Gökçen Bombar

Experimental Study of the Coarse Surface Development Effect on the Bimodal Bed-Load Transport under Unsteady Flow Conditions

AbstractGravel-bed rivers display a surface layer that is coarser than the substrate lining below this armored surface. The armored layer that is developed under certain flow conditions may be attributed as water-worked sediment bed. Both the threshold of incipient motion and the bed-load transport are affected by the presence of this layer. In this study, the coarse surface development and its effect on the sediment transport were investigated experimentally in a rectangular flume. Four antecedent flow rates were combined with an input hydrograph, without sediment feeding. The reference shear stress of individual fractions and the grain-size distribution were determined after the development of the coarse surface due to the antecedent flow. Then a triangular-shaped hydrograph was generated for both the intact surface and the coarse surface cases. It was seen that the maximum bed-load transport values obtained in unsteady flow experiments were highly dependent on the coarse surface formed by the anteceden...

Study of the time-dependent clear water scour around circular bridge piers

Abstract The local scour around bridge piers influences their stabilities and plays a key role in the bridge failures. The estimation of the maximum possible scour depth around bridge piers is an important step in the design of the bridge pier foundations. In this study, the temporal evolution of local scour depths as well as the equilibrium scour depths were analyzed. The experiments were carried out in a rectangular flume by using uniform sediment with median diameter of 3.5 mm and geometric standard deviation of 1.4. The diameters of the tested circular bridge piers were 40 mm, 80 mm, 150 mm and 200 mm. The flow and scour depths were determined by ultrasonic sensors. The experiments were realized in clear water conditions with various constant flow rates. The experimental findings were compared with those calculated from some empirical equations existing in the literature. A new empirical relation involving the flow intensity, the relative water depth and the dimensionless time is also introduced. The advantage of this proposed relation is that the only parameter requiring the calculation is the critical velocity, other parameters being known geometric and hydraulic parameters. The performance of this relation was tested by using experimental data available in the literature, and a satisfactory compatibility was revealed between the experimental and numerical results.

Environmental impacts and impact mitigation plans for desalination facilities

AbstractA number of sea water desalination technologies have been developed during the last several decades. Although these techniques are promising options for freshwater augmentation in coastal establishments and islands, they may have certain impacts to the environment. To safeguard a sustainable use of desalination technology, the impacts of the desalination facility should be identified and mitigated by means of an environmental impact assessment study as well as by environmental management plans (EMPs). The EMP should include tables answering questions like who is responsible from “what” and “when” and, “which” precautions will be taken and “where” these precautions should be implemented. This study aims to analyze the potential environmental impacts of desalination plants and propose measures mitigating their negative impacts. In the article, components of a desalination system, i.e. open intake, pretreatment, membrane desalination system, outfall with diffuser, and transfer pipeline, are identifie...