<b>IMPROVING THE HYDRAULIC CALCULATION METHOD FOR WATER DISCHARGE STRUCTURES</b>

Dams whose failure may pose a threat to human life or result in substantial economic losses must be designed to safely withstand the Probable Maximum Flood (PMF). In Uzbekistan, the impacts of climate change, irregular precipitation patterns, and accelerated glacier melting in mountainous regions have increased the likelihood of extreme flood events. Consequently, some existing spillways may no longer fully satisfy current design requirements. Therefore, the rehabilitation and modernization of hydraulic structures, particularly dam spillways, together with the enhancement of their hydraulic performance, have become important engineering challenges. Another critical issue is the high sediment load observed in many reservoirs located within the Amudarya and Syrdarya river basins. For this reason, sediment transport and deposition processes should be carefully considered when upgrading spillway systems. The discharge capacity of spillways can be improved through the application of specialized hydraulic structures. For example, labyrinth spillways are capable of increasing discharge per unit width; however, under conditions of high sediment concentration, they may promote sediment accumulation upstream of the structure. In this context, stepped spillways represent a promising alternative. Characterized by an inclined labyrinth-type configuration, these structures provide greater hydraulic efficiency than conventional linear spillways. Under identical head and width conditions, stepped spillways are capable of conveying significantly larger flow rates. This advantage allows reservoirs to operate at higher storage levels, increases available water reserves, and contributes to more efficient utilization of water resources. Their application is particularly beneficial in mountainous and topographically constrained areas where expanding spillway width is difficult or economically impractical. Previous investigations have demonstrated that the stepped spillway configuration improves hydraulic performance by reducing the upstream head over the crest and lowering the risk of overtopping. Although the magnitude of head reduction decreases slightly as discharge increases, the improvement remains substantially greater than that achieved by traditional rectangular spillways across all tested flow conditions.

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