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1.
Runoff and sediment were measured from agricultural land exposed to controlled simulated rainfall. We extended the kinematic unsteady overland sedimentation theory of prismatic channels to the experiments by considering both hydraulics and sediment dynamics of rill flow for changing flow geometries of nonuniform and unsteady rill development. The characteristic unimodal concentration peak observed in the experiments and the changing channel geometry were interpreted in theoretical terms. Overland sedimentation in unsteady nonprismatic rills under uniform rainfall can be described with kinematic models of flow, entrainment and deposition applied to developing flow geometries; this is not possible with sheet-flow models. Other interpretations are considered and experimental needs are identified. 相似文献
2.
Predicting the behavior of overland flow with analytical solutions to the kinematic wave equation is appealing due to its relative ease of implementation. Such simple solutions, however, have largely been constrained to applications on simple planar hillslopes. This study presents analytical solutions to the kinematic wave equation for hillslopes with modest topographic curvature that causes divergence or convergence of runoff flowpaths. The solution averages flow depths along changing hillslope contours whose lengths vary according hillslope width function, and results in a one-dimensional approximation to the two-dimensional flow field. The solutions are tested against both two-dimensional numerical solutions to the kinematic wave equation (in ParFlow) and against experiments that use rainfall simulation on machined hillslopes with defined curvature properties. Excellent agreement between numerical, experimental and analytical solutions is found for hillslopes with mild to moderate curvature. The solutions show that curvature drives large changes in maximum flow rate qpeak and time of concentration tc , predictions frequently used in engineering hydrologic design and analysis. 相似文献
3.
Sediment transport in rill flows exhibits the characteristics of non‐equilibrium transport, and the sediment transport rate of rill flow gradually recovers along the flow direction by erosion. By employing the concept of partial equilibrium sediment transport from open channel hydraulics, a dynamic model of rill erosion on hillslopes was developed. In the model, a parameter, called the restoration coefficient of sediment transport capacity, was used to express the recovery process of sediment transport rate, which was analysed by dimensional analysis and determined from laboratory experimental data. The values of soil loss simulated by the model were in agreement with observed values. The model results showed that the length and gradient of the hillslope and rainfall intensity had different influences on rill erosion. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
4.
Fen-liZHENG Pei-qingXIAO Xue-tianGAO 《国际泥沙研究》2004,19(2):130-141
In the rill erosion process, run-on water and sediment from upslope areas, and rill flow hydraulic parameters have significant effects on sediment detachment and transport. However, there is a lack of data to quantify the effects of run-on water and sediment and rill flow hydraulic parameters on rill erosion process at steep hillslopes, especially in the Loess Plateau of China. A dual-box system, consisting of a 2-m-long feeder box and a 5-m-long test box with 26.8% slope gradient was used to quantify the effects of upslope runoff and sediment, and of rill flow hydraulic parameters on the rill erosion process. The results showed that detachment-transport was dominated in rill erosion processes; upslope runoff always caused the net rill detachment at the downslope rill flow channel, and the net rill detachment caused by upslope runoff increased with a decrease of runoff sediment concentration from the feeder box or an increase of rainfall intensity. Upslope runoff discharging into the rill flow channel or an increase of rainfall intensity caused the rill flow to shift from a stratum flow into a turbulent flow. Upslope runoff had an important effect on rill flow hydraulic parameters, such as rill flow velocity, hydraulic radius, Reynolds number, Froude number and the Darcy-Weisbach resistance coefficient. The net rill detachment caused by upslope runoff increased as the relative increments of rill flow velocity, Reynolds number and Froude number caused by upslope runoff increased. In contrast, the net rill detachment decreased with an increase of the relative decrement of the Darcy-Weisbach resistance coefficient caused by upslope runoff. These findings will help to improve the understanding of the effects of run-on water and sediment on the erosion process and to find control strategies to minimize the impact of run-on water. 相似文献
5.
