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Flow over stepped weirs are characterized by their strong turbulent mixing which enhances the oxygen transfer and dissolved oxygen (DO). This paper investigates the aeration performance of stepped weirs, and in particular, the effects of installation of the labyrinths on the steps, various weir slopes, upstream DO concentrations and tailwater depths. 19 physical models of flat, stepped-labyrinth and pooled-stepped weirs with three different slopes (1:1, 1:2 and 1:3 V: H) were tested. For each configuration, the downstream concentration of DO was measured utilizing a wide range of upstream concentrations of DO. The results indicated that the DO ratio with the best configurations were the stepped-labyrinth weirs with slopes of 1:1 and 1:2; approximately 62% higher than that of the flat stepped weirs. However, the dissolved oxygen efficiency showed a 15% decrease in models with a slope of 1:3 compared to those with a slope of 1:1. In all cases, the results demonstrated that the dissolved oxygen efficiency decreased either by increasing the upstream DO concentration or by increasing the flow discharge. The results yielded new design criteria for flat and stepped-labyrinth weirs to attain maximum aeration performance. Finally, empirical correlations were proposed for predicting the DO over stepped-labyrinth weirs. [ABSTRACT FROM AUTHOR]

Experiments were performed for local scour at a complex pier with two inclined, rectangular columns footed on a group of circular piles with a pile cap. The research fills a gap in existing literature, where studies for complex piers have considered a single, vertical column. The laboratory campaign involved the variation of the pile diameter and arrangement, and of the cap thickness and elevation above the non-scoured bed. The results of carefully conducted scour runs revealed the cap elevation as a most influential parameter. In cases of buried and partially buried pile cap, in fact, the cap acted as a scour countermeasure. For high cap elevation, the supporting piles were also exposed to the flow and their size influenced the resulting scour depth values as it directly impacted on the pier frontal area. The measured scour depth was compared to the values predicted by several literature methods for complex piers with a vertical column, supporting the possibility to extend their use to the geometry investigated in the present study. [ABSTRACT FROM AUTHOR]

River bridge piers may collapse due to the local scour around their foundations. It is known that local scour is an effect of the three-dimensional flow field that develops near the pier and that the geometric complexity of a non-cylindrical pier may, correspondingly, increase the complexity of the process. It is also known that various devices may be used as scour countermeasures. This manuscript explores the use of a bed sill as a countermeasure for local scour at a complex bridge pier compound of an array of piles, a pile cap, and two inclined columns with the rectangular sections above the cap. This pier geometry, never studied before in combination with a scour countermeasure, was stimulated by an existing bridge. Different sill placements were tested (at the upstream or downstream edges of the pier, or in an intermediate position) for various values of the pile diameter and number, cap thickness and cap elevation. The results of a wide experimental campaign consistently showed that the most effective placement of the transverse sill was at the upstream edge of the pier, for which scour reductions of up to 30–40% could be obtained for the long-term scour depth. The countermeasure performance decreased to about 10% when the sill was placed at the downstream edge of the pier. Furthermore, the installation of a transverse sill upstream of the pier also changed the shape of the scour hole because the pier was then located in an area prone to sill scour; however, for the present experiments, the combination of the effects was beneficial in terms of the resulting scour depth. Although the investigation of a single hydro-dynamic condition prevents the experimental findings from being generalized, the promising results stimulate further consideration of a transverse sill as a countermeasure for local scour at a complex pier. [ABSTRACT FROM AUTHOR]

For a given width, a labyrinth weir has a developed crest length, thereby increasing the flow capacity for a given upstream headwater. This paper experimentally studies the flow over labyrinth weirs with semicircular and sinusoidal configurations in a rectangular channel under a wide range of flow discharges. The effects of headwater ratio (HT/P), length of weir (L/P), arc radius ratio (R/P) and the number of cycles (N) on the discharge coefficient of semicircular and sinusoidal labyrinth weirs are investigated. Experimental results indicated the decreasing trend of Cd for HT/P>0.35 which is probably related to the progressive development of local submergence. Despite the effects of local submergence, the labyrinth weirs have nearly the same discharge coefficient as broad-crested weirs, and the flow discharge exceeded the linear weirs efficiency by ∼30. Additionally, reliable equations for estimating the discharge coefficient of labyrinth weirs with semicircular and sinusoidal configurations are presented. [ABSTRACT FROM AUTHOR]

In this study, the effects of geometric parameters, such as the ramp roughness size and the ramp slope on the scour parameters downstream of block ramps, are experimentally investigated for different hydraulic conditions. Scour parameters, such as the maximum scour depth and length and the maximum ridge height and length, are evaluated. Experiments are conducted in clear water conditions (no sediment transport) for different gravel ramp slopes in which different critical flow depths and tailwater depths are examined. The results indicate that the maximum scour depth downstream of a block ramp for different bottom slopes is directly affected by the tailwater depth, independent of the critical flow depth; the scour depth decreases by increasing tailwater depth. A comparison of the results indicates that increasing the roughness of the block ramp leads to a reduction in the maximum scour depth. [ABSTRACT FROM AUTHOR]

Grade control structures are commonly used to prevent degradation, increase bank and bed of rivers stability and prevent cross structures failure in rivers. To safe design grade control structures, estimation of local scour depth downstream of these structures is crucial. In this study, the effects of different parameters on local scour at the downstream of grade control structures with labyrinth planform were investigated experimentally. Different types of rectangular and trapezoidal labyrinth planform weirs were studied. Experimental results showed that the labyrinth planform has a high effect on reducing scour depth. It was found that decreasing the length of cycles in the trapezoidal labyrinth weirs and increasing width of cycles in rectangular weirs causes reduction of the maximum scour depth. Experimental observations and comparison of results showed that trapezoidal labyrinth weirs effectively reduce scouring with an average of 19 percent in comparison with linear weir; moreover, the rectangular labyrinth weir reduces to 10 percent. Furthermore, dimensional equation for prediction of scour depth is derived. [ABSTRACT FROM AUTHOR]