Computational hydrodynamic aspects of engineering solutions ensuring the determination of technical water use under conditions of stable stratification

Abstract

Hydraulic regulation is based on the operational management of water levels and flows. A basic, though far from perfect, approach to such measures is the technology of forced reservoir flushing timed to coincide with the peak natural inflow that is the spring flood. The classic approach here involves preemptively lowering the water level to the minimum permissible mark (dead volume level), followed by passing floodwaters over the spillway. Theoretically, such a mechanism should ensure the removal of polluted water from near bottom horizons. However, in practice, the effectiveness of this method for the conditions of Verkhne-Zyryansky hydroelectric complex, is significantly reduced due to the design features of the spillway. The structure is equipped with a shaft spillway, the threshold of which is located at an elevation close to the normal headwater level (NHL). As previously established, under conditions of stable density stratification, the most mineralized layers are localized in the bottom layer. With the existing spillway design, water masses forming in the surface and intermediate horizons are flushed out. As the spillway passes, the freshest waters of standard quality are discharged into the tailwater, whereas the deep, highly mineralized waters, which pose the greatest threat to a sustainable industrial water supply, remain hydraulically trapped in depressions in the bottom relief and continue to accumulate. The traditional flushing method results in an inefficient use of flood potential, as it fails to reduce the overall mineralization of the withdrawn water. A fundamentally different approach to solving the problem, enabling the elimination of the aforementioned design flaws, is the paradigm of selective water drainage. The most promising and technologically sound implementation of this concept is the construction of a specialized siphon-type flood spillway designed to drain highly mineralized waters from the deepest zones of the reservoir.  In this work, a numerical model was developed and a series of computational experiments were conducted to refine engineering solutions for ensuring a sustainable technical water supply under conditions of significant stratification of water masses.