Flow energy and channel adjustments in rills developed in loamy sand and sandy loam soils 总被引：1，自引：0，他引：1
The storms usually associated with rill development in nature are seldom prolonged, so development is often interrupted by interstorm disturbances, e.g. weathering or tillage. In laboratory simulated rainfall experiments, active rill development can be prolonged, and under these conditions typically passes through a period of intense incision, channel extension and bifurcation before reaching quasi‐stable conditions in which little form change occurs. This paper presents laboratory experiments with coarse textured soils under simulated rainfall which show how channel adjustment processes contribute to the evolution of quasi‐stability. Newly incised rills were stabilized for detailed study of links between rill configuration and flow energy. On a loamy sand, adjustment towards equilibrium occurred due to channel widening and meandering, whereas on a sandy loam, mobile knickpoints and chutes, pulsations in flow width and flow depth and changes in stream power and sediment discharge occurred as the channel adjusted towards equilibrium. The tendency of rill systems towards quasi‐stability is shown by changes in stream power values which show short‐lived minima. Differences in energy dissipation in stabilized rills indicate that minimization of energy dissipation was reached locally between knickpoints and at the downstream ends of rills. In the absence of energy gradients in knickpoints and chutes, stabilized rill sections tended toward equilibrium by establishing uniform energy expenditure. The study confirmed that energy dissipation increased with flow aspect ratio. In stabilized rills, flow acceleration reduced energy dissipation on the loamy sand but not on the sandy loam. On both soils flow deceleration tended to increase energy dissipation. Understanding how rill systems evolve towards stability is essential in order to predict how interruptions between storms may affect long‐term rill dynamics. This is essential if event‐based physical models are to become effective in predicting sediment transport on rilled hillslopes under changing weather and climatic conditions. Copyright © 2008 John Wiley and Sons, Ltd. 相似文献
6.
AbstractA physically-based hillslope hydrological model with shallow overland flow and rapid subsurface stormflow components was developed and calibrated using field experiments conducted on a preferential path nested hillslope in northeast India. Virtual experiments were carried out to perform sensitivity analysis of the model using the automated parameter estimation (PEST) algorithm. Different physical parameters of the model were varied to study the resulting effects on overland flow and subsurface stormflow responses from the theoretical hillslopes. It was observed that topographical shapes had significant effects on overland flow hydrographs. The slope profiles, surface storage, relief, rainfall intensity and infiltration rates primarily controlled the overland flow response of the hillslopes. Prompt subsurface stormflow responses were mainly dominated by lateral preferential flow, as soil matrix flow rates were very slow. Rainfall intensity and soil macropore structures were the most influential parameters on subsurface stormflow. The number of connected soil macropores was a more sensitive parameter than the size of macropores. In hillslopes with highly active vertical and lateral preferential pathways, saturation excess overland flow was not evident. However, saturation excess overland flow was generated if the lateral macropores were disconnected. Under such conditions, rainfall intensity, duration and preferential flow rate governed the process of saturation excess overland flow generation from hillslopes.
Editor D. Koutsoyiannis; Associate editor C. Perrin 相似文献
7.
Coupling the Xinanjiang model to a kinematic flow model based on digital drainage networks for flood forecasting 总被引：1，自引：0，他引：1
The Xinanjiang model, which is a conceptual rainfall‐runoff model and has been successfully and widely applied in humid and semi‐humid regions in China, is coupled by the physically based kinematic wave method based on a digital drainage network. The kinematic wave Xinanjiang model (KWXAJ) uses topography and land use data to simulate runoff and overland flow routing. For the modelling, the catchment is subdivided into numerous hillslopes and consists of a raster grid of flow vectors that define the water flow directions. The Xinanjiang model simulates the runoff yield in each grid cell, and the kinematic wave approach is then applied to a ranked raster network. The grid‐based rainfall‐runoff model was applied to simulate basin‐scale water discharge from an 805‐km2 catchment of the Huaihe River, China. Rainfall and discharge records were available for the years 1984, 1985, 1987, 1998 and 1999. Eight flood events were used to calibrate the model's parameters and three other flood events were used to validate the grid‐based rainfall‐runoff model. A Manning's roughness via a linear flood depth relationship was suggested in this paper for improving flood forecasting. The calibration and validation results show that this model works well. A sensitivity analysis was further performed to evaluate the variation of topography (hillslopes) and land use parameters on catchment discharge. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
8.
1 INTRODUCTIONThe prediction of future impacts on terrestrial ecosystems by atmospheric, climatic and land-usechanges is the aim of watershed management. Meeting these requirements scientists, managers and policymakers try to achieve the sustainable management of the vitally important resources of watersheds due toan integrated ecosystem approach at the catchment scale. As composite landscapes often have a highdegree of contingency between its elements, the transport over these landscape s… 相似文献
9.
