In this study, the full Launder, Reece and Rodi pressure-strain model and nonlinear boundary damping functions were incorporated in OpenFOAM® to simulate the turbulence-driven secondary currents in supercritical narrow channel flows such as in sediment bypass tunnels (SBTs). Five simulations were performed under uniform flow conditions covering Froude numbers from 1.69 - 2.56 and aspect ratios (channel width to flow depth) a_r from 0.9 - 1.91 to investigate the formation of secondary currents and their impacts on longitudinal velocity, turbulence characteristics, and bed shear stress distribution. The numerical results of the maximum longitudinal velocity and the average shear velocity show marginal deviations, of less than 2.6%, from two-dimensional experimental results acquired under decelerating flow conditions. However, some differences are observed for the secondary currents and for the vertical turbulence intensity and Reynolds shear stress in the outer flow region, especially for cases with higher flow nonuniformity (that can influence the surface perturbation) whose influence is missing in the numerical model. No intermediate vortex is observed for a_r = 1.91. However, it develops for lower a_r, and detaches from the free surface vortex when a_r {less than or equal to} 1.05. Such vortex bulges the longitudinal velocity contour lines inward and the zone of higher longitudinal velocity narrows and deepens with a decrease in a_r. The decrement reduces the magnitude of the normalized maximum secondary velocity. It also affects the bottom vortex which alters the bed shear stress distribution.

Energy storage through hydropower leads to free surface water waves in the connected reservoirs. The reason for this is the movement of water between reservoirs at different elevations, which is necessary for electrical energy storage. Currently, the expansion of renewable energies requires the development of fast and flexible energy storage systems, of which classical pumped storage plants are the only technically proven and cost-effective technology and are the most used. Instead of classical pumped storage plants, where reservoirs are located on the surface, underground pumped storage plants with subsurface reservoirs could be an alternative. They are independent of topography and have a low surface area requirement. This can be a great advantage for energy storage expansion in case of environmental issues, residents’ concerns and an unusable terrain surface. However, the reservoirs of underground pumped storage plants differ in design from classical ones for stability and space reasons. The hydraulic design is essential to ensure their satisfactory hydraulic performance. The paper presents a hybrid model study, which is defined here as a combination of physical and numerical modelling to use the advantages and to compensate for the disadvantages of the respective methods. It shows the analysis of waves in ventilated underground reservoir systems with a great length to height ratio, considering new operational aspects from energy supply systems with a great percentage of renewable energies. The multifaceted and narrow design of the reservoirs leads to complex free surface flows; for example, undular and breaking bores arise. The results show excessive wave heights through wave reflections, caused by the impermeable reservoir boundaries. Hence, their knowledge is essential for a successful operational and constructive design of the reservoirs.

The present study documents the successful application of a Reynolds-averaged Navier-Stokes model with conventional turbulence closure to calculate discharge coefficients for submerged flow conditions at ogee-type weirs. The flow pattern downstream of submerged weirs is complex. At low submergence, there is a plunging jet and submerged hydraulic jump. At higher levels of submergence, the jet detaches from downstream of the crest and develops toward the free water surface. The results presented are of particular interest to the hydraulic engineer because they demonstrate that reliable results for the complex flow problem are achieved, but only with the use of a fine computational mesh. It is well known that the results of computational fluid dynamics (CFD) models are strongly mesh dependent, but extensive sensitivity analysis is often time-consuming and costly. Therefore, engineering practice relies on cases that have been tested extensively. For the mesh resolution, the present study recommends a nondimensional number that can be used as a reference for modeling flow over weirs. An important result for hydraulic engineering applications is that the minimum mesh resolution for submerged flows is completely different compared to nonsubmerged flows. The simulations are compared to physical experiments from the literature. With sufficient mesh resolution, an average relative error in capacity of 2% across the simulations is achieved for the finest mesh resolution compared to physical experiments.

Glacierised Peruvian mountain ranges are experiencing accelerated, climate-change-driven glacier ice loss. Peru's second highest mountain range, the Cordillera Huayhuash, has lost about 40 % (∼ 34 km²) of its glacier cover since the 1970s. Newly exposed landscapes are prone to a number of hazard processes including the formation and evolution of glacial lakes, changing stability conditions of mountain slopes, and rapid mass movements. In this study, we integrate the analysis of meteorological data, remotely sensed images and field observations in order to document the most recent (February 2023) large mass-movement-induced glacial lake outburst flood (GLOF) from the moraine-dammed Lake Rasac. The GLOF was triggered by a mass movement from the failure of a part of an arête ridge (i.e. narrow ridge separating parallel glacial valleys) with an estimated volume of 1.1×10⁶ m³–1.5×10⁶ m³. This occurred in a rock zone where climate information – primarily from reanalysis data – indicates cold, deep permafrost and was preceded by several small-magnitude precursory rockfall events. The reduced stability of the frozen rocks in the detachment zone is most likely related to deep warming but not to especially critical conditions of warm permafrost with higher amounts of unfrozen water. Further, we describe the surprisingly short-distance process chain (attenuated by Lake Gochacotan, located 3.5 km downstream from the detachment zone) and analyse the transport of large boulders with the use of hydrodynamic modelling, revealing that flow velocities >5 m s⁻¹ must have been reached in the case of translational motion and >10 m s⁻¹ in the case of rotational motion of the largest transported boulders (diameter >3.5 m). In addition, we analyse climate trends over the past 8 decades and meteorological conditions in the days prior to the GLOF, revealing a statistically significant temperature increase trend over the past 8 decades, as well as an atmospheric temperature rise and positive thermal anomaly in different soil layers before the event. We argue that climate change effects (warming air and permafrost temperatures) served to hasten the failure. This study helps us to understand (i) mechanisms, amplification and attenuation elements in GLOF process chains and (ii) frequency–magnitude relationships of extreme geomorphic processes that undergo alteration due to the rapidly changing high-mountain environments on a regional scale (both large-magnitude rockfalls and GLOFs). This study supports earlier work that indicated an increasing frequency of large mass-movement-induced GLOFs originating from the warming cryosphere in recent decades.

This study numerically investigates and compares the secondary currents, velocity dips, turbulence properties, and boundary shear stresses in supercritical narrow open channel flows (OCFs) ...