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Résumé

Numerical simulations documented in literature and experiences with driftwood blockage suggested that the flow field upstream of Piano Key Weirs (PKWs) includes an active zone reaching far down near of the weir. In other words, a pronounced vertical upwards-oriented flow active along the weir front presumably occurs, in contrast to a standard overfall. An extended flow field is related to relatively low velocities with a reduced particle transport capacity. This capacity is of interest for sedimentation basins (settling tanks) of wastewater treatment plants. If the particle re-suspension capacity is reduced under similar unit discharges, then either the basin volume can be lessened or the efficiency of the basin augments for the same volume. The paper presents preliminary numerical simulations of the flow velocity distribution in sedimentation basins near both, a sharp-crested weir and a PKW as overfall. Further, some preliminary physical model tests are presented, giving indications about the re-suspension potential of particles, as a function of their vicinity to the weir crest and the unit discharge.

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