https://orcid.org/0000-0002-4602-0758
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ABSTRACT
River infrastructures like bridges are prone to accumulations of transported large wood (LW) during floods. To contribute to an improved risk evaluation, the prediction of LW accumulation probability (AP) is crucial. Previous studies on LW AP focused mainly on the influence of a bridge deck. In the present study, flume experiments were conducted to investigate LW AP at bridge piers with special emphasis on (1) approach flow conditions, (2) bridge pier characteristics with different pier roughness, shape, diameter, and pier number, (3) LW characteristics, involving various log lengths, log diameter, log density, LW with and without branches, and uncongested versus (semi-) congested LW transport, and (4) channel bed, i.e. scour. Based on the experiments, AP is mainly a function of approach flow velocity and log length. The results were combined in a design equation to predict AP for risk assessment in engineering application.
Notation
| Apr | = | projected area (m2) |
| B | = | width (m) |
| Cd | = | drag coefficient (−) |
| di | = | grain size diameter at which i% of the sample is finer (m) |
| dL | = | log diameter (m) |
| dLm | = | mean log diameter (m) |
| dm | = | mean grain size diameter (mm) |
| dP | = | pier diameter (m) |
| D | = | deposition height (m) |
| Dmax | = | maximum deposition height (m) |
| F | = | Froude number (–) |
| Fo | = | approach flow Froude number (–) |
| F | = | hydraulic force (N) |
| Ffriction | = | friction force (N) |
| F|| | = | parallel force (N) |
| FN | = | normal force (N) |
| g | = | gravitational acceleration (m s−2) |
| h | = | flow depth (m) |
| hb | = | height of movable bed (m) |
| ho | = | approach flow depth (m) |
| ho/HBridge | = | relative approach flow depth (–) |
| HBridge | = | clearance height at the bridge (m) |
| Jo | = | bottom slope (–) |
| kSt | = | channel roughness (m1/3 s−1) |
| Lb | = | length of movable bed (m) |
| LL | = | log length (m) |
| LWP | = | large wood probability factor (–) |
| N | = | number of repetitions (–) |
| Nreq | = | number of required repetitions (–) |
| p | = | accumulation probability (–) |
| pmax | = | maximum accumulation probability (–) |
| Q | = | discharge (m3 s−1) |
| R | = | Reynolds number (–) |
| Rh | = | hydraulic radius (m) |
| S | = | scour depth (m) |
| Smax | = | maximum scour depth (m) |
| tW | = | watering time of wood (s) |
| v | = | flow velocity (m s−1) |
| vo | = | approach flow velocity (m s−1) |
| γ | = | log position angle (°) |
| γcr | = | critical log position angle (°) |
| γIC | = | initial log position angle (°) |
| θ | = | non-dimensional bed shear stress (–) |
| θcr | = | critical non-dimensional bed shear stress (–) |
| λ | = | scale factor (–) |
| μ | = | friction coefficient (−) |
| ν | = | kinematic viscosity (m2 s−1) |
| Πn–r | = | non-dimensional parameters of Π-theorem (–) |
| ρL | = | density of logs (kg m−3) |
| ρW | = | density of water (kg m−3) |
| σ | = | water surface tension (kg s−2) |