Research on improvement effect of discharged water temperature from Wudongde Reservoir under stoplog gate operation

Selective withdrawal strategy is an effective measure for alleviating low-temperature water discharge from reservoirs.Clarifying the downstream transmission and hysteresis patterns of selective withdrawal strategy effects from upstream reservoirs to downstream reservoirs in cascade reservoir systems is of great significance for establishing a joint water temperature regulation system.A two-dimensional hydrodynamic water temperature mathematical model of the Wudongde Reservoir was employed using the CE-QUAL-W2 model in this study, and based on the 2022 scheduling process, two scenarios of single-layer water intake and designed stoplog gate operation were set up.The impact of stoplog gate on the water temperature regime of Wudongde Reservoir and its downstream attenuation characteristics were quantitatively analyzed.The results show that the stoplog gate operation could significantly raise the position of the flow layer, increasing the average water intake elevation from 935.10 m to 952.20 m, promoting the mixing of surface water bodies, and resulting in a maximum reduction of 2.3 ℃ in vertical temperature difference under the designed stoplog opration scenario compared to the single-layer intake scenario.Under the designed stoplog opration scenario, the discharged water temperature increased by an average of 0.5 ℃ compared to single-layer water intake, with an average improvement of 0.1~1.0 ℃ over ten days.Due to the regulation and storage effects of downstream cascade reservoirs, the effect of stoplog gate in Wudongde Reservoir has significantly declined along the way, with an average improvement range from 0.49 ℃ to 0.16 ℃, and a maximum improvement effect decrease of 1.01 ℃.The effective manifestation times at Baihetan Reservoir, Xiluodu Reservoir, and Xiangjiaba Reservoir lagged by 16, 53, and 62 days, respectively.The research results can provide a scientific basis for optimizing the selective withdrawal scheduling strategy of cascade reservoirs and ensuring basin-scale ecological water use security of the basin.