practical applications, this information is useful for basin rainfall-runoff modelling. The objective of this study is to determine the length distributions of the Strahler streams. A Poisson process was used to derive the theoretical distributions. The result showed that the length distribution of the first-order stream is an exponential distribution and the second-order or higher order stream length is a gamma distribution. In order to verify the theoretical distributions, a digital elevation model (DEM) was adopted to calculate the stream lengths of four basins in Taiwan. Kolmogorov-Smirnov and chi-square tests were used to test the goodness-of-fit of the data. Results showed that the length distributions of the first- and second-order streams analysed by using DEM correspond with those from the derived distribution method. 相似文献
6.
Fola S. Ebisemiju 《水文研究》1989,3(3):237-253
Analysis of the bankfull cross-sections of headwater streams in Ado-Ekiti region of Southwestern Nigeria and their comparison with data from other tropical environments and temperate latitudes reveal that the channel capacities of streams in the humid tropics are relatively smaller than those of temperate regions, averaging 1.51 m2 with a coefficient of variation of 87 per cent. This is attributed to the small stream discharge, the predominantly low and highly seasonal flows of the streams, the low shear stress of stream load, and the stabilizing and protective influence of riparian vegetation and surface incrustations. The chanel capacities of the urban streams (mean = 1.13m2) are about 47 per cent smaller than those of the natural streams (mean = 2.12 m2) in the same ecological zone. In terms of hydraulic efficiency, the urban streams also have relatively inefficient cross-sections and larger width/depth ratios than their rural or natural counterparts. Resurveys of seventeen monumented cross-sections reveal that while channel shoulder width increased by only 6 per cent over a one-year period, channel depth and capacity decreased by 16 per cent and 4 per cent respectively; the observed decrease in channel size occurs entirely in the channel depth dimension. Thus the response of stream channels to the urbanization of small headwater catchments in the humid tropics is probably more of vertical accretion of channel bed and reduction in channel capacity rather than the widely-reported anomalous enlargement of urban streams through channel widening. The rapid rate of channel aggradation is attributed to excessive rates of sediment production and delivery to streams in urbanized catchments in the humid tropics, rapid deposition of sediments during small runoff events and on the falling stage of storm hydrographs, and the inability of the streams to evacuate the sediments delivered to them despite the increased discharge and peak flow associated with urbanization. The low competence of the urban streams is attributed to the predominance of low flows, very gentle bed slopes, and most importantly the widespread dumping of refuse into the channels thereby reducing flow velocity and promoting backwater flooding, ponding, and sedimentation. The correlations between drainage basin area, a surrogate for stream discharge, and channel capacity are very strong for the rural watersheds, and the regression analysis indicates a tendency towards a steady-state isometric relationship. Urban channels are, to a large extent, in disequilibrium with the urban hydrological state. However, spatial variations in the degree of urbanization of the catchments, and, therefore in runoff volume and velocity, exercise strong control on channel width, depth, and size. A model of the sequence of stream channel adjustment to the urbanization of small headwater catchments in the humid tropics is presented. 相似文献
7.
8.
Low order channels comprise a large proportion of the links of every drainage basin, and are often at the centre of land management concerns. They exhibit hydrological and geomorphological characteristics atypical of higher order links. This paper examines the nature and causes of variations in the bed material texture of two streams on the Queen Charlotte Islands, British Columbia. The extant, functional exponential model is found to be inadequate for explaining observed changes in grain size parameters with distance downstream. Recurrent disruption of sediment transport by large organic debris jams, and the sporadic contamination of the fluvial sediment population by colluvial inputs, preclude the development of longitudinal structure. Rather, grain size varies erratically over short distances. A stochastic model best describes the observed variations, and should be adopted as an alternative to the exponential model in low order links. Characteristic variances are controlled by the degree of hillslope-channel coupling, and the extent and characteristics of non-alluvial storage mechanisms. 相似文献
9.
