Optimization of Hydraulic Design of Spillways and Its Appurtenant Structures—Role of Physical Model Studies

Optimization in the design of spillway and energy dissipator is one of the crucial parts of the safety of the dams. Most of the hydropower projects are planned/under construction/commissioned in the north and north-east region due to high hydropower potential. Due to the steep slopes and fragile geology, the soil erosion rate is high during snowmelt and monsoon causing severe sedimentation problems. Considering topography, geology, and other site constraints, the design of a spillway is a challenging task for the design engineers. The design of the spillway for each project is unique and site specific. Physical model studies are an indispensable tool for analyzing the flow and optimizing the design of various components of spillway before execution at the site. The present paper emphasizes the role of the physical model to optimize the design of spillway and its appurtenant structures for the Arun 3 dam spillway, Nepal, which is under construction at the site. The sluice spillway is designed for passing the flood and flushing of sediments from the reservoir. Considering the dual purpose of the spillway, extensive studies were carried out for various ranges of discharges up to design discharge of 15,710 m3/s for gated and ungated operation of spillway at CWPRS, Pune. Parametric studies were carried out especially for optimizing the design of ski-jump bucket considering the various upstream reservoir water levels and downstream tail water levels to achieve the satisfactory performance of energy dissipation. The findings obtained from the studies for the said project are discussed in detail in the paper. The physical model studies became useful to design the structure economically and hydraulically efficient.