The Piano Key Weir (PKW) has emerged as an effective solution for enhancing the discharge capacity of spillways, particularly in low-head dams. This study presents an experimental investigation comparing two Type A PKW models that differ solely in the geometry of their outlet keys: linear (L-PKW) and curvilinear ogee (CL-PKW). Laboratory tests were conducted under free-flow conditions, and H/P ratios (where H is the upstream head above the crest and P is the weir height) between 0.17 and 0.63 were analyzed in detail. The results suggest that CL-PKW shows improved discharge efficiency relative to L-PKW, with observed increases ranging from 12.4% to 18.1% across the tested conditions. The curvilinear ogee outlet key, derived from the Waterways Experiment Station (WES) standard spillway profile and fabricated as a smooth, curved slab, reduces nappe interference and flow separation, contributing to a higher discharge coefficient. A novel empirical equation was developed using 90 data points, including results from the present study and previous literature, to predict the discharge coefficient of Type A PKWs with both outlet key types. Comparative analysis with existing equations indicates that the proposed equation provides predictive accuracy comparable to, and in some cases slightly better than, established formulations, with 88% and 100% of data points falling within 9% and 12% absolute error bounds, respectively. The proposed equation also exhibited lower root mean squared error (RMSE) and mean absolute percentage error (MAPE) values, indicating a predictive performance that is comparable to, and in some cases modestly better than, existing empirical equations for different outlet geometries and flow conditions. By addressing the overlooked influence of outlet key geometry, this study fills a critical research gap and introduces a versatile tool for discharge prediction. The findings offer practical guidance for hydraulic engineers in the design and optimization of PKWs for spillway improvements and dam safety upgrades.

In the present era, sedimentation and bed morphology near hydraulic structures is a great concern as it affects the flow configuration and reduces the discharge capacity. Experimental investigations were done to study the flow field in the vicinity of one cycle, two cycle, and three cycle piano key weirs (PK weirs) with noses to monitor the sediment passing capacity of the weir. The three dimensional (3D) velocities were measured close to the inlet and outlet keys using an acoustic Doppler velocimeter (ADV). The velocity fields near both the inlet and outlet keys were examined, and it was found that there were considerable increases in the vertical (v-component) and lateral (w-component) velocities. Added to this, it was seen that the mean vertical velocity was more in front of the outlet key as compared to the front of the inlet key while the mean lateral and longitudinal velocities were low. The maximum velocity was observed in front of the inlet key which resulted in an increase of sediment movement over the PK weir. Furthermore, 2.6%-5.2% of the total sediment passing over the upstream portion of the weirs are flushed over the inlet key by self-cleaning. The flow field over the keys could not be accurately estimated using an ADV, possibly due to the flow complexity so computational fluid dynamics (CFD) simulations were done to understand the complex flow field for all the three PK weirs using a CFD solver which needs less computational cost and space. The widely used standard k-epsilon epsilon turbulence model (an eddy-viscosity model) was applied in the current numerical investigations. The numerical investigation shows that the magnitude of the velocity components was increased because of the vertical contraction in front of the sloped keys owing to very high flow immediately downstream of PK weirs. (c) 2024 International Research and Training Centre on Erosion and Sedimentation. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Nowadays, piano key (PK) weir with an expanded crest length are often used to deal with surplus discharge in dams due to unexpected climate change effects, increasing safety. The present study deals with the numerical modelling of a group of PK weirs with auxiliary geometrical parameters to predict the flow over a PK weir using different FLOW-3D turbulence models. The numerical outcomes were compared with the experimental results to check the accuracy of the underlying FLOW-3D models. It was found that the k-𝜀 turbulence model of FLOW-3D estimated the flow over a piano key weir more closely to the experimental results than the RNG (renormalized group) and LES (large eddy simulation) models. Statistical parameters were used to evaluate the simulated results. It was observed that the coefficient of correlation (CC) was close to one and the root mean square error (RMSE) close to zero when numerical outcomes were compared with experimental datasets. The results show that the FLOW-3D software is quite effective in estimating the flow. Therefore, the present study will help to understand the best combination of mesh, models, adaption and convergence processes in simulation and provide an insight into the numerical analysis of flow configuration over PKW by considering one of the best numerical models.