Nidal Hadadin 《国际泥沙研究》2017,32(1)
The effects of basin hydrology on hydraulic geometry of channels variability for incised streams were investigated using available field data sets and models of watershed hydrology and channel hydraulics for the Yazoo River basin,USA.The study presents the hydraulic geometry relations of bankfull discharge,channel width,mean depth,cross-sectional area,longitudinal slope,unit stream power,and mean velocity at bankfull discharge as a function of drainage area using simple linear regression.The hydraulic geometry relations were developed for 61 streams,20 of them are classified as channel evolution model(CEM) Types Ⅳ and Ⅴ and 41 of them are CEM streams Types Ⅱ and Ⅲ.These relationships are invaluable to hydraulic and water resources engineers,hydrologists,and geomorphologists involved in stream restoration and protection.These relations can be used to assist in field identification of bankfull stage and stream dimension in un-gauged watersheds as well as estimation of the comparative stability of a stream channel.A set of hydraulic geometry relations are presented in this study,these empirical relations describe physical correlations for stable and incised channels.Cross-sectional area,which combines the effects of channel width and mean channel depth,was found to be highly responsive to changes in drainage area and bankfull discharge.Analyses of cross-sectional area,channel width,mean channel depth,and mean velocity in conjunction with changes in drainage area and bankfull discharge indicated that the channel width is much more responsive to changes in both drainage area and bankfull discharge than are mean channel depth or mean velocity. 相似文献
10.
电离层掩星观测中,当低轨卫星（LEO）轨道高度较低时,轨道以上的电离层电子总含量（TEC）对掩星反演的影响不能忽略.目前,一般采用指数函数等外推方法来处理该问题,对反演结果可能引起较大误差.为提高电离层掩星反演精度,本文研究利用LEO处于非掩星一侧GPS观测数据的改正TEC新反演方法.用三维射线追踪程序计算出电离层掩星观测模拟数据,分别应用改正TEC方法和外推方法进行反演,将反演结果与所用模式值进行比较.结果表明：对于轨道高度约800km的GPS/MET掩星模拟数据,外推方法和改正TEC方法反演结果都与模式值基本一致;对于轨道高度约400km的CHAMP掩星模拟数据,外推方法误差较大,改正TEC方法反演结果与模式值相符得较好.将改正TEC方法应用于GPS/MET实测数据的反演,取得了合理的结果.这些说明,改正TEC算法是一种有效的电离层掩星反演方法,尤其是对于轨道较低的LEO的电离层掩星观测反演特别有用. 相似文献
11.
Predicting longitudinal dispersion coefficient in natural streams by artificial intelligence methods
In this study, three artificial neural network methods, i.e. feed forward back propagation, the radial basis function neural network, and the generalized regression neural network are employed to compute the longitudinal dispersion coefficient in order to evaluate its behaviour in predicting dispersion characteristics in natural streams. These methods, which use hydraulic and geometrical data to predict dispersion coefficients, can easily be applied to natural streams and are proven to be superior in explaining their dispersion characteristics more precisely than existing equations. This method of predicting the longitudinal dispersion coefficient in river flows was tested on 65 data sets, obtained by researchers from 30 rivers in the USA. Results using the models are compared with results obtained in many other studies, and are shown to be more accurate than the other methods considered. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
12.
Eric Christopher Merten Jacques Finlay Lucinda Johnson Raymond Newman Heinz Stefan Bruce Vondracek 《水文研究》2011,25(4):593-602
Wood deposited in streams provides a wide variety of ecosystem functions, including enhancing habitat for key species in stream food webs, increasing geomorphic and hydraulic heterogeneity and retaining organic matter. Given the strong role that wood plays in streams, factors that influence wood inputs, retention and transport are critical to stream ecology. Wood entrapment, the process of wood coming to rest after being swept downstream at least 10 m, is poorly understood, yet important for predicting stream function and success of restoration efforts. Data on entrapment were collected for a wide range of natural wood pieces (n = 344), stream geomorphology and hydraulic conditions in nine streams along the north shore of Lake Superior in Minnesota. Locations of pieces were determined in summer 2007 and again following an overbank stormflow event in fall 2007. The ratio of piece length to effective stream width (length ratio) and the weight of the piece were important in a multiple logistic regression model that explained 25% of the variance in wood entrapment. Entrapment remains difficult to predict in natural streams, and often may simply occur wherever wood pieces are located when high water recedes. However, this study can inform stream modifications to discourage entrapment at road crossings or other infrastructure by applying the model formula to estimate the effective width required to pass particular wood pieces. Conversely, these results could also be used to determine conditions (e.g. pre‐existing large, stable pieces) that encourage entrapment where wood is valued for ecological functions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
13.
