Abstract:

Tianfumiao Reservoir is located in the eastern branch of the Huangbai River Basin. It is a water source in the town of Leizu, Yichang City. The water quality of the reservoir has deteriorated since 2015 owing to the influence of the surrounding phosphate mining. Therefore, the Yichang municipal government has implemented an ecological and environmental dredging project for the river channel in the Tianfumiao reservoir area. During the implementation process, it was found that the suction head of the dredging equipment during dredging ship operation caused disturbances to the surrounding water body and sediment, which may have caused secondary pollution of the reservoir water body. To explore the sediment disturbance caused by the dredging process, this study used laminar flow and dilute matter transfer modules in COMSOL Multiphysics to establish a phosphorus release model for reservoir sediment pollutants. Based on the attribute data of water quality and dredging equipment of Tianfumiao Reservoir, and the empirical values summarized by predecessors, the diffusion velocity distribution characteristics of sediment and the release law of phosphorus pollutants in reservoir sediment and pore water were simulated under different dredging times and different horizontal disturbance ranges in the process of dredging disturbance. The reliability of the model was verified through field simulation sediment disturbance experiments. The simulation and experimental results showed that when the dredging disturbance time increased, the sediment and its pollutants gradually diffused to the water surface and the diffusion rate and pollutant concentration increased with time. Under the same dredging disturbance time, the vertical diffusion of resuspension and phosphorus pollutants was affected by the horizontal disturbance range. The larger the horizontal disturbance range, the more sediment diffused to the water surface, the more phosphorus pollutants were released from the sediment, and the greater the harm to the water environment quality of the reservoir. In the early stages of release, the concentration of pollutants in the water increased sharply, and the release of phosphorus pollutants into the pore water played a leading role. Subsequently, the concentration of the pollutants in the water increased slowly. In the later stage, the resuspension gradually mixed evenly, and the difference in total phosphorus concentration on the vertical line decreased. The release of pollutants into the sediment reached equilibrium. The results showed that the model can reasonably predict the change in total phosphorus concentration in water caused by dredging disturbances and provide a scientific basis for preventive measures for dredging engineering practices of lake-type deep-water reservoirs.

Key words: COMSOL Multiphysics, Tianfumiao Reservoir, dredging disturbance, sediment phosphorus pollutants, diffusion model, concentration distribution

摘要：

天福庙水库处于黄柏河流域东支，是宜昌市嫘祖镇的水源地，受周边磷矿开采的影响，2015年以来水库水环境质量不断恶化，为此宜昌市政府对天福庙库区河道实施了生态环保清淤工程。实施过程中发现，清淤船作业时清淤设备吸头会对周边水体及底泥造成扰动，进而可能会对水库水体造成二次污染。为了探究清淤过程导致的底泥沉积物扰动情况，利用COMSOL Multiphysics中的层流和稀物质传递等模块建立水库底泥污染物磷释放模型，基于天福庙水库水质和清淤设备的属性数据，以及前人总结的经验值，模拟清淤扰动过程中不同清淤时间和不同水平扰动范围下底泥的扩散速度分布特征，以及水库底泥和孔隙水中的磷污染物的释放规律，并进一步通过实地模拟底泥扰动实验验证模型可靠性。模拟和实验结果表明：当清淤扰动时间不断增加，底泥及其所含的污染物会逐渐向水面扩散，扩散速度和污染物浓度会随时间的推移而不断增大；在同一清淤扰动时间下，再悬浮液和磷污染物的纵向扩散受水平扰动范围的影响明显，水平扰动范围越大，底泥向水面扩散越多，底泥磷污染物释放浓度越多，对水库水环境质量危害越大。释放初期，水体中污染物浓度增加较为剧烈，孔隙水中的磷污染物释放起主导作用；随后水体中污染物浓度增加速度变缓，后期再悬浮液逐渐混合均匀，垂线上的总磷浓度差距减小，底泥中污染物的释放达到平衡状态。研究发现模型能够对清淤扰动造成的水体总磷浓度变化进行合理预测，为湖泊型深水水库清淤工程实践的防范措施提供了科学依据。

关键词: COMSOL Multiphysics, 天福庙水库, 清淤扰动, 底泥磷污染物, 扩散模型, 浓度分布