The existing equations for the discharge coefficient of Piano key weirs (PKWs) use a limited range of experimental data, which means that they are inappropriate for wide parametric ranges that might lead to significant errors. This study aimed to propose a reformed empirical equation using a wide range of data points gathered from previous experimental studies. Further, the appropriateness to use the existing equations for the collected data points, and the related errors, were investigated in detail using graphical and statistical analyses. The proposed equation predicted the discharge coefficients with < 5% absolute errors for 83.5% data points and with < 10% absolute errors for 100% data points, and the mean absolute error was 2.9%. Such variations may be attributed to the differences in experimental conditions that exist among the previous studies. The correlation indices were higher for the proposed equation as compared to the same for the existing equations, whereas the error indices were lowest for the proposed one. For some very specific parametric ranges, the existing equations still hold better accuracy. Overall, the proposed equation can precisely estimate the discharge coefficient of the basic geometry of Type-A PKWs for a wide parametric range and will be handy in the hydraulic design of such PKWs.

Vegetation forms an integral part of ecological system in river engineering. Aquatic vegetation found in streams and rivers can be broadly classified as floating, submerged and emergent vegetation. The current study deals with analyzing the turbulence characteristics in a vegetated channel. Experiments were carried out using rigid and flexible vegetative models installed in the open channel flume. Velocity data at different measurement points were collected using Acoustic Doppler Velocimeter (ADV). A constant discharge was maintained throughout the experiment. It was observed that the presence of vegetation can significantly influence the turbulence charac-teristics in a channel. The Reynolds shear stress as well as the turbulence intensity was found to decrease with the vegetation. However, at the downstream sections of the vegetative models, there were significant flow fluctu-ations in the case of both rigid and flexible vegetations. Moreover, analysis of third-order moments revealed that vegetation attenuates the downward flow in a channel, thereby making the channel bed more stable. On the other hand, it was found that flexible vegetation can efficiently control the turbulence fluctuations as compared to rigid vegetation, hence proving to be better alternative when it comes to river protection works. Further comparison was also presented with an existing literature to get a more comprehensive idea in this field. Therefore present study provides an insight into the fact that with the help of flexible and rigid vegetation one can restore the ecological balance in the river. The riparian vegetation would be very useful for the river engineers and managers to improve the ecosystem health.

Riparian vegetation could be an appropriate solution for the flood control and sustainable river management technique as it is useful for the energy dissipation of the stream flows. The present experimental investigation is conducted to understand the flow configuration and energy dissipation of stream flows considering the flexible and rigid vegetation. The laboratory-based physical models are tested in a rectangular flume to observe the flow field in the upstream and downstream of both the vegetations. In this study, rigid vegetation is considered of wooden dowels of equal height and almost uniform diameter whereas for flexible vegetation paddy plants were used. Acoustic Doppler Velocimeter is utilized to observe the velocity profiles at different sections and then it is compared with and without the vegetation. It is noticed that around 24% reduction in stream velocity occurs due to introduction of rigid vegetation whereas 90% reduction happens due to flexible vegetation in the channel. Additionally, energy dissipation at all the sections of both vegetation types was found to give a more comprehensive understanding of the flow field. Overall, the present study provides an insight into the fact that with the help of flexible and rigid vegetation one can restore the ecological balance in the river. The vegetation with high density, height and flexibility will be useful for the dissipation of energy in effective manner. This study also suggests that flexible vegetation will be an effective tool in river management by decreasing scouring in the channel, thereby reducing erosion and sediment discontinuity.

A Piano key weir (PKW) is a modern type of spillway that is used to improve the discharge capacity of dams. The ongoing work on this complex structure is very challenging nowadays for engineers and researchers all over the world. Regardless of this, several prototypes have been successfully installed over the years to enhance the discharge capacity of existing dams. For better understanding the analysis of flow hydraulics and its effects near and over the weir has been studied in this chapter. The present study deals with the effect of different shapes and sizes of PKW on the discharge capacity, variation in scours pattern downstream of the PKW (with or without apron), energy dissipation across the PKW from different techniques, and analyzing it from the channel bed slopes. Numerous numbers of experiments and modeling techniques have been encapsulated in this chapter. This chapter aims to present fundamental outcomes from various experimental studies on different performances carried out on PKW over the years. Here, this chapter discusses some of the analyses from various works that have been done in past either numerically or experimentally so that the reader gets ample knowledge while conducting research in this field. Furthermore, the chapter highlights the significant results and identifies some research gaps that have not been conducted earlier.

