The presence of small weirs, far more numerous than dams, has increased habitat fragmentation on rivers worldwide. This study aims to evaluate the upstream passage performance of a potamodromous cyprinid, the Iberian barbel (Luciobarbus bocagei), over an experimental broad-crested weir by varying key-hydraulic parameters. Fish passage success was studied for different combinations of waterfall height (Δh), plunge pool depth (D) and flow discharge (Q). The flow pattern downstream of the weir was characterized with a 3D Acoustic Doppler Velocimeter, to assess the effects of hydrodynamics on fish behaviour. D, Δh, and their interaction D × Δh as well as Q were correlated with the number of successful upstream fish passes. However, counter-intuitively, higher fish passage success did not occur at combinations of lower Δh and Q, and higher D. Therefore, upstream fish passage appears to be a complex phenomenon, which is strongly dependent on the hydraulic environment that is produced by the interaction of these parameters. The outcomes of this work will help engineers and biologists to establish design criteria for requalification of small barriers in order to improve fish passage and habitat connectivity.

The prediction of the pressure inside the air pocket in water pipelines has been the topic for a lot of research works. Several aspects in this field have been discussed, such as the filling and the emptying procedures. The emptying process can affect the safety and the efficiency of water systems. Current research presents an analysis of the emptying process using experimental and computational results. The phenomenon is simulated using the two-dimensional computational fluid dynamics (2D CFD) and the one-dimensional mathematical (1D) models. A backflow air analysis is also provided based on CFD simulations. The developed models show good ability in the prediction of the sub-atmospheric pressure and the flow velocity in the system. In most of the cases, the 1D and 2D CFD models show similar performance in the prediction of the pressure and the velocity results. The backflow air development can be accurately explained using the CFD model.

The quantification of the breach hydrograph of an overtopped earth dam remains a challenge, even in controlled laboratory conditions. In this work, the breach hydrograph is calculated as the product of the velocity normal to a breach cross section and the estimated area of that cross section. Although theoretically simple, because it is based on the very definition of discharge, this direct approach is an absolute novelty in dam-breach studies. To illustrate the application of the method, a laboratory model of an earth dam, built with cohesive sediments, was closely monitored. Competent velocities were estimated from surface velocity maps measured with large-scale particle image velocimetry (LSPIV). The breach area was estimated by analyzing images of the traces of a laser sheet on the free surface and the breach bottom. The direct breach hydrograph was compared with an estimate based on the mass balance in the reservoir and with the discharge obtained through a rating curve of a downstream spillway. The novel method was shown to reproduce the main expected features of the breach hydrograph. The potential to provide estimates free from experimental artifacts caused by improper description of inertial effects is underlined. The advantages and the difficulties inherent to the method are discussed.

Literature related to pool‐type fishways has seen a recent upsurge of interest in the placement of instream structures for improving fish passage. However, there is still no information on how different flow regimes created by boulder placement have an influence on upstream fish movements. The main goal of this study was to assess the performance of two different flow regimes, characterized by the relative depth of flow (d/h), where d is the water depth and h is the height of artificial bottom substrata, in assisting fish passage in an experimental full‐scale pool‐type fishway. Two series of experiments consisting of 20 replicates each and representing distinct flow regimes created by boulder placement in the flume bottom – d/h > 4 (regime 1) and 1.3 < d/h < 4 (regime 2) – were carried out to analyse the proportion and timing of successful upstream movements of a potamodromous cyprinid, the Iberian barbel (Luciobarbus bocagei). Although no significant differences (P > 0.05) in passage success were observed between regimes (55% and 60%, respectively), fish transit time was significantly lower (P < 0.05) in regime 2 (mean ± SD: 2.6 ± 1.6 min.) than in regime 1 (7.1 ± 5.8 min.). The results of these experiments show that lower relative depths can be more beneficial to fish passage because they reduce the transit time for successful negotiation, thus providing a useful indication on how to improve fish passage through pool‐type fishways.

An experimental assessment of an air pocket (AP), confined in a compressed air vessel (CAV), has been investigated under several different water hammer (WH) events to better define the use of protection devices or compressed air energy storage (CAES) systems. This research focuses on the size of an AP within an air vessel and tries to describe how it affects important parameters of the system, i.e., the pressure in the pipe, stored pressure, flow velocity, displaced volume of water and water level in the CAV. Results present a specific range of air pockets based on a dimensionless parameter extractable for other real systems.

The occurrence of sub-atmospheric pressure in the drainage of pipelines containing an air pocket has been known as a major cause of several serious problems. Accordingly, some system malfunction and pipe buckling events have been reported in the literature. This case has been studied experimentally and numerically in the current research considering objectives for a better understanding of: (i) the emptying process, (ii) the main parameters influencing the drainage, and (iii) the air-water interface deformation. Also, this research demonstrates the ability of a computational fluid dynamic (CFD) model in the simulation of this event. The effects of the air pocket size, the percentage and the time of valve opening on the pressure variation have been studied. Results show the pipeline drainage mostly occurs due to backflow air intrusion. The worst case scenario is associated with a fast valve opening when a tiny air pocket exists in the pipeline.