清淤疏浚工程对七里海潟湖湿地水体交换的影响

Impact of dredging project on water exchange of Qilihai Lagoon wetland

七里海潟湖湿地受到人类活动的影响,湖盆淤积、湖面萎缩、水质恶化,其生态修复工程(一期)通过对湖盆进行清淤疏浚来改善潟湖生态环境.基于三重嵌套非结构网格建立七里海潟湖湿地水动力和物质输运数学模型,采用实测资料对模型的潮位、流速和流向进行验证,运用欧拉法计算潟湖整体滞留时间及其空间分布,分析工程对七里海潟湖水动力和水体交换的影响,结果表明:(1)工程对潮位的影响较小,工程后潮汐通道口门处涨落潮流量增大,涨落潮流速也随之增加;(2)工程后,潟湖纳潮量较工程前提升87%,滞留时间较工程前降低38%,水体交换能力自潮汐通道向潟湖内部逐渐减弱,工程对潟湖水体交换能力的改善主要集中在河道及潟湖中心水域;(3)工程前水体滞留时间的分布主要受到潟湖地貌影响,工程后水深增大,流场受地貌的影响变小,水体交换能力的分布主要受到潟湖流场影响.清淤疏浚工程有助于潟湖改善水体的交换能力和生态环境.

Caused by human activities,lagoon deposition,water area reduction and water quality deterioration of Qilihai Lagoon Wetland(QLW)become serious.Through the ecological restoration project of QLW(phase I),lagoon ecological environment will be improved by dredging project.Based on triple nested unstructured grids,the hydrodynamic and transport models of QLW were validated through observation data of tidal level,velocity magnitude and direction.Combined with the average residence time and the distribution of residence time in the whole basin calculated by Eulerian method and numerical simulation,the impact of dredging project on hydrodynamic and water exchange of QLW were analyzed.The results revealed that(1)the project had slight influence on tidal level,discharge and current speed during flood tide and ebb tide at the mouth of tidal inlet both increase after the dredging project;(2)the tidal prism of lagoon was increased by 87%after the dredging project,residence time was reduced by 38%,water exchange capacity was gradually weakened from tidal inlet to inner of lagoon and the main areas of water exchange improvement by the dredging project were water channel and center of lagoon;(3)the distribution of residence time before the project was mainly influenced by lagoon geomorphology,however,due to the water depth increases after the project,the flow field was less affected by geomorphology,and the distribution of water exchange capacity was mainly affected by the lagoon flow field.Improvement of water exchange capacity and ecological environment of QLW could be achieved efficiently by dredging project.