The presence of an upstream ramp in a triangular (hump) weir (TW-UR) increases its discharging capacity and sediment passage possibilities than traditional weirs. Presented in this paper is an experimental investigation on the tracking of incipient movement of individual sediment particle sizing from 1.4 to 3.07 mm over the channel bed upstream of a TW-UR and its ramp. The sediment movements were recorded by a high-speed camera and analysed using image processing techniques. The shear stress on smooth upstream bed was calculated using Acoustic Doppler Velocimeter. The critical condition for sediment movement over upstream bed and its regime were compared with previous investigations. Furthermore, Computational Fluid Dynamics simulation was performed to compute the shear stress on the upstream ramp. It was found that sediment loses its velocity while approaching the ramp and stops momentarily at the toe of the ramp. The maximum particle velocity at the end of the ramp varies from 0.47 to 0.78 m s−1. Enhanced hydrodynamic force along the ramp increases the particle kinematics. A rapid increase in shear stress was observed in the downstream part of the ramp. The ratio of maximum particle velocity to flow velocity near the ramp end is around 0.75. It was found that about 20–60% of additional shear stress is required to move particles over the ramp. The present study is useful for maintaining the sediment continuity in channels using triangular (hump) weirs which are basically used as embankment weirs.

Piano Key Weirs (PKWs) are often preferred over other spillways for the dam rehabilitation due to high discharging capacity. The present study investigates scour downstream of three cycles of PKWs with and without solid apron under both free and submerged flow conditions. The scour formations downstream of the inlet and outlet keys were investigated by varying discharges and tail water depths. Three different types of aprons were used under varied discharges and tail water depths. Falling and impinging jets emanating from inlet and outlet keys were noted as being responsible for the formation of ridge and dip, respectively. The maximum depth of scour was 40%-80% of the total weir height under different discharges. For high submergence, negligible scour development was reported. The average reduction in the scour depth with a solid apron lies in the 60%-80% range. Empirical equations were developed using a least square technique for the computation of maximum scour depth for both the conditions, that is, with and without a solid apron. Statistical and graphical analysis indicates better conformity of the proposed equation with the previous investigation. Sensitivity analysis indicates that the ratio of tailwater depth to the median size of a sediment particle (y(t)/d(50)) and the ratio of the crest length to the width of the weir (L/W) are the most sensible parameters affecting maximum scour with and without a solid apron, respectively. (C) 2021 American Society of Civil Engineers.

Vegetation such as submerged, emergent, and floating plays an essential role in altering the flow characteristics through a channel. Moreover, vegetation serves as a means for the ecological restoration of a river and the prevention of erosion. Hence, understanding the changes that take place in the flow as it flows through vegetation forms the crux of the river restoration and erosion prevention works to name a few. For understanding the hydrodynamics of vegetation, various experiments have been carried out throughout the years along with the arrangements of numerous models. Properties such as Flow velocity, Reynolds Shear Stress (RSS), and Turbulent Intensities, etc. are extensively studied to understand this complex flow-vegetation interaction in a much better way. This chapter aims to introduce the readers to the changes occurring in such properties due to vegetation; found by various experiments over the years, in a detailed manner. Studies and results based on the different experimental set-ups in terms of vegetation type, arrangement, etc. have been put forward in the study such that the readers can gain an insight into the comparative study in this field of research. The chapter concludes by highlighting the important results as well as the research gaps in this field of study.

This investigation deals with the mechanics of movement of singular quartz gravel and coarse sand riverbed particles upstream and over the inlet key of three Type A piano key weir (PKW) models, which were recorded with a high-speed camera. Acoustic Doppler velocimeter was used to obtain the upstream bed shear stress. The sediment threshold and regime over the upstream bed were compared with the previous investigations and found to be within the ranges. Generally, a sediment particle decelerates as it approaches the inlet key, but accelerates over it due to flow contraction and an increase in shear stress. Rolling and saltation regimes were observed over the key. The maximum particle velocity at the key end was highest in the 1-cycle model, then the 2-cycle model, then the 3-cycle model. Computational fluid dynamics (CFD) simulation shows a rapid increase in shear stress at the key end. For the used models, PKW required 17%-43% of additional shear stress on the upstream bed to pass sediment over the key. This study is useful for the in-channel application of PKW and sediment flushing over it. (C) 2021 American Society of Civil Engineers.

