1,721,092 research outputs found
Dimensions of standing waves at steps in mountain rivers
No full textOscillations of the water surface are common features of flows around critical
conditions (Fr near 1) and of both natural and structure-induced undular hydraulic jumps.
The paper describes experimental tests and field data on the dimensions of standing waves
created by artificial drops in steep gravel bed rivers. The purpose of the research is to
analyze what parameters affect the phenomenon, to provide semiempirical formulations
for wave dimensions, and to assess whether previous models for undular hydraulic jumps
and antidunes are reasonably predictive. The dimensionless wavelength and wave
amplitude were correlated to the Froude number at the sill. The first wavelength
appears linearly related to the Froude parameter, whereas the amplitude of the first wave
shows a less defined behavior, possibly indicating that a maximum value occurs for sill
Froude numbers around 1.6–1.7. The corresponding wave steepness (i.e., wave
amplitude/length) results between 0.15–0.16, and this range also characterizes the point at
which the dimensionless trough depth below the sill achieves a local maximum, probably
related to hydrodynamic conditions just before wave breaking. The transition between
roller and undular jumps at drops is then argued to likely represent a critical stage in
step pool streams, and the hydraulic and morphological implications of this finding are
also discussed, with particular emphasis on step stability and step wavelength
Effect of sill spacing and sediment size grading on scouring at grade-control structures
No full textSequences of artificial steps are sometimes used to reproduce the natural step–pool morphology of high-gradient streams.
The depth, length and shape of the scour holes in gravel-bed rivers can be predicted reasonably using recently developed
formulae. However, the properties of the scour holes can sometimes be affected by the distance between structures. This
effect is called ‘geometrical interference’ and leads to a reduction of the scour hole compared to its potential size. Geometrical
interference may occur in sequences of artificial steps in high-gradient torrents, where structures are sometimes built at
distances of a few tens of metres apart, but may also apply to natural step–pool systems. In this paper, a series of tests have
been conducted to determine the effect of bed sill spacing and sediment grading on the potential erosion by jets forming over
the sills. A new formula is derived, applicable to high-gradient streams (slope > 0·04), which can be applied to the special
case of scour holes developed by interfering sills. Sediment size gradation, not accounted for in previous formulae, is found
to have a significant effect on the scour dimensions and is included in the new predictive formula
Bedload dynamics in steep mountain rivers: Insights from the Rio Cordon experimental station (Italian Alps)
No full text
Interanual variation of suspended sediment load and sediment yield in an alpine catchment
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