Fluvial solid transport determines the solid flow rate by bedload in a free-surface flow. The approach used is the deterministic one based on relationships between dependent and independent variables and on the evaluation of the conditions of incipient motion, expressed as the excess of a fixed quantity with respect to its critical value.
The output provides a report summarizing the relationships used and the calculation results.
For desktop applications for hydrology and hydraulics visit: geostru.eu/idraulica. For details, see the video…
The critical conditions are defined by functional relationships obtained by making the following basic assumptions:
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channel with a horizontal bed;
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high submergence (the flow totally submerges the sediments), which occurs for h > 6d;
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homogeneous bed material with the absence of cohesive forces between particles;
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absence of material along the banks of the riverbed.
Depending on the chosen author, the application allows the removal of the basic assumptions by considering appropriate corrective factors chosen by the user.
More information on solid transport
In the calculation of free-surface flows, the geometry of the channel (planimetry, altimetry, cross-sections) is usually considered as an input data of the problem, known on the basis of topographic surveys. Indeed, in the general case where the channel is excavated in non-cohesive material, the geometry cannot be considered a priori fixed over time, due to the phenomena of erosion and deposition of the constituent material of the bed and banks, moved by the flow. Under the action of hydrodynamic thrusts, in fact, the solid grains can be set in motion and transported downstream; furthermore, the phenomenon of bedload transport, in which the grains move on the bottom with rotary and/or sliding motions, more or less intermittently, differs from the phenomenon of suspended transport, in which the solid travels long distances dragged within the current, and integral to it.
As a consequence of the described processes, the riverbed of a watercourse can undergo progressive changes over time, in relation to its planimetric characteristics, and therefore to its path, altimetric characteristics (slopes), the shape of the cross-sections, and the particle size distribution of the bed material, to which the roughness values are linked. Riverbed modifications can be the consequence of time-limited events (floods, inundations), or the normal regime of the watercourse: in any case, once the evolutionary transient is over, static equilibrium situations can occur, in which solid transport phenomena are absent, or dynamic equilibrium between erosion and deposition of the moved material.
It is also appropriate to distinguish distributed phenomena, which involve the entire cross-section of the riverbed over longitudinally extended stretches, from concentrated phenomena, limited to specific areas of the cross-section, or to limited stretches of the riverbed, and linked to the presence of geometric singularities in the watercourse (curves, hydraulic structures, …). In the following, mainly distributed phenomena will be considered, only mentioning concentrated ones in a final paragraph.