The assessment of scour depth downstream of weirs holds paramount importance in ensuring the structural stability of these hydraulic structures. This study presents groundbreaking experimental investigations highlighting the innovative use of baffles to enhance energy dissipation and mitigate scour in the downstream beds of rectangular piano key weirs (RPKWs) and trapezoidal piano key weirs (TPKWs). By leveraging three state-of-the-art supervised machine learning algorithms—multi-layer perceptron (MLP), extreme gradient boosting (XGBoost), and support vector regression (SVR)—to estimate scour hole parameters, this research showcases significant advancements in predictive modeling for scour analysis. Experimental results reveal that the incorporation of baffles leads to a remarkable 18–22% increase in energy dissipation and an 11–14% reduction in scour depth for both RPKWs and TPKWs. Specifically, introducing baffles in RPKWs resulted in a noteworthy 26.7% reduction in scour hole area and a 30.3% decrease in scour volume compared to RPKWs without baffles. Moreover, novel empirical equations were developed to estimate scour parameters, achieving impressive performance metrics with an average R² = 0.951, RMSE = 0.145, and MRPE = 4.429%. The MLP models demonstrate superior performance in predicting maximum scour depth across all scenarios with an average R² = 0.988, RMSE = 0.035, and MRPE = 1.036%. However, the predictive capabilities varied when estimating weir toe scour depth under diverse circumstances, with the XGBoost model proving more accurate in scenarios involving baffled TPKWs with R² = 0.965, RMSE = 0.048, and MRPE = 2.798% than the MLP and SVR models. This research underscores the significant role of baffles in minimizing scouring effects in TPKWs compared to RPKWs, showcasing the potential for improved design and efficiency in water-management systems.

In this paper, the scour downstream of a trapezoidal Piano key weir (PKW) is investigated under free and submerged flow conditions. For this purpose, an experimental model was used in a laboratory channel with a length of 10 m, width of 0.75 m, and height of 0.8 m at various discharges and tailwater depths. The results showed an increase and decrease in the maximum scour depth with an increase in the discharge and submergence ratio, respectively. In addition, increasing the particle Froude number enhanced the geometric features of the scour hole downstream of the PKW. The rate of bed changes slowed down over time. The average values of maximum scour depth, the distance of the maximum scour depth from the weir toe, maximum scour hole length and weir toe scour depth increased in the free flow compared to the submerged flow. The scour hole volume and scour hole area in the submerged flow were less compared to the free flow. The average maximum level of the sedimentary ridge in the free flow is less than the submerged flow. New equations for calculating the geometric characteristics of the scour hole downstream of the trapezoidal PKW are presented with acceptable accuracy.

This study investigates the effectiveness of flow splitters in reducing scour downstream of trapezoidal Piano Key Weirs through a comprehensive experimental study. Three distinct geometries of flow splitters—square, rectangular, and circular—are examined under various hydraulic conditions to assess their impact on local scouring. The experiments were conducted in a dedicated channel measuring 10 m in length, 0.75 m in width, and 0.80 m in height. The results indicate that flow splitters facilitate flow separation by linking trapped air beneath the flow to the free surface, thereby mitigating nappe oscillation. Additionally, the geometric variations of flow splitters did not significantly influence the upstream water head, with rectangular-shaped flow splitters proving more effective than square and circular splitters. On average, the maximum scour depth for the weir with rectangular, square, and circular splitters is reduced by approximately 13, 11, and 10%, respectively, compared to the weir without splitters. Furthermore, the volume of scour holes in tests with rectangular, square, and circular splitters showed reductions of 18.53, 17.77, and 14.92%, respectively, compared to tests without splitters. As discharge decreases, the effectiveness of these flow splitters in reducing scour depth becomes more pronounced. Due to the existence of splitters, the location of maximum scour depth approaches the weir. New equations were developed for predicting scour hole parameters with and without flow splitters, incorporating various splitter geometries. These equations were formulated using non-linear regression, achieving high accuracy with a correction factor, yielding R² values between 0.78 and 0.94, and RMSE values ranging from 0.09 to 0.54. Overall, the findings underscore the significance of flow splitter geometry in mitigating scour effects, providing valuable insights for future engineering applications.