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Boes, Robert M.
- Conference Paper
Large wood (LW) transport can highly increase during flood events, leading to accumulations at river infrastructures like bridges or weirs. To mitigate the potential flood hazard, retention racks are common methods to retain LW upstream of endangered settlements. To improve the design of these racks, knowledge on both backwater rise and local scour is deemed necessary. The majority of LW retention racks are vertical in cross-section and, therefore, disrupt sediment continuity. We hypothesize that the inclination of LW retention racks reduces backwater rise and sediment disruption. A series of flume experiments was conducted to analyze backwater rise and local scour as a function of (1) rack inclination, (2) hydraulic inflow condition, (3) uniform bed material, and (4) LW volume (Figure 1). To estimate local scour solely due to LW accumulations, the initial bed shear stress was set below the critical bed shear stress for incipient motion. To model a LW accumulation, a maximum solid LW volume Vs = 23 dm3 was added in 5-10% packages to the flow. The respective backwater rise and local scour were measured after the addition of each LW package. The results showed that backwater rise decreases with decreasing rack inclination angle to the horizontal. LW predominantly accumulated at the upper part of the rack, leading to an open flow cross-section below the accumulation. The resulting local scour further increased the open flow cross-section. The results were combined in design equations to estimate backwater rise and local scour, and enable an improved design of LW retention racks. Future model tests will include sediment feeding to further evaluate sediment continuity Show more
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Organisational unit03820 - Boes, Robert / Boes, Robert
NotesConference lecture on January 9, 2019.
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