Driftwood, while a natural part of the riverine ecosystem, can alter its flow and affect hydraulic characteristics. Flooding can exacerbate the issue, leading to driftwood-loaded rivers, and large trunks that block, accumulate, or reduce flow around bridge piers, weirs, and culverts, which can be particularly risky near dam spillways. On the flip side, wood helps improve aquatic habitats downstream, by providing spaces for animals to hide. Traditional approaches for dealing with driftwood have included maintenance of vegetation along the banks of waterways, removal of the driftwood, and using transfer structures to create passageways. Most studies have focused on the removal of driftwood to prevent clogging, and not on potential ecological benefits downstream.
Can we both minimize clogging and provide downstream benefits? Researchers Loïc Bénet, Giovanni De Cesare, and Michael Pfister explored this challenge of dam safety and the passage of driftwood in their study, “Partial Driftwood Rack at Gated Ogee Crest: Trapping Rate and Discharge Efficiency” in the Journal of Hydraulic Engineering. They experimented with a novel partial rack that would enable driftwood to pivot and pass downstream. Learn more about their research at https://doi.org/10.1061/(ASCE)HY.1943-7900.0001994. The abstract is below.
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.
Read the full paper in the ASCE Library at https://doi.org/10.1061/(ASCE)HY.1943-7900.0001994