大通湖区水系连通工程改善水环境的效果评估

大通湖是洞庭湖区的重要组成部分,近年其水质状况呈现恶化态势,正通过实施水系连通工程,以期改善其水环境。基于MIKE21构建大通湖区水系连通工程的二维水动力-水质数学模型,选取总氮和总磷作为水质指标,模拟不同连通调度方案下大通湖的氮磷浓度变化,采用滞水区面积比例、浓度变化指数、换水率和水质浓度改善率,评估6个连通方案下大通湖水环境的改善效果。结果表明:通过实施引水调度方案能够有效改善大通湖水环境,当引水前期流量取30 m~3/s,出口水位控制在25.48 m时和引水后期流量保持为30 m~3/s不变,出口水位调整至25.88 m时,大通湖水环境改善效果最佳。本研究可为实施水系连通工程,改善类似湖泊水环境和提高引水调度效率提供参考。

Evaluation of improvement effect of the water system connection project on aquatic environment in the Datong Lake area

Datong Lake is an important part of the water system of Dongting Lake area. The water quality of Datong Lake has deteriorated in recent years, so the local government implemented a water system connection project in order to improve its aquatic environment. We established a two dimensional hydrodynamic-water quality numerical model of the water system connection project in Datong Lake area using MIKE21. Total nitrogen and total phosphorus were selected as the water quality indicators to simulate nitrogen and phosphorus concentration changes under six connecting and scheduling schemes. Then, the ratio of water stagnation area, concentration change index, water exchange rate and improvement rate of water quality were selected to evaluate the improvement effects of the six schemes. Results show that this water system connection project can effectively improve the aquatic environment of this lake through the implementation of the water diversion and dispatching plan. The improvement effect of the Datong Lake is optimal when the flow discharge is 30 m³/s and the water level at the outlet of Datongkou is controlled at 25.48 m in the early stage of the diversion, and the flow discharge in the later stage of diversion is main tained at water level at the outlet of the Datongkou is adjusted to 25.88 in the later stage of the diversion. This research can provide a reference for improving aquatic environment of similar shallow lakes and the efficiency of water diversion by implementing a water system connection project.