Hydraulic model experiment of energy dissipation on the horizontal and USBR II stilling basin

Flow conditions on overflow systems can result in construction failure, mainly due to the high flow energy. Stilling basin at downstream of the spillway is useful for reducing flow energy. It can reduce the destructive force of water flow. Controlling the hydraulic jump is an important part that includes the jump’s energy, length, and height. The physical hydraulic model was carried out with several series, by making a series of bottom lowering of horizontal and USBR II stilling basin. The experimental study is expected to represent flow behavior in the overflow system regarding flow conditions and energy dissipation. Based on the analytical calculation of flow velocity, the amount of flow energy that occurs at each control point is calculated. The control points are the starting point of the spillway, the chute way toe, and flow depth after the hydraulic jump. The energy loss can be calculated for each control point, while the efficiency of energy dissipation on stilling basin is calculated at the downstream flow depth after the hydraulic jump. Velocity calculated by dividing discharge per unit width by water depth which is based on the flow depth measurement data in the hydraulic model.

Investigation Of Hydraulic Flow Characteristics On Drop Structures

Drop structures are required if the slope of the ground level is steeper than the maximum allowable gradient channel. Drop structures become bigger as height increases. Its hydraulic capability may be reduced due to variations of jets falling on the stilling basin floor due to discharge changing. Drop structures should not be used if the change in energy level exceeds 1.50 m. The free-falling overflow on drop structures will hit the stilling basin and move downstream. As a result of overflows and turbulence in the pool below the nappe, some energy is dissipated at the front. The rest of the energy will be reduced downstream. The objectives of this study are to investigate the hydraulics flow behavior in straight and sloping drop structures and to investigate hydraulics flow behavior in a single and serial vertical drop (stepped drop). The hydraulic model results of single and stepped drop structures are compared to obtain flow behavior and energy dissipation information. The comparisons are specific to the flow parameters, including flow depth at the drop structures toe, flow depth after the jump, and hydraulic jump length.

Pressure Fluctuations Characteristics of the Stilling Basin with a Negative Step

Fluctuating pressure is the main cause of the floor fatigue of the stilling basin with a negative step. Despite investigations of stilling basin with a negative step conducted by many researchers, there is not enough information about the influence of the geometric parameters on fluctuating pressure on the floor. In the present study, fluctuating pressure on the floor of the stilling basin with a negative step was systematically investigated by a total of 85 model tests. The results show that the fluctuating pressure coefficient Cp’ has a process of rapid increase and decrease, and then decreases slowly until it becomes stable, and the maximum fluctuating pressure coefficient Cp’max lies in the reattachment zone rather than in the jet impingement area for Type II-jump. The dominant frequency of the fluctuating pressure on the floor shows a decreasing trend along stilling basin. With the increase of the step height, the Cp’max presents decreasing trend but X*0 where the Cp’max occurs increasing trend. While there has on obvious regularity between incident angle and Cp’. Finally, according to the fitting of test data, an empirical formula to calculate Cp’max is developed. These research results provide reference for the design of stilling basin with a negative step in engineering applications.

Investigation of scours on a physical model of the Hričov weir using photogrammetry

Scours creation in riverbed at the Hričov weir is a permanent problem since its construction. It is caused by the shortened stilling basin of the weir. In almost all cases of flow control at the weir the energy is not dissipated sufficiently. A 3D physical model was built in the hydraulic laboratory to investigate the measures for reduction of the scour creation. To simulate uneven loads on the downstream riverbed, a flood discharge controlled by the weir in symmetric and asymmetric operations was used for simulations. The scours were evaluated using short-range photogrammetry for contactless measurements. Based on this method digital models of the riverbed for each simulation were created and the scours were assessed to determine the effect of the investigated measures on scour reduction.

