Effect of saltating sediment on flow resistance and bred roughness in overlandflow
This study has evaluated the effect of saltating sediment on flow resistance and bed roughness in overlandflow on a fixed sand-covered bed. It is concluded that saltating sediment has a considerable impact on overlandflow hydraulics, at least
on fixed granular beds. Saltation is likely to have a relatively smaller effect on overlandflow on natural hillslopes and agricultural fields where form and wave resistance dominate.
Size characteristics of sediment in interrill overlandflow on a semiarid hillslope, southern Arizona
The aim of this study is to examine and consider the significance of the size characteristics of sediment removed in interrill overlandflow in a semiarid environment on a plot covered by natural vegetation, undisturbed by agricultural practices
, and large enough to encompass the full range of interill overlandflow.
Inception of sediment transport in shallow overlandflow
Model ; Overlandflow ; Rill wash;Runoff ; Sediment transport ; Soil erosion
Literature suggests that the Shields criterion is not well suited to predicting the inception of sediment transport in overlandflow. A new approach to transport inception in overlandflow is proposed, which avoids measurement difficulties
and friction law uncertainties. A preliminary model, valid for uniform flow over non-cohesive material, is developed.
This paper presents a simple understanding-oriented model based on the conditioned-walker technique. This model simulates overland-flow triggering, i.e. the development of water transfer among depressions and to the runoff boundary. By the use
of relevant measurements, the paper intends to provide further understanding about the control of overland-flow by the surface roughness due to the storage of water by depressions.
The aim of this paper is to pose a broad model for the hydraulics of overlandflow by assessing the dependence of the friction factor on an inundation ratio at 3 stages of progressive flow inundation. The development of the model is prefaced
by a brief review of the physical variables which may contribute to flow resistance and some of the possible dimensionless groupings arising from those variables. Previously published field and laboratory data are re-evaluated in terms of the frictional
resistance as a function of an estimated inundation ratio for each flow, and the results are compared with the trends predicted by the model.
The aim of this study is to evaluate the effect of bed mobility on resistance to overlandflow on rough beds. This is done by analyzing 2 series of flume experiments with similar hydraulic and bed roughness characteristics. In the first series
the water is free of sediment and flows over a fixed bed, whereas in the second the water is laden with sediment and flows over a mobile bed. Discussion of the results.
Effects of surface water storage by soil roughness on overland-flow generation
This study analyses effects of surface roughness on overland-flow by means of a model simulating depression filling, flow pathways and runoff generation. It examines the relevant characteristics of surface roughness using numerically generated
surfaces. Three surface descriptions are considered. First, the sensitivity of overland-flow triggering to surface correlation properties is addressed. Secondly, effects of the short-range correlation are studied. Thirdly, combined effects of random
Overlandflow and soil erosion : some processes and their interactions
Carrying capacity ; Flow ; Model ; Overlandflow ; Sediment transport ; Soil erosion
Flow detachment, sediment transport and interactions between flow characteristics and sediment load are discussed here. Descriptions of the interactions between sediment load and flow characteristics, namely mean flow velocity, obtained through
Initiation of motion of gravels in concentrated overlandflow : cohesive forces and probability of entrainment
Experimentation ; Model ; Overlandflow ; Probability ; Sediment transport ; Soil erosion ; Turbulence
Threshold conditions for entrainment of gravel by concentrated overlandflow are here discussed. The measured data indicate that cohesive forces may arise and must be taken into account by the models describing grain entrainment. Some models
Threshold relations for the transport of sediment by overlandflow on desert hillslopes
This study investigates the ability of the Shields relation to predict the initiation of sediment transport by overlandflow on desert hillslopes. The Shields relation is evaluated using data collected from a series of overlandflow experiments
This study examines the validity of linear superposition approach when rainfall and surface roughness are considered in overlandflow resistance. To examine a possible interference in flow resistance, a set of flume experiments using surface objects
in overlandflow resistance.
and rainfall as roughness elements were conducted. Since the flow resistance due to each element cannot be measured directly, the linear superposition equation had to be rewritten using friction factor increment as variable. The result shows
A unit stream power based sediment transport function for overlandflow
Concept ; Model ; Overlandflow ; Sediment transport ; Soil erosion ; Statistical analysis ; Water erosion ; Watershed
The suitability of 5 sediment transport capacity functions was evaluated for overlandflow conditions using graphical and statistical analysis. The results show that the application of these functions is limited to the range of hydraulic
and sediment conditions for which each was formulated. To improve predictions of transport capacity under overlandflow conditions, especially at low flow intensities, a new function, based on the unit stream power concept, was derived using experimental data.
Large roughness elements such as stones or plant stems (obstacles) influence the depth of overlandflows in 2 ways. The first effect is a dynamic one, involving frictional retardation of the flow and associated reduction in flow speeds. The second
influence is static, and arises from the upward volumetric displacement of flow depth because of the submerged volume of the obstacles.To understand the true frictional drag arising from obstacles , a correction must be made for the volumetric displacement
Hydraulics of interrill overlandflow on rough, bare soil surfaces
Model ; Overlandflow ; Rill wash ; Roughness ; Slope
on detailed surface roughness data. Roughness profiles perpendicular to the flow are used to calculate the wet cross-sectional area and hydraulic radius given a certain water level. The algorithm of Savat is then applied to calculate the hydraulic resistance
. The model is able to predict flow velocities reasonably well from discharge and roughness data only.
The data for this study come from 54 flume experiments with fixed beds and 38 with mobile beds. The results imply that mobile beds offer greater resistance to flow than do fixed beds. Grain collisions with mobile beds are less elastic than those
Hydraulics of interrill overlandflow on stone-covered desert surfaces
The hydraulics of composite overlandflow around surface stones are extremely complex and have been little studied. The purpose of this paper is to review both field and laboratory research on this subject and to discuss briefly the implications