The application of a piano key (PK) weir in a channel may lead to changes in the flow characteristics, upstream siltation conditions, and bed elevation. In this study, laboratory-based Type-A PK weir models with noses below the upstream apexes were studied under different flow and siltation conditions. A total of 342 datasets were collected from the three models. Upstream siltation had no impact on the discharge efficiency of submerged PK weirs, but under the free-flow condition, there was a maximum reduction of 4% in the coefficient of discharge. Planners and designers must consider such variations in channels with a high sediment load. However, at high H/P (where H is the head over the weir crest and P is the weir height), the siltation effect starts to decrease, possibly due to the alternation in the flow condition caused by tailwater submergence. The modular submergence was found to be approximately 0.5, which is close to the values available in the literature. The proposed equations for free-flowing PK weirs performed very well with a maximum error of approximately 7% and a mean absolute percentage error (MAPE) of approximately 2.5%. Furthermore, approximately 60% of the data lie within the ± 3% error bands, and almost all data lie within the ± 6% error bands. The equations proposed for submerged PK weirs also efficiently estimated the coefficient of discharge with a maximum error ranging from 9.0 to 11.32% and an MAPE varying from 2.94 to 4.27%.

Many dams around the world are ageing and require upgradation in terms of spillway capacity and other safety aspects. In recent times, challenges faced due to global warming, climate change and cloudburst events have grown not just in numbers but also in extremity. Consequently, several dams and diversion structures are being modified to cope up with the floods resulting from such events. Piano key weir (PKW) has effectively been used in many dam upgradation projects, especially in France and Vietnam, to enhance the discharge capacity of the existing ogee-crested weirs or labyrinth weirs. It has also been used in a diversion scheme in India (Sawra Kuddu). The flow field around a PKW is spatially varied, complex and three-dimensional in nature. The previous researches on PKWs were predominantly focused on the effect of different parameters on its discharging capacity and limited studies are available on the flow field, sediment movement and scouring at PKWs. Considering these gaps, this study was initiated to understand the flow pattern near PKW and its effect on the sediment transport over PKW. Presented here is the experimental work carried out at IIT Roorkee, India on a Type-A PKW flume model with two discharge values, the CFD simulations of those two flow conditions and a comparison between the results. The time-averaged velocity values were measured at different locations in the front of inlet and outlet keys (upto a distance of 0.1 m from the bed level) using a 3D Acoustic Doppler Velocimeter. The simulations were performed in Ansys (academic 19.1) CFX solver using finite volume method, standard k-ε turbulent model, (where k denotes the turbulent kinetic energy and ε is the rate of dissipation of k) and multiphase (volume of fluid) modelling. The experimental results showed an increase in the depth-averaged longitudinal flow velocity towards the inlet, but a decrease in that towards the outlet. A significant rise in the upward velocity (in the outer flow region) towards both the keys was observed experimentally and numerically. Both the approaches also indicated a significant increase in the lateral velocity near the inlet, especially in the inner flow region. CFD simulations clearly showed decelerating and accelerating flow zones in front of the outlet and inlet keys, respectively, and also revealed an accelerating flow over the inlet. However, the velocity profile inside the inlet key could not be measured experimentally, possibly due to flow unsteadiness, high turbulence and flow separation, and it demands further research. The CFD results generally underestimated the velocity values for the measured 0.1 m depth of flow and the mean absolute error values for the resultant velocity were 18.32% and 15.52% for the two discharges, respectively. The rise in the approaching flow velocity components towards the inlet and the sloping key enhance the opportunity of sediment passage over a PKW in comparison to other weirs. Extending this work, the study on the flow field near two-cycles and three-cycles PKW models is undergoing.

In this paper, an attempt has been made to carry out the study of scour depth at one of the piers of the Gandhi Setu in Ganga River near Gaye Ghat, Patna. Different parameters of the different empirical equations have been calculated by collecting soil samples from the site and analyzed in the laboratory. Based on these parameters, the scour depth is calculated by using different empirical equations given by different researchers such as Shen et al., the Modified Laursen, Jain and Fischer and Lacey's. The actual scour was also measured near one of the piers of Gandhi Setu in Ganga River at Patna, in-situ measurement using the rope attached with heavy weight. It was found that the scour depth measured manually matches satisfactorily with the scour depth computed using Lacey's empirical formula.

