Nonlinear variation of discharge coefficient and energy dissipation optimization for bottom outlet of EG reservoir: an integral hydraulic model study

> 0.99) was derived for real-time discharge prediction. This study provides a systematic quantification of the U-shaped nonlinear evolution mechanism of the discharge coefficient with gate opening for the radial-gated bottom outlet of the EG Reservoir and quantifies the discharge deviation amplitude (up to approximately 21%) in the hydraulic sensitive zone (G = 2.0-3.0 m). To mitigate the hydraulic instability exacerbated by these discharge fluctuations, the stilling basin geometry was optimized by deepening the apron (from 5.0 m to 7.4 m) and raising the end sill. This geometric optimization transformed the flow regime from an unstable swept-out jump to a stable submerged jump, increasing energy dissipation efficiency from 46.3% to 64.5% under design flood conditions. These findings establish a quantitative framework for refined gate operation protocols and resilient energy dissipation design, with the correction model applicable for gate openings G = 0.96-4.80 m (R² > 0.99) under the tested geometric conditions, and demonstrated downstream scour reduction of 35-40%.