ASCE Manual 54 , Sedimentation Engineering, prepared under the leadership of Professor Vito A. Vanoni, has provided guidance to theoreticians and practitioners’ world wide on the primary topic of sediment problems involved in the development, use, and conservation of water and land resources. First published in 1975, Manual 54 gives an understanding of the nature and scope of sedimentation problems, of the methods for their investigation, and of practical approaches to their solution. It is essentially a textbook on sedimentation engineering, as its title accurately refl ects. Manual 5 4 was the fi rst and most comprehensive text of its kind and has been circulated throughout the world for the past 30 years as the most complete reference on sedimentation engineering in the world. It has recently been published again as the Classic Edition (Vanoni 2006). In the spirit of its predecessor, this chapter of Manual of Practice 110 , Sedimentation Engineering, aims at presenting the state of the art concerning the hydraulics of sediment transport in fl uvial systems based on the knowledge gained in the last three decades. A concerted effort is made to relate the mechanics of sediment transport in rivers and by turbidity currents to the morphodynamics of lake and reservoir sedimentation, including the formation of fl uvial deltas.

Sediment Transport and Morphodynamics

Concentrations in oscillatory sheet flow for well sorted and graded sands

[1] U‐tube measurements of instantaneous velocities, concentrations, and fluxes for a well‐sorted, medium‐sized sand in oscillatory sheet flow are analyzed. The experiments involved two velocity‐asymmetric flows, the same two flows with an opposing current of 0.4 m/s, and a mixed skewed‐asymmetric flow, all with a velocity amplitude of 1.2 m/s and flow period of 7 s. We find that the net positive transport rate beneath velocity‐ asymmetric oscillatory flow results from large, but opposing sand fluxes during the positive and negative flow phase. With an increase in velocity asymmetry and, in particular, velocity skewness, the difference in the magnitude of the fluxes in the two half cycles increases, leading to larger net transport rates. This trend is consistent with the observed increase in skewness of the oscillatory bed shear stress. Phase‐lag effects, whereby sand stirred during the negative flow phase has not settled by the time of the negative‐to‐positive flow reversal and is subsequently transported during the positive flow phase, are notable but of minor importance to the net transport rate compared to earlier experiments with finer sands. In the vertical, the oscillatory flux is positive above the no‐ flow bed. Within the sheet flow pick‐up layer, the oscillatory flux is negative and similar in magnitude to the positive flux induced by the residual flow. The 0.4 m/s opposing current causes more sand to be picked up during the negative than during the positive flow phase. Above the no‐flow bed the resulting negative oscillatory flux is comparable in magnitude to the current‐related flux.

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Observations of velocities, sand concentrations, and fluxes under velocity-asymmetric oscillatory flows

Flow tunnel measurements of velocities and sand flux in oscillatory sheet flow for well-sorted and graded sands

http://www.geosci.usyd.edu.au/users/hughes/baldock_etal_2004.pdf

Settling velocity of sediments at high concentrations

Experiments on sand transport have been carried out in the Sloping Sediment Duct at HR Wallingford. The aim of the experiments was to investigate sediment transport mechanisms, for sand of varying degree of grading, on sloping beds. The Sloping Sediment Duct is a steady flow, recirculating duct, capable of generating mean flow speeds of up to 1 m/s and tilting to +/-30°. Twenty-two tests with two different sediments were conducted. Both sediments had a median grain size of about 0.23 mm but different standard deviations. Bed slopes up to +/-20° were used in the experiments. The results show that bedforms have a significant effect on the transport rate. Since the bedforms, in turn, are affected significantly by the slope, the relation between transport rate and slope is not a monotonic function. Maximum suspended transport rates were attained for downslope flows at angles of about 10°. The transport rate for widely graded sediment was significantly larger than that for well-sorted sediment for almost all flows and slopes.

Sand transport on steeply sloping plane and rippled beds

Graded sediments in oscillatory sheet-flow

Measurements of concentrations and suspended sediment sizes above well-sorted and mixed sand beds in sinusoidal flows in a large oscillatory flow tunnel are presented. The results show that sediment grading is fundamentally important to the entrainment and suspension of sand from the bed. The depth of bed mobilised by the flow depends on the proportion of coarse sand in the bed, with a greater proportion of coarse sand resulting in a smaller mobilised depth. The distribution of the mobilised sand above the bed strongly depends on the grading. Sand is suspended to higher elevations when the proportion of fine sand is greater. Conversely, a lower proportion of fine sand leads to lower suspended sand concentrations high above the bed and higher concentrations within the sheet flow layer. These observations are intuitively sensible: the experimental results provide quantitative measures of the observations.

Scott Wright

Papers

Concentrations in oscillatory sheet flow for well sorted and graded sands

Flow tunnel measurements of velocities and sand flux in oscillatory sheet flow for well-sorted and graded sands

Sand transport on steeply sloping plane and rippled beds

Graded sediments in oscillatory sheet-flow

Experimental Study of Graded Sediments in Sinusoidal Oscillatory Flow