To understand the flow field and discharge characteristics of a triangular weir with an upstream ramp (TW-UR), experimental study as well as computational fluid dynamics (CFD) simulation were performed. The Ansys CFX module and standard k-ε turbulent model were used in the simulation. It was observed that the TW-UR had about 9.8–14.3% higher discharging capacity than a sharp-crested weir of the same height and it was found that about 10–15% higher discharging capacity was estimated in the CFD simulation as compared to the observed data under the same head. The highly active flow field in the upstream side and enhanced velocity along the flow direction due to flow contraction in the vertical plane are helpful in enhancing the hydrodynamic force exerted by the moving fluid and creating the chances of sediment passage as well as increasing the discharging capacity. Existing two equations of the coefficient of discharge for TW-UR were checked for their accuracy using the present and previous experimental data, and it was observed that the equation proposed by Azimi et al. (J Irrig Drain Eng 139(1):75–83, 2013) predicted the coefficient of discharge within ±5, ±10 and ±15% error ranges for 43.0, 72.5 and 92.5% datasets, whereas within those error ranges, equation proposed by Di Stefano et al. (J Irrig Drain Eng 142(10):04016036-1–9, 2016) estimated the coefficient of discharge for 61.7, 92.3 and 100% datasets, respectively. Statistical analysis showed that in most of the cases, the equation of Di Stefano et al. (J Irrig Drain Eng 142(10):04016036-1–9, 2016) showed better precision than Azimi et al. (J Irrig Drain Eng 139(1):75–83, 2013) equation, and overall, the equation proposed by Di Stefano et al. (J Irrig Drain Eng 142(10):04016036-1–9, 2016) is more accurate than the equation proposed by Azimi et al. (J Irrig Drain Eng 139(1):75–83, 2013).

Piano key weirs (PK weirs) are generally installed on low head dams to enhance the discharging capacity. Such weirs are preferred over the other spillways if the length available for the construction of the spillway is limited and high discharge is to be passed at low head to avoid flood inundation in upstream. This newfangled weir having zig-zag shape changes the flow configurations which lead to scour downstream of the weir. A study on scour formation downstream of a PK weir is presented in this paper. Experimental investigations were conducted on three cycles PK weir to investigate scour pattern downstream of inlet and outlet keys with and without solid apron. Variation in observed maximum scour depth (ds) with tail water depth (yt) was studied to examine the effect of tail water depth on the scour for different discharges. It was observed that the falling jet and impinging jet originating from the inlet keys and outlet keys were liable for the development of dip and ridge downstream of the weir. For higher discharge and lower tail water, it was observed that scour depth and length of scour are high. Scour formation was negligible in the case of high submergence downstream of the weir. However, significant reduction in the scour was observed due to introduction of solid apron downstream of weir. Finally, the present experimental PK weir scour data were checked with the predictions provided in the literature. Two equations show correct trend for the observed scour values.

Applications of hydraulic structures in low dams and diversion structures in countries like India, where sediment is a serious concern, demands a good expanse of research on the flow field and movement of sediment. The present study was focused on the non-uniformity in the velocity distribution along the flow direction and the movement of sediment over a ramp. The velocity distribution of the flow near and over the ramp was studied with the help of Acoustic Doppler Velocimeter. Experiments were conducted to study the mechanics and kinematics of movement of sediment particles. The movement of sediment particles over the smooth ramp was studied with the help of high-speed camera system. The particle velocity, acceleration, applied force and the angle of velocity vector were processed and analyzed from the captured images using digital image analysis techniques. The path of the movement of sediment particle was tracked. The vector results of the flow pattern indicated a very high amount of increase of the uplift velocity (y – component of the instantaneous flow velocity) component over a ramp. The sediment had very little movement for about 3.8 seconds at the beginning of the ramp and accelerated as it moved along the ramp in the downstream side. The path of the sediment movement over the ramp was found to be inclined by 25.6 to 35.7 degree to the horizontal axis which was almost parallel to the ramp (29.055 degree).

In present scenario, Piano key weir has played a vital role in increasing the discharge capacity of the available dams. This modified weir is the replacement of creaky and conventional labyrinth weir and it is best suited for the low head dams. This new labyrinth type weir is utmost solution for the rehabilitation of the spillways all across the globe. There are various equations available for the estimation of coefficient of discharge of Piano key weir. The present study encapsulates about the observable fact of coefficient of discharge for the Piano key weir and assigns different procedure for its evaluation. The validation of the four existing equations given by the investigators for the coefficient of discharge is monitored in the study. The graphical representation and statistical perusal of the equations given by the investigators show that the relationship proposed by Crookston et al.; Cicero and Delisle predict coefficient of discharge better than other equations for the data sets used in this present study. For these two equations 97% results lie within ±20% error lines. The present experimental study is also compared with the relationships given by the previous investigators. The equation suggested by Crookston et al. estimates coefficient of discharge effectively for all ranges of H/P, whereas the equation proposed by Cicero and Delisle is slightly more efficient for H/P between 0.2 and 0.8.