Showing papers on "Stream power published in 1998"

Bed material transport estimated from the virtual velocity of sediment

Abstract: This study evaluates the possibility of determining bed material transport using the virtual rate of travel of individual particles, dimensions of the active layer of the streambed, and porosity and density of streambed material. Magnetically tagged stones and scour indicators were employed in Carnation Creek, British Columbia, to quantify transport rates. Observations cover flows up to 36 m3 s−1 (τ* = 0·081). Transport rates, ranging from 0·090 to 9·7 kg s−1 (0·12–13·2 m3 h−1), display a relatively sensitive trend with maximum stream power, as expected. Error analysis indicates that uncertainty in virtual velocity covers the majority of sample variance. An evaluation of the two measurement techniques used to delineate active layer dimensions, magnetically tagged stones and scour indicators, indicates that they yield comparable depths, widths and transport rates over the range of flows observed. Issues for further study are discussed. © 1998 John Wiley & Sons, Ltd.

Rill erosion and morphological evolution: A simulation model

Abstract: A mathematical model is advanced to simulate dynamically and spatially varied shallow water flow and soil detachment, transport, and deposition in rills The model mimics the dynamic process of rill evolution, including variable rates of sediment redistribution along the bed and changes in local bed morphology The sediment source term in the model uses a point scale, probabilistic relationship based on turbulent flow mechanics and a recently developed sediment transport relationship for rills based on stream power The interdependent feedback loops between channel bed morphology, local flow hydraulics, and local scour and deposition, within the framework of the full hydrodynamic equations with inertial terms, constitute a mathematical model with the capacity to represent spatial variability and temporal evolution of the rill Finite elements were applied to numerically solve the hydrodynamic and sediment continuity equations A series of laboratory flume experiments were performed to evaluate the model Initial bed slopes were 3, 5, and 7% with step increases of water inflow rates of 76, 114, and 152 L min−1 The soil material used in the flume was a kaolinitic, sandy-clay loam The rill model equations were solved for increasingly complex cases of spatial and temporal variabilities The model followed measured patterns of morphological changes as the rill evolved, which suggests that the feedback loops in the model between erosion, bed morphological changes, and hydraulics were adequate to capture the essence of rill evolution

Patterns of Bedrock Channel Erosion on the Boso Peninsula, Japan

Abstract: Three channels on the Boso Peninsula, Japan, were examined to assess how cross‐sectional to reach‐scale channel morphology relates to substrate variables, and how cross‐sectional to reach‐scale erosional patterns relate to basin‐scale longitudinal profile. Two of the channels, Shichiri‐gawa and Torii‐zawa are deeply incised into interbedded sandstone and mudstone, whereas the third channel, Futama‐gawa, is incised into mudstone. Reach‐scale channel morphologies include knickpoints, chutes and pools, plane beds, and both transverse and longitudinal bed erosional features. Step‐backwater modeling of a September 1996 typhoon‐related flood flow along each channel indicated that unit stream power is highly variable downstream. Stream power minima are associated with bends and with coarse‐clast deposition. Magnitude of erosional bed features correlates with hydraulics and flow energy expenditure along Futama‐gawa, and with variability in substrate resistance along Shichiri‐gawa and Torii‐zawa. Thickness and ori...

Types of river channel patterns and their natural controls

Abstract: River channel patterns are thought to form a morphological continuum. This continuum is two-dimensional, defined by plan features of which there are three (straight, meandering, branching), and structural levels of fluvial relief of which there are also three (floodplain, flood channel, low-water channel). Combinations of these three categories define the diversity of patterns. One of the most important factors in channel development is stream power, defined by water discharge and river slope. The greater the stream power, the stronger the branching tendency, but threshold values of stream power are different for the three different hierarchical levels of channel relief. The critical stream power values and hydrological regime together define the channel pattern, and analysis of the pattern type can be undertaken using effective discharge curves. © 1998 John Wiley & Sons, Ltd.

Evaluating overland flow sediment transport capacity

Abstract: An equation for evaluating the sediment transport capacity of overland flow is a necessary part of a physically based soil erosion model describing sediment detachment and transport as distributed processes. At first, for the hydraulic conditions of small-scale and large-scale roughness, the sediment transport capacity relationship used in the WEPP model is calibrated by Yalin and Govers' equation. The analysis shows that the transport coefficient Kt depends on the Shields parameter, Y, according to a semi-logarithmic (Yalin) or a linear (Govers) equation. The reliability of the semi-logarithmic equation is verified by Smart's, and Aziz and Scott's experimental data. Then the Low's formula, whose applicability is also proved by Smart's, and Aziz and Scott's data, is transformed as a stream power equation in which a stream power coefficient, KSP, depending on Shields parameter, slope, sediment and water-specific weight, appears. A relationship between transport capacity and effective stream power is also proposed. Finally, the influence of rainfall on sediment transport capacity and the prediction of critical shear stress corresponding to overland flow are examined. © 1998 John Wiley & Sons, Ltd.

Erosion, deposition and basin-wide variations in stream power and bed shear stress

Abstract: Field data from four separate locations indicate that the rate at which river channel gradient decreases downstream is fundamentally different in areas of long-term erosion and deposition. Gradient (S) and distance from the drainage divide (x) are related such that S is proportional to xΦ. In areas of deposition Φ −1.1. These differences produce downstream increases and decreases in stream power and bed shear stress which also coincide with areas of erosion and deposition. This is the first time that such a basin-wide coincidence has been demonstrated. A strong positive correlation between stream power, bed shear stress and bedload transport rates has been clearly shown by previous empirical studies of loose-bed channels. It is proposed that large-scale patterns of erosion and deposition in alluvial basins result from downstream changes in bedload transport rates, produced by the observed trends in these two parameters. If this proposal is to be fully tested, further work is needed to assess the affects of downstream fining of bed material, short-term fluctuations in discharge and downstream exchange of particles between the suspended load and bedload.

Sediment transport analysed by energy derived concepts

Abstract: The sediment transport in natural rivers may be estimated on the basis of the stream power concept. The rate of energy dissipation derives from an energy balance which adjusts to the river bed's roughness, sediment discharge, channel geometry and cross section. Under these assumptions the sediment transport is analysed under various flow conditions as well as changing turbulent kinetic energy. It is shown and discussed under what assumptions the concept of energy dissipation rate for sediment transport can be extended from steady open-channel ow to unsteady flow conditions.

Modelling suspended sediment supply to the River Rhine drainage network: a methodological study.

Abstract: In the framework of a climate change research project, an approach and preliminary results are presented of modelling the suspended sediment supply to the drainage network of the River Rhine. Concepts of the GAMES model are used as a basis. In the model, the amount of mobilized sediment that actually reaches the stream network depends on the proximity of the sediment source to the stream, the occurrence of overland flow and on the character of the terrain along the route towards the channel (including surface roughness and slope angle). Attention is paid to problems that are specific to the large size of the studied basin and the spatial resolution of the available data set. Preliminary results show that estimates of sediment supply from hillslope to streams are reasonable. Calculated sediment supply was compared with measured sediment yields at several sampling stations in the Rhine basin. It appeared that suspended sediment supplied in lower parts of the basin is transported more effectively through the alluvial system. A large part of the sediment produced in the Alps and in the Swiss middle mountains is stored in the alluvial system further downstream where stream power decreases.