Sevket Cokgor

Reservoir sedimentation reduces storage in hydropower facilities and threatens turbine integrity through sediment entrainment at turbine intakes. Pressurized sediment passages are utilized as countermeasures; however, their performance in reservoirs with irregular topographies is not well documented. This study reports the flow dynamics and sediment flushing in a 1/30 scale physical model of a dam. Three-dimensional velocity components were recorded using a Nortek Acoustic Doppler Velocimeter at 240 points across five elevations upstream of the sediment passage entrance. Reynolds stresses, bed shear stresses, and Shields parameters were derived from the data. The highest turbulent shear stress, over 12 Pa, was observed in front of the passage inlet. The Shields parameter values exceeded the 0.045–0.06 critical range, consistent with bed-load motion during flushing. Approach velocities above 1 m/s were confined to approximately 30 m upstream of the passage entrance, defining a finite influence radius. The measured flushing cone length and volume agreed within 4% with prior experimental data on flushing cones, although the scoured area geometry was asymmetric due to the passage offset. Lowering the reservoir from 1147 to 1133 m at the spillway-crest-level increased the flushed volume by only approximately 6%, whereas the near-inlet velocity field changed little between the two cases; the local velocity gradient at the passage entrance, rather than the reservoir level itself, governed the flushing efficiency.

Thermal discharge from power plants causes significant concerns in aquatic environments. The purpose of this study is to evaluate how river mouth morphodynamics, particularly spit development and removal, influence the dispersion of thermal plumes. To achieve this, a case study was carried out at a coastal power plant in southwest Türkiye, where thermal effluent is conveyed to the sea through a low-flow river. Field measurements combined with numerical modeling were used to analyze plume dynamics under varying spit configurations. Results revealed that the evolution of a spit on one side of the river mouth influences plume dispersion and redirects the mixing zone toward the opposite shoreline. Numerical simulations demonstrated that spit development reduces dispersion efficiency (by over 75%), while the physical removal of the spit significantly improves it, reducing temperature excess from 4–5 °C to 0–1 °C within the mixing zone, meeting safe environmental standards. The findings highlight the pivotal role of morphological changes in governing thermal discharge behavior and emphasize the importance of continuous monitoring and management strategies, such as periodic dredging, to ensure compliance with environmental regulations.

The literature suggests two forms of flow slides: breaching and liquefaction. Both forms of failure have comparable ultimate circumstances, but the progression and sand movement mechanisms of breaching failure diverge from those of liquefaction. The first type, breaching, occurs in densely packed sand and is characterized by slow sand grain discharge throughout the dilation of the failing soil particles and negative excess pore pressures. The latter form, known as liquefaction, is the process by which a mass of soil abruptly begins to behave like a flowing liquid, and as a result, it can flow out across overly mild slopes. The process begins in compacted sand and is linked to positive surplus pore water pressures that are caused by the compaction of the sand. Despite the available literature on flow slide failures, our understanding of the mechanisms involved remains limited. Since flow slides often begin below the water surface, they can go undetected until the collapse reaches the bank above ground. The complexity of flow slides requires the use of cutting-edge technological instruments, diving equipment, advanced risk assessment, and a variety of noteworthy probabilistic and sensitivity analyses. Hence, we developed a new sensitivity index to identify the risk of breach failure and vulnerable coastal areas to this risk. In addition, we developed a sophisticated hybrid model that allows for all possibilities of flow slides in sync with random variables used in this new sensitivity index. In this new hybrid model, three distinctive models exist. The 3D Hydrodynamic Model addresses waves, wind, current, climate change, and sediment transport. The Monte Carlo Simulation is responsible for sensitivity analysis, and the Bayesian Network focuses on joint probabilities of coastal flow slide parameters of this new index that incorporates all environmental parameters, including climate change. With the assistance of these three models, researchers aim to: (a) expand the application scope by presenting a method on coastal flow slides; (b) consider different particle diameters corresponding to critical angle slope failure; (c) analyze variables that can play a pivotal role in the flow slides; and (d) present a methodology for coupling coastal flow slide projections with reliable outcomes. The hybrid model incorporates random variables of retrogressive breach failures, and the new risk index considers their ranges to control the simulation. The use of such a hybrid model and risk index offers a robust and computationally efficient approach to evaluating coastal flow slides.

In this experimental study, the boulder-flow interaction associated with the self-aeration process was investigated in a 0.50m wide flume. Experiments were performed with three different boulder arrangements and four different relative boulder submergences using Reynolds numbers from 5×103to 5 × 104. A boulder-flow interaction can trigger air–water mass transfer by generating turbulence, a hydraulic jump and plunging jet flow. When the boulders are submerged by the water, the maximum local aeration efficiency tends to decrease rapidly as does the flow resistance. Furthermore, the maximum local aeration efficiency is positively related to the blockage ratio of the boulder(s). The blockage ratio appears to represent the head loss, suggesting a possible interrelation between the aeration efficiency and the energy dissipation