Partial Driftwood Rack at Gated Ogee Crest: Trapping Rate and Discharge Efficiency

Abstract

Driftwood belongs to natural rivers just like water and sediment do. A sound ecosystem requires driftwood, although it might jam at civil structures, altering the flow section and rise the backwater. Safety considerations suggest removing wood from rivers, whereas ecological experience asks for its presence. The situation might become critical if spillways clog during floods, so that their discharge capacity reduces. For narrow bays, full racks mounted upstream of the weir or overhanging piers trap the driftwood distant from the flow control section. The hydraulic capacity is then maintained, but the driftwood has to be removed after the event. We thus investigated herein with a physical model a novel partial rack, motivating the driftwood for uncongested appearance to partially pivot and pass, but ensuring a high discharge capacity under hypercongested appearance. The partial rack configuration was specified, together with the related trapping rate and discharge efficiency.