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洪水条件下河道型水库流场与水温结构的三维数值模拟
Three-dimensional Numerical Simulation of Flow Field and Water Tem-perature Structure in Channel-type Reservoirs under Flood Conditions
掌握洪水条件下水库流场和水温结构的动态变化对于水质管理和生态安全至关重要。以河道型水库BLH水库为典型案例,基于Delft3D模型建立了三维水动力水温模型,使用水体相对稳定度(RWCS)量化水温结构,分析了不同洪水条件下的流场和水温特征。坝前和库中心表底层水温模拟的决定系数R2分别为0.989和0.982,模型效果良好。结果显示,水温结构受水流形态和流速影响,入库流量增加会降低水库RWCS/H,削弱水温分层;受洪水影响从河流区到湖泊区温跃层厚度逐渐增加,随入库径流增大各区温跃层占水深的比值呈现下降的趋势。洪水对水库温跃层的影响从库尾到坝前逐渐减弱。径流越大其潜入库区的位置越往下,水体扰动越强,水体热分层结构破坏程度越大,垂向水温分布会趋于一致。
[Objective] This study aims to provide theoretical support and technical basis for ecological regulation and water quality safety management of reservoirs during flood season by revealing the coupling disturbance mechanisms of different flood processes on the flow and thermal structures in different reservoir zones. [Methods] Taking the BLH Reservoir, a typical channel-type reservoir of northern China, as an example, a three-dimensional hydrodynamic-thermal model based on Delft3D was developed by comprehensively inputting measured reservoir topography, hydrological, and meteorological data for modeling, calibration, and validation. The model’s accuracy was evaluated using water level and water temperature data of a typical flood year from January to December. Four flood inflow scenarios (S1-S4, with peak discharges of 7 487, 6 150, 4 743, and 2 670 m3/s, respectively) were designed to analyze flow velocity, thermocline thickness, and thermal stratification responses. The RWCS/H index was used to assess the intensity of thermal stratification and its spatiotemporal variation trends. [Results] 1) Model validation showed that the water level simulation had an R2 of 0.995, the water temperature in front of the dam had an R2 of 0.989, the water temperature at the reservoir center had an R2 of 0.982, indicating high adaptability of the model in capturing the spatiotemporal responses of hydrodynamics and thermal structure. 2) Under flood conditions, significant variations in flow field structure were observed, particularly in the lake zone where a pronounced vertical velocity gradient formed. During flood peak stages, the flow velocity in the bottom layer increased from 0.008 m/s to 0.078 m/s, reflecting the enhanced disturbance of subsurface flow on vertical thermal exchange. The vertical water temperature structure showed that as inflow volume increased, the surface-bottom temperature differences across all zones decreased, and thermal stratification became weaker. Under the extreme S1 scenario, the thermocline in the river zone was completely disrupted, with the temperature difference dropping to 0.29 ℃ and RWCS/H decreasing to zero, resulting in nearly uniform vertical water temperatures. RWCS/H in the transition and lake zones declined markedly, reaching minimum values at 70 h and 100 h after the flood peak, respectively, demonstrating a spatial propagation lag in flow-induced disturbances. 3) Furthermore, under high flood conditions, density currents penetrated deeper into the water body, generating large-scale disturbances that significantly weakened thermocline stability. This intensified bottom sediment disturbance and elevated the risk of pollutant release. [Conclusions] The three-dimensional hydrodynamic-thermal numerical model established in this study demonstrates good capabilities in simulating and predicting hydrothermal dynamics in channel-type reservoirs under flood conditions, accurately capturing the water temperature response processes influenced by density currents. The greater the flood intensity, the more thoroughly the water temperature stratification is disrupted, the more concentrated the flow channels become, and the more homogenized the water temperature structure tends to be. The RWCS/H index effectively reflects the intensity of thermal stratification disturbances and reveals their spatial differences and propagation lag characteristics. This study, for the first time, systematically quantifies the coupling variation patterns of flow fields and water temperature structures in channel-type reservoirs under different flood magnitudes, filling a gap in related researches. The findings provide scientific support for reservoir ecological regulation, water quality prediction, and disaster prevention decision-making, particularly applicable for managing sudden flood events under extreme climate conditions.
洪水条件 / 水库流场 / 水温分层 / 三维数值模拟 / 时空动态特征
flood conditions / reservoir flow field / water temperature stratification / three-dimensional numerical simulation / spatiotemporal dynamic characteristics
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