Closed‐form solutions are proposed for natural seepage in semiconfined (leaky) aquifers such as those existing below the massive Champlain Sea clay layers in the Saint‐Lawrence River Valley. The solutions are for an ideal horizontal leaky aquifer below an ideal aquitard that may have either a constant thickness and a constant hydraulic head at its surface, or a variable thickness and a variable hydraulic head at its surface. A few simplifying assumptions were needed to obtain the closed‐form solutions. These have been verified using a finite element method, which did not make any of the assumptions but gave an excellent agreement for hydraulic heads and groundwater velocities. For example, the difference between the two solutions was smaller than 1 mm for variations in the 5 to 8 m range for the hydraulic head in the semiconfined aquifer. Note that fitting the hydraulic head data of monitoring wells to the theoretical solutions gives only the ratio of the aquifer and aquitard hydraulic conductivities, a clear case of multiple solutions for an inverse problem. Consequently, field permeability tests in the aquitard and the aquifer, and pumping tests in the aquifer, are still needed to determine the hydraulic conductivity values. 相似文献
14.
Basil Gomez 《地球表面变化过程与地形》1983,8(1):41-54
The quantitative bedload transport data that are presently available confirm that the generalized bedload transport rate-stream power relationship is applicable to natural streams. However, the bedload transport rate is not solely dependent upon hydraulic parameters, but also upon the inter-relationship between bed material characteristics and flow properties. Segregation of the surficial bed material, as expressed through the development of an armour coat, limits the availability of transportable material. Under such circumstances observed bedload transport rates are less than the predicted values. The effect which the development of an armoured surface has upon the bedload transport rate is described with reference to bedload and bed material sampling in the Borgne d'Arolla, Valais, Switzerland. The data refer to two periods when the resumption of baseflow conditions following flood events which were of a sufficient magnitude to transport all but the coarsest (0·3–0·5 m) particles on the streambed, provided the opportunity for the bed to adjust to a comparatively stable flow regime. Observed and predicted bedload transport rate-stream power relationships are compared. The theoretical relationship does not adequately describe conditions in some gravel-bed channels, since it fails to take into account the effect which armouring may have upon the supply of transportable material. 相似文献
15.
Rock and stepped gabion weirs are peculiar hydraulic structures that received relatively little attention in technical literature. Nevertheless, they can be successfully used for river restoration instead of traditional hydraulic structures. They have the advantage of being elastic structures and to preserve the natural environment. They can easily adapt to the in situ conditions and can be effortlessly modified according to the different hydraulic or geometric conditions which can occur in a natural river. The present study aims to analyze the effects of their presence on flow pattern and on the scour hole occurring downstream. The analysis involved scour processes, hydraulic jump types, stilling basin morphology and flow patterns. Two different hydraulic jump types were distinguished and classified. It was shown that the flow regime deeply influences the scour process, which evolves much more rapidly when a Skimming Flow regime takes place. Empirical relationships are proposed to evaluate maximum scour depth, maximum axial length, and non dimensional axial profiles. 相似文献
16.
Jasna Muskatirovic 《地球表面变化过程与地形》2008,33(11):1757-1768
Field data are essential in evaluating the adequacy of predictive equations for sediment transport. Each dataset based on the sediment transport rates and other relevant information gives an increased understanding and improved quantification of different factors influencing the sediment transport regime in the specific environment. Data collected for 33 sites on 31 mountain streams and rivers in Central Idaho have enabled the analysis of sediment transport characteristics in streams and rivers with different geological, topographic, morphological, hydrological, hydraulic, and sedimentological characteristics. All of these streams and rivers have armored, poorly sorted bed material with the median particle size of surface layer coarser than the subsurface layer. The fact that the largest particles in the bedload samples did not exceed the median particle size of the bed surface material indicates that the armor layer is stable for the observed flow discharges (generally bankfull or less, and in some cases two times higher than bankfull discharge). The bedload transport is size‐selective. The transport rates are generally low, since sediment supply is less than the ability of flow to move the sediment for one range of flow discharges, or, the hydraulic ability of the stream is insufficient for entrainment of the coarse bed material. Detailed analyses of bedload transport rates, bedload and bed material characteristics were performed for each site. The obtained results and conclusions are used to identify different influences on bedload transport rates in analyzed gravel‐bed rivers. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
17.
Stream–subsurface water interaction induced by natural riffles and constructed riffles/steps was examined in lowland streams in southern Ontario, Canada. The penetration of stream water into the subsurface was analysed using hydrometric data, and the zone of > 10% stream water was calculated from a chemical mixing equation using tracer injection of bromide and background chloride concentrations. The constructed riffles studied induced more extensive hyporheic exchange than the natural riffles because of their steeper longitudinal hydraulic head gradients and coarser streambed sediments. The depth of > 10% stream water zone in a small and a large constructed riffle extended to > 0·2 m and > 1·4 m depths respectively. Flux and residence time distribution of hyporheic exchange were simulated in constructed riffles using MODFLOW, a finite‐difference groundwater flow model. Hyporheic flux and residence time distribution varied along the riffles, and the exchange occurring upstream from the riffle crest was small in flux and had a long residence time. In contrast, hyporheic exchange occurring downstream from the riffle crest had a relatively short residence time and accounted for 83% and 70% of total hyporheic exchange flow in a small and large riffle respectively. Although stream restoration projects have not considered the hyporheic zone, our data indicate that constructed riffles and steps can promote vertical hydrologic exchange and increase the groundwater–surface water linkage in degraded lowland streams. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
18.