The objective of this work is to analyse the storage–flux hysteretic behaviour of a simplified model for subsurface flow processes. The subsurface flow dynamics is analysed by means of a model based on the kinematic wave assumptions and by using a width weighting/depth averaging scheme which allows to map the three-dimensional soil mantle into a one-dimensional profile. Continuity and a kinematic form of Darcy’s law lead to a hillslope-storage kinematic wave equation for subsurface flow, solvable with the method of characteristics. Adopting a second order polynomial function to describe the bedrock slope and an exponential function to describe the variation of the width of the hillslope with hillslope distance, we derive general solutions to the hillslope-storage kinematic wave equations, applicable to a wide range of hillslopes. These solutions provide a physical basis for deriving two geometric parameters α and ψ which define the hydrological similarity between hillslopes with respect to their characteristic response and hysteresis. The hysteresis η, quantified by the area of the hysteretic dimensionless loop, has been therefore computed for a range of values of parameters α and ψ. Slopes exhibit generally clockwise hysteretic loop in the flux-storage plot, with higher groundwater mean volume for given discharge on rising limb than at same discharge on falling limb. It has been found that hysteresis increases with decreasing α and ψ, i.e. with increasing convergence (for the shape) and concavity (for the profile), and vice versa. For relatively large values of α and ψ the hysteresis may take a complex pattern, with combination of clockwise to anticlockwise loop cycles. Application of the theory to three hillslopes in the Eastern Italian Alps provides an opportunity to examine how natural topographies are represented by the two hillslope hydrological similarity parameters. 相似文献
10.
The similarity solutions of the equations of kinematic flow on a cone-shaped surface, provide a means for checking the numerical models used for converging and diverging flows. These models can be further improved if the initial excess rainfall curve can be described as a power of time. Illustration of this improvement and assessment of numerical models are given for a constant excess rainfall and for excess rainfall proportional to the inverse of the square root of time. 相似文献
11.
The kinematic‐wave and diffusive‐wave approximations were investigated for unsteady overland flow resulting from spatially varying rainfall excess. Three types of boundary conditions were adopted: zero flow at the upstream end, and critical flow and zero depth‐gradient at the downstream end. Errors were derived by comparing the dimensionless profiles of the flow depth over the plane with those computed from the dynamic‐wave solution. It was found that the mean errors for both the approximations were independent of the type of rainfall excess distribution for KF02 > 5, where K is the kinematic‐wave number and F0 is the Froude number. Therefore, the regions (KF02, F0) where the kinematic‐wave and diffusive‐wave solutions would be fairly accurate and for any distribution of spatially varying rainfall, were characterized. The kinematic‐wave approximation was reasonably accurate, with a mean error of less than 5% and for the critical depth at the downstream end, for KF02 ≥ 20 with F0 ≤ 1; if the rainfall excess was concentrated in a portion of the plane, the field where the kinematic‐wave solution was found accurate, it was more limited and characterized for KF02 > 35 with F0 ≤ 1. The diffusive‐wave solution was in good agreement with the dynamic‐wave solution with a mean error of less than 5%, in the flow depth, for KF02 ≥ 15 with F0 ≤ 1; for rainfall excess concentrated in a portion of the plane, the accuracy of the diffusion wave solution was in a region more restricted and defined for KF02 ≥ 30 with F0 ≤ 1. For zero‐depth gradient at the downstream end, the accuracy field of the kinematic‐wave was found to be greater and characterized for KF02 > 10 with F0 ≤ 1; for rainfall excess concentrated in a portion of the plane, the region was smaller and defined for KF02 > 15 with F0 ≤ 1. The diffusive‐wave solution was found accurate in the region defined for KF02 > 7·5, whereas for rainfall excess concentrated in a portion of the plane, the field of accuracy was for KF02 > 12·5 with F0 ≤ 1. The lower limits of the regions, defined on KF02, can be considered generally valid for both approximations, but for F0 < 1 smaller lower limits were also characterized. Finally, the accuracy of these approximations was influenced significantly by the downstream boundary condition. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
12.
A mathematical model was developed for simulating runoff generation and soil erosion on hillslopes. The model is comprised of three modules: one for overland flow, one for soil infiltration, and one for soil erosion including rill erosion and interrill erosion. Rainfall and slope characteristics affecting soil erosion on hillslopes were analysed. The model results show that the slope length and gradient, time distribution rainfall, and distribution of rills have varying influence on soil erosion. Erosion rate increases nonlinearly with increase in the slope length; a long slope length leads to more serious erosion. The effect of the slope gradient on soil erosion can be both positive and negative. Thus, there exists a critical slope gradient for soil erosion, which is about 45° for the rate of erosion at the end of the slope and about 25° for the accumulated erosion. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
13.