Effect of Energy Dissipation on Scour Hole Development Downstream of the Chute

An energy dissipation on hydraulic structures is a scientifically highly examined field of study. Gained knowledge can be used to ensure the safety of the hydraulic structures and the channels which is crucial during floods. Above that, those structures are also part of the critical infrastructure therefore their function is necessary. It is assumed that in the Czech Republic the precipitation distribution is changing due to climate change thus episodes of extreme floods may be observed more often. The paper brings brand new knowledge on the kinetic energy dissipation on the chute and in the stilling basin and its impact on the riverbed scour hole development. The presented research was conducted in the Water Management Experimental Centre of Czech Technical University in Prague, Faculty of Civil Engineering. The research aimed to examine the energy dissipation mechanism on different geometric modifications of the construction of spillway chute and stilling basin and its impact on the process of scour hole development. These various types of dams’ flood safety equipment were examined in the hydraulic laboratory: an elementary form of the spillway without any stilling basin; the elementary form of the spillway and the stilling basin (crest and spillway channel had the same width); the chute width was reduced, and the stilling basin had the full width; steps were added on the narrowed chute and the and stilling basin had the full width; only the spillway crest was reduced to a half-width; only the stilling basin width was smoothly reduced; the chute’s width was smoothly reduced along the chute and the stilling basin had full width; the chute’s width was smoothly reduced along the chute and the stilling basin had the width reduced to a half. The flow, water levels, scour hole and deposit dimensions were measured. Then the amount of energy dissipated was computed. The correlation and connection between energy dissipation and scour hole development was investigated. These outcomes can be used as a recommendation of an appropriate construction design to provide better flood safety of the hydraulic structure.

Model Investigations of Scouring at the Hričov Weir Using Short-Range Photogrammetry

Stilling basins are commonly used to efficiently dissipate energy of flow at weirs. Different types of stilling basins are used at weirs due to different conditions – hydraulic, operational, constructional. At the Hričov water structure a short stilling basin has been built. Its operation over the years showed that it does not dissipate the energy of the flowing water sufficiently, which causes intense scouring in the riverbed downstream. To partially deal with this problem and to protect the riverbed from scours, a rockfill embankment supported with a steel construction was constructed adjacent to the stilling basin’s toe. Despite this riverbed fortification, scours are being created in the riverbed and even in the fortification itself for different cases of operation conditions of the weir. A hydraulic research on a scaled model of the weir was used to investigate the problem and to propose a permanent solution significantly improving the scouring downstream the weir. The proposed fortification of the riverbed downstream the weir was tested at different operational conditions, which simulated extreme situations at the weir. To assess the effects of the investigated fortification, the simulations were performed for the weir without and with the fortification. After each simulation, the deformations in the riverbed (scours) were measured and evaluated. For measuring the riverbed deformations on the model, the method of short-range photogrammetry was used as a very effective and contactless method. This method allowed to examine the investigated area with a very high accuracy and speed. Digital models of the riverbed deformations created after each simulation on the hydraulic model were used to determine the locations and sizes of the deepest scours. Final assessment of the results showed the improvement in the reduction of scouring by the proposed fortification by almost 50% in the size of the scours. The investigations and the results are described in this paper.

Predicting the Flow Velocity at the Toe of a Labyrinth Stepped Spillway

The velocity at the toe of a spillway is a major variable when designing a stilling basin. Reducing this velocity leads to reduce the size of the basin as well as the required appurtenances which needs for dissipating the surplus kinetic energy of the flow. If the spillway chute is able to dissipate more kinetic energy, then the resulting flow velocity at the toe of spillway will be reduced. Typically, stepped spillway is able to dissipate more kinetic energy than that of a smooth surface. In the present study, the typical uniform shape of the steps has been modified to a labyrinth shape. It is postulated that a labyrinth shape can increase the dissipation of kinetic energy through increasing the overlap between the forests of nappe will circulating the flow that in turns leading to further turbulence. This action can reduce the jet velocities near the surfaces, thus minimizing cavitation. At the same time the increasing of circulation regions will maximize the opportunity for air entrainment which also helps to dissipate more kinetic energy. The undertaken physical models were consisted of three labyrinth stepped spillways with magnification ratios (width of labyrinth to width of conventional step) WL/W are 1.1, 1.2, and 1.3 as well as testing a conventional stepped spillway (WL/W=1). It is concluded that the spillway chute coefficient is directly proportional to the labyrinth ratio and its value decreases as this ratio increases.