Interaction of Hydraulic Structures with Air, Water, and Rock: The Challenge of Researchers and Designers

Since the last ten years, financial crisis has strongly impacted the global economy, which was mainly the result of un-controlled financial speculations at the stock markets highlighted by the revelations regarding offshore companies. Fortunately, the field of construction of large infrastructures, such as hydraulic schemes, has been left relatively untouched by this crisis. In order to stimulate their economies, many governments across the world have injected significant sums into sustainable infrastructures development

Effect of deflector aerator on stepped spillway flow

Systematic physical model tests are performed on a stepped spillway equipped with a bottom aerator at the beginning of the stepped part. A deflector is used to issue a jet in order to initiate air entrainment into the flow. A horizontal slot located in the vertical face of the first step allows for air supply underneath the flow. The cavity subpressure was measured to ensure optimal aerator performance, namely atmospheric pressure conditions. The air discharge entrained below the jet is measured to derive the aerator air entrainment coefficient. The local air concentrations are spatially measured downstream of the aerator at regularly spaced profiles, allowing the investigation of air transport and detrainment as well as the average and bottom air concentrations. The present paper focuses on the resulting spatial distribution of air concentration for five deflector geometries. The chute angle, step height, approach flow Froude number and approach flow depth were kept constant, so that the differences occur mostly on the jet length and air entrainment coefficient. The flow depth and the air concentration rapidly converge towards quasi-uniform flow values downstream of the aerator

Influence of Density of Large Stems on the Blocking Probability at Spillways

Dam safety is strongly linked to the probability of occurrence of large floods. Floods can transport large wood (LW) into reservoirs and towards water release structures as spillways. Due to blocking and clogging, LW may significantly influence the discharge capacity of spillways and thus result in a dangerous rise of the water level in the reservoir. For a better assessment of the related risk, the behaviour of LW in contact with hydraulic structures has to be known. Thus the understanding of LW blockage processes at the spillway and the resulting water level rise in the reservoir is important for the safety evaluation of a dam. The aim of the present study is to describe how LW characteristics can influence blocking probabilities at a spillway inlet equipped with piers. By investigating the parameters linked to LW blockage like slenderness and density, or different hydraulic conditions and transport scenarios, it becomes possible to quantify the behaviour and consequences of LW interactions with spillways. Through systematic laboratory experiments, the influence of LW density on blocking probabilities of individual stems is analysed. Experiments were conducted for reservoir approach flow type, implying small magnitudes of reservoir flow velocity. The results were considered statistically as Bernoulli experiments and the methodology applied was a logistic regression. For the combinations explored, a relation between blocking probability and density, among other parameters, is studied

Analyse von Fliessgeschwindigkeiten und Wassertiefen auf verschiedenen Typen von Blockrampen

Im Rahmen seiner Masterarbeit hat Herr Markus Studer systematisch die Fliessverhältnisse auf verschiedenen Typen von Blockrampen untersucht, welche im Labor nachgebildet wurden. Dies erlaubte die Messung von Fliessgeschwindigkeiten sowie Abflusstiefen in einem sehr engen Raster. Die kritischen Abflussbedingungen für den Fischaufstieg konnten so mit statistischen Analysen verdeutlicht werden. Nach der Masterarbeit wurde die Studie noch mit zusätzlichen Laborversuchen ergänzt. Zudem wurden auch auf zwei Blockrampen im Felde Messungen durchgeführt. Die Arbeit von Herrn Studer kann wertvolle Hinweise geben wie eine Blockrampe strukturiert werden sollte, damit günstige hydraulische Bedingungen für den Fischaufstieg vorherrschen

Hydraulic scaled model tests for the optimization of approach channel excavation and approach flow conditions of haraz morning glory spillway

Haraz dam under construction is located along Tehran-Amol road, 20 km upstream of the Amol city. A tunnel has been designed to detour the traffic temporarily around the dam site to avoid any closure of the main road. This tunnel will be integrated in the morning glory spillway of the dam. According to the road design constraints and the tunnel layout, the morning glory entrance is located next to the dam abutment. This is the main challenge in Haraz spillway in comparison with conventional morning glory spillway approach channel. A spillway hydraulic model was set up in Tehran Water Research Institute and the corresponding tests were performed on it subsequently. According to the test results and as expected, some disturbances in the stream lines were observed of the approach flow nearby the abutment which had some negative impacts on the spillway capacity and its performance. Several alternatives were studied to optimize the hydraulic conditions using the hydraulic model. Finally, taking advantage of piers in a specific position on the ogee crest was found to be the most promising solution for reducing flow disturbances. This method could be an innovative solution for morning glory spillways, which have to be located close to the abutments

Jets opposing turbidity currents and open channel flows

Hydraulic jumps at the tail end of spillways are usually induced by baffle blocks or other obstacles. Such jumps can also be induced by jets that oppose the main flow. Another application is to back up turbidity currents in reservoirs by means of opposing jets. This measure can be adopted when transfer tunnels feed water into the reservoir at a higher elevation near the dam. Stopping the turbidity current increases the local sedimentation rate. To reconcile the shallow water equations for turbidity currents with those for open channel flows, massbased scales for the depth and velocity of both types of flows are outlined. The continuity and momentum equation for flows opposed by jets are then stated in terms of these scales and expressed by a single curve for both gravity currents and free surface flows. The corresponding results for free surface flows agree well with those of experiments carried out for this study. An application to turbidity currents is provided as well