WU Changwen WANG Lixian 《国际泥沙研究》1995,(1)
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14.
We propose an improvement of the overland‐flow parameterization in a distributed hydrological model, which uses a constant horizontal grid resolution and employs the kinematic wave approximation for both hillslope and river channel flow. The standard parameterization lacks any channel flow characteristics for rivers, which results in reduced river flow velocities for streams narrower than the horizontal grid resolution. Moreover, the surface areas, through which these wider model rivers may exchange water with the subsurface, are larger than the real river channels potentially leading to unrealistic vertical flows. We propose an approximation of the subscale channel flow by scaling Manning's roughness in the kinematic wave formulation via a relationship between river width and grid cell size, following a simplified version of the Barré de Saint‐Venant equations (Manning–Strickler equations). The too large exchange areas between model rivers and the subsurface are compensated by a grid resolution‐dependent scaling of the infiltration/exfiltration rate across river beds. We test both scaling approaches in the integrated hydrological model ParFlow. An empirical relation is used for estimating the true river width from the mean annual discharge. Our simulations show that the scaling of the roughness coefficient and the hydraulic conductivity effectively corrects overland flow velocities calculated on the coarse grid leading to a better representation of flood waves in the river channels. 相似文献
15.
Rill network development not only potentially affects hillslope and drainage network evolution, but also causes severe soil degradation. However, the studies on rill network development remain inconclusive. This study aimed to investigate the temporal and spatial development of hillslope rill networks and their characteristics based on rainfall simulations and field observations. A soil pan (10.0 m long × 3.0 m wide × 0.5 m deep) on a 20° slope was applied three successive simulated rains at two intensities of 50 and 100 mm h–1. The field observations were performed on two bare hillslope runoff plots (10.0 m long × 3.0 m wide) at 20°. Three typical erosive natural rainfall events were observed in the field, and rills were measured in detail, similar to the laboratory rainfall simulation. The results indicated that with increases in rainfall events, the rill network morphology varied from incipient formation to the maximum drainage network density. Four rill network development indicators (rill distribution density, distance between rills, rill bifurcation number, and confluence point number) exhibited different changes over time and space. Among the four indicators, the rill bifurcation number was the best indicator for describing rill network development. Rill flow energy increased and decreased cyclically on a slope ranging between ~3 and 4 m. Moreover, rill networks on loessial hillslopes generally evolved into dendritic rather than parallel forms. The development characteristics of the rill network were relatively similar between the laboratory simulation and natural field conditions. Over time, rill erosion control measures become increasingly difficult to implement as the rill network develops. The morphology of eroding rills evolved over time and space, which led to corresponding rill network development. Further study should quantify the impacts of rill network development on soil degradation and land development. © 2020 John Wiley & Sons, Ltd. 相似文献
16.
Infiltration,runoff and sediment production in blanket peat catchments: implications of field rainfall simulation experiments 总被引：1，自引：0，他引：1
Blanket peat covers the headwaters of many major European rivers. Runoff production in upland blanket peat catchments is flashy with large flood peaks and short lag times; there is minimal baseflow. Little is known about the exact processes of infiltration and runoff generation within these upland headwaters. This paper presents results from a set of rainfall simulation experiments performed on the blanket peat moorland of the North Pennines, UK. Rainfall was simulated at low intensities (3–12 mm h?1), typical of natural rainfall, on bare and vegetated peat surfaces. Runoff response shows that infiltration rate increases with rainfall intensity; the use of low‐intensity rainfall therefore allows a more realistic evaluation of infiltration rates and flow processes than previous studies. Overland flow is shown to be common on both vegetated and bare peat surfaces although surface cover does exert some control. Most runoff is produced within the top few centimetres of the peat and runoff response decreases rapidly with depth. Little vertical percolation takes place to depths greater than 10 cm owing to the saturation of the peat mass. This study provides evidence that the quickflow response of upland blanket peat catchments is a result of saturation‐excess overland flow generation. Rainfall–runoff response from small plots varies with season. Following warm, dry weather, rainfall tends to infiltrate more readily into blanket peat, not just initially but to the extent that steady‐state surface runoff rates are reduced and more flow takes place within the peat, albeit at shallow depth. Sediment erosion from bare peat plots tends to be supply limited. Seasonal weather conditions may affect this in that after a warm, dry spell, surface desiccation allows sediment erosion to become transport limited. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
17.
