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ABSTRACTExperiments 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.

ABSTRACTFor 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 Cdfor 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.

ABSTRACTGrade 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.