Numerical assessment of wind-induced destratification and its implications for water-quality management in Lake Oberon, Australia

Résumé fourni par la source

Thermal stratification regulates vertical mixing and biogeochemical exchange in drinking-water reservoirs, and its persistence can increase hypolimnetic isolation and associated water-quality risks. Although the fundamental mechanisms of wind-driven mixing are well established, reservoir-specific quantitative relationships among wind speed, forcing duration, direction, and stratification response remain poorly constrained, particularly in temperate Australian drinking-water reservoirs. This study applied the three-dimensional Aquatic Ecosystem Model (AEM3D) to quantify wind-induced weakening of thermal stratification in Lake Oberon, New South Wales, Australia. A baseline hydrodynamic simulation was developed for August 2023–July 2025 using observed meteorological forcing, reservoir bathymetry, inflow conditions, and operational outflows. The model was calibrated against water-temperature observations from August 2023 to February 2024 and independently validated using observations from March 2024 to July 2025 that were excluded from parameter adjustment. Controlled wind scenarios were subsequently applied during peak summer stratification to isolate the effects of wind intensity, duration, and direction-dependent effective fetch. Wind forcing reduced the surface-to-bottom temperature difference by 0.20–1.28 °C, while maximum mixing efficiency and destratification efficiency reached 25.6% and 26.0%, respectively, demonstrating substantial but incomplete erosion of stratification. For the 18 km h −1 scenario matrix, wind duration explained around 86.7% of the variation in thermal-response metrics, compared with about 10.8% for wind direction. One-day events primarily displaced the upper thermocline, whereas three- and five-day forcing produced progressively greater thermocline adjustment, reductions in Schmidt stability, and delayed hypolimnetic warming. The Wedderburn Number provided a link among wind stress, stratification strength, epilimnetic depth, effective fetch, and thermocline displacement. These findings demonstrate that cumulative forcing duration and basin orientation exert stronger controls on stratification weakening than wind speed alone and provide scenario-derived operational indicators for post-wind water-quality monitoring and adaptive reservoir management.

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