Mark R. Welford 《地球表面变化过程与地形》1994,19(4):287-297
This study investigates the fluvial dynamics of straight natural stream channels. In particular, this experimental field study quantitatively assesses a physically based non-linear mathematical theory of alternate bar formation under unsteady natural flow conditions within a straight alluvial stream. The study site is an artificially straightened section of the Embarras River located approximately 16 km south of Champaign, Illinois. Data were collected on channel form, gradient, alternate bar dimensions, bed sediment size and flow stage over a 2 year study period. Both linear and non-linear steady flow hydrodynamic theories suggest that alternate bars are critical to the process of meander development. But these theories do not predict bar development for unsteady flow conditions, which typically occur in natural alluvial channels. Tubino (1991) suggests that bar evolution for a flood hydrograph can be divided into three parts: (1) a period of limited bar growth during the rising stage of the flood; (2) a stage of modest bar decay near the peak of the flood; and (3) a stage of non-linear bar growth during the prolonged falling stage of the flood. Bars developed during the falling limb of a hydrograph, and exhibited sequential development rather than the uniform growth along the reach predicted by Tubino's model. As flow stage decreased, short, low, fine-grained bars were superimposed on long, high and coarser-grained bars that developed under preceding high flow stages. These results suggest that the process of bar formation in artificially straightened natural streams with heterogeneous bed material may occur under different flow conditions and in a different manner than predicted by theoretical models. Further work should focus on attempting to isolate the physical mechanisms responsible for alternate bar formation in straight natural streams with heterogeneous bed material and flashy hydrologic flow regimes. 相似文献
19.
A stochastic model for synthetic data generation is not available in the literature for daily flows of intermittent streams. Such a model is required in the planning and operation of structures on an intermittent stream for purposes where short time flow fluctuations are important. In this study a model is developed for such a case. The model consists of four steps: determination of the days on which flow occurs, determination of the days on which a flow increment occurs, determination of the magnitude of the flow increment, and calculation of the flow decrement on days when the flow is reduced. The first two steps are modelled by a three‐state Markov chain. In the third step, flow increments on the rising limb of the hydrograph are assumed to be gamma distributed. In the last step an exponential recession is used with two different coefficients. Parameters of the model are estimated from the observed daily stream flow data for each month of the year. The model is applied to a daily flow series of 35 years' length. It is seen that the model can preserve the short‐term characteristics (the ascension and recession curves and peaks) of the hydrograph in addition to the long‐term characteristics (mean, variance, skewness, lag‐one and higher lag autocorrelation coefficients, and zero flow percentage). The number of parameters of the model can be decreased by fitting Fourier series to their annual variation. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
20.
P. A. Carling 《地球表面变化过程与地形》1991,16(1):19-31
The ‘velocity-reversal hypothesis’ is the linchpin for a number of recent conceptual models pertaining to sediment sorting and the maintenance of pool-riffle sequences in gravel-bedded streams. The literature in support of the hypothesis together with published adverse criticism is reviewed. It is concluded that convincing evidence for the ubiquitous occurrence of such a reversal in a range of channel geometries is currently unavailable. Continuity considerations indicate that riffles need to be considerably wider than pools for a reversal in the mean velocity to occur under conditions of subcritical flow, high stage, and stable morphology. These observations are substantiated by a detailed study of the hydraulic geometry of stable pool-riffle sequences in the River Severn, England. Neither the sectionally-averaged velocity nor the near-bed shear velocity is sensibly greater in the pools than over the riffles during bankfull or near bankfull flow. Instead a tendency towards equalization of the values of average hydraulic variables is noted as discharge increases. A detailed investigation of the three-dimensional character of the flow is required to demonstrate whether the entrainment forces within pools can locally exceed those over neighbouring riffles. Unusual behaviour of the energy gradient over riffles during moderate discharges is related to backwater effects as mediated by the spacing of the riffles. The hydraulic data are used to comment on the stability of the test reaches in the context of the development of the River Severn in the vicinity of Shrewsbury. 相似文献