The computation of temporal variation of clear-water scour is important for the design of bridge foundations. Previous studies implied that a very long flow duration is needed to achieve equilibrium scour at bridge abutments. However, the corresponding durations in the prototype conditions may yield considerably greater values than the time to peak of most of the design floods of small to medium sized catchment basins. Therefore, there is a need to estimate the temporal variation of scour depth. This study deals with development of a semi-empirical model for determining the time-dependent variation of clear-water scour depth at vertical-wall abutments. This approach applies the sediment continuity equation to a scour hole around a vertical-wall abutment. A sediment pickup function was used to formulate the rate of sediment transport from the scour hole. The results of the proposed model were compared with those of empirical models. The model agreed well with the test results. RÉSUMÉLe calcul de la variation temporelle de l'affouillement en eau claire est important pour la conception des fondations de pont. Les études précédentes supposaient qu'une durée très longue d'écoulement est nécessaire pour atteindre l'équilibre des affouillements aux butées de pont. Cependant, les durées correspondantes, dans les conditions de prototype peuvent indiquer des valeurs considérablement plus grandes que le temps mis pour atteindre le maximum de la plupart des crues nominales des bassins versants petits et moyens. Par conséquent, on a besoin d'estimer la variation temporelle de la profondeur d'affouillement. Cette étude développe un modèle semi-empirique permettant de déterminer l'évolution en fonction du temps de la profondeur d'affouillement en eau claire aux butées de murs verticaux. Cette approche applique l'équation de continuité du sédiment à un trou d'affouillement autour d'une butée. Une fonction de collecte de sédiment a été utilisée pour exprimer le taux de transport des sédiments issus du trou. Les résultats du modèle proposé ont été comparés à ceux des modèles empiriques. Le modèle était bien conforme aux résultats d'essai.
Accurate estimation of the maximum possible depth of scour at bridge abutments is important in decision-making for the safe depth of burial of footings. Besides, investigation of the geometric features of scour holes around abutments provides useful information for the degree of scour counter-measure to be implemented against excessive scouring. Experiments have been performed to investigate time-dependent characteristics of scour holes around vertical wall abutments under clear water conditions with uniform bed materials. Temporal variations of scour depth and scour contours were measured. Using this information, an empirical relation was developed for temporal variation of scour depth. Additional relations were also derived for time-dependent volume and surface area of the scour holes around abutments. The findings of this study may provide useful information for preliminary design of abutment footings and placement details of armoring counter-measures, such as riprap.
Turbulence statistics are measured in a shallow stream Effects of turbulent kinetic energy on the dissolved oxygen transfer is investigated Figure A. Variation in dissolved oxygen with kinetic energy Purpose: This study attempts to obtain as much data as possible very close to the bed. Using the data distribution of turbulence intensity, the Reynolds stresses for the three velocity components, integral time scales, integral length scales, and turbulence kinetic energies are calculated, interpreted along the water depth and around a boulder. Effect of turbulent kinetic energy on the dissolved oxygen concentration is investigated. Theory and Methods: Measurements are conducted at the centre of a mountainous shallow river called the Melendiz River, located close to Aksaray City, Turkey.. A ruler is attached into the frame to allow adjustment of the ADV in all directions at the millimetre sensitivity. The distance from the bed is checked in two ways, namely using the distance sensor of the ADV and a ruler. During the experiments, the data is sampled at a constant 100 Hz rate. Results: According to the autocorrelation function results, the points close to the wake region exhibit high dependence. The spectral analysis shows that the majority of the turbulence kinetic energy is concentrated in high-period (low-frequency) structures (circulations and eddies). The spectral density plots were obtained for the downstream and upstream faces of the boulder. The spectral density graphs obtained from points very close to the bed contain more noise than those of the higher points. A-1 slope is clearly observed before the-5/3 slope of the inertial sub-range. Conclusion: The distribution of turbulent kinetic energy was obtained and it is seen that TKE suddenly increases from a point very close to the bed, reaches its maximum at relative depth of 0.4, and then decreases in a fluctuating trend The relationship between the turbulent kinetic energy and dissolved oxygen concentration was investigated and there is a high correlation between these two parameters.
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