Physically based modelling of sheet erosion (detachment and deposition processes) in complex hillslopes 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Ali Talebi Rasoul Hajiabolghasemi Mohamad Reza Hadian Nosratollah Amanian 《水文研究》2016,30(12):1968-1977
A one‐dimensional uncoupled model governed by this research is a physics‐based modelling of the rainfall‐runoff induced erosion process. The presented model is composed of three parts of a three‐dimensional (3D) hillslope geometry, a nonlinear storage (kinematic wave) model for hillslope hydrological response, and an unsteady physically based surface erosion model. The 3D hillslope geometry model allows describing of the hillslope morphology by defining their plan shape and profile curvature. By changing these two topographic parameters, nine basic hillslope types are derived. The modelling of hillslope hydrological response is based on a flow continuity equation as the relation of discharge and flow depth is passed on kinematic wave approximation. The erosion model is based on a mass conservation equation for unsteady flow. The model assumes that suspended sediment does not affect flow dynamics. The model also accounts for the effect of flow depth plus loose soil depth on soil detachment. The presented model was run for two different precipitations, slope content, and length, and results were plotted for sediment detachment/deposition rate. Based on the obtained results, in hillslopes with convex and straight profile curvatures, sediment detachment only occurred in the whole length of the hillslope. However, in concave ones, sediment detachment and deposition only occurred together in hillslope. The hillslopes with straight profiles and convergent plans have the highest rate of detachment. Also, results show that most detachment rates occur in convex profile curvatures, which are about 15 times more than in straight profiles. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
18.
IntheLoessPlateau,alongtheslopelengthfromthetoptothebottom,soilerosionischaracterizedbyobviousverticalzonaldivision,thatis,sheeterosionzone,sheeterosionandrillerosionzone,rillerosionandshallowgullyerosionzoneandgullyerosionzone.Inthesheetandrillero..sionzone,rillerosionamounttakesup70%ofthetotalsoilloss[TANGKenetal.,1983,ZHENGFenlietal.,19871;intherillandshallowgullyerosionzone,rillerosionamountaccountsfor30--40%ofthetotalsoilloss.Sorillerosionisamajorerosionpatternonsteepslopeland.Riller… 相似文献
19.
The behaviour of river waves is described using a simplified dimensionless form of the momentum equation in conjunction with the continuity equation. Three dimensionless parameters were derived based on a quantitative linear analysis. These parameters, which depend on the Froude number of the steady uniform flow and the geometric characteristics of the river, permit quantification of the influence of inertia and pressure in the momentum equation. It was found that dynamic and diffusion waves occur mainly on gentle channel slopes and the transition between them is characterized by the Froude number. On the other hand, the kinematic wave has a wide range of applications. If the channel slope is greater than 1%, the kinematic wave is particularly suitable for describing the hydraulics of flow. Since slopes in natural channel networks are often greater than 1%, an analytical solution of the linearized kinematic wave equation with lateral inflow uniformly distributed along the channel is desirable and was therefore derived. The analytical solution was then implemented in a channel routing module of an existing simple rainfall–runoff model. The results obtained using the analytical solution compared well with those obtained from a non‐linear kinematic wave model. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
20.
Water flow velocity is an important hydraulic variable in hydrological and soil erosion models, and is greatly affected by freezing and thawing of the surface soil layer in cold high-altitude regions. The accurate measurement of rill flow velocity when impacted by the thawing process is critical to simulate runoff and sediment transport processes. In this study, an electrolyte tracer modelling method was used to measure rill flow velocity along a meadow soil slope at different thaw depths under simulated rainfall. Rill flow velocity was measured using four thawed soil depths (0, 1, 2 and 10 cm), four slope gradients (5°, 10°, 15° and 20°) and four rainfall intensities (30, 60, 90 and 120 mm·h−1). The results showed that the increase in thawed soil depth caused a decrease in rill flow velocity, whereby the rate of this decrease was also diminishing. Whilst the rill flow velocity was positively correlated with slope gradient and rainfall intensity, the response of rill flow velocity to these influencing factors varied with thawed soil depth. The mechanism by which thawed soil depth influenced rill flow velocity was attributed to the consumption of runoff energy, slope surface roughness, and the headcut effect. Rill flow velocity was modelled by thawed soil depth, slope gradient and rainfall intensity using an empirical function. This function predicted values that were in good agreement with the measured data. These results provide the foundation for a better understanding of the effect of thawed soil depth on slope hydrology, erosion and the parameterization scheme for hydrological and soil erosion models. 相似文献