岬湾海岸海滩养护工程对水体交换的影响

Influence of Beach Nourishment Project on Water Exchange in Headland-bay Coast

摘要:

岬湾海岸内岬头后侧水动力条件较弱容易造成水体生态环境退化，水环境改善可归结为控制污染物，而水体交换能力的强弱反映了水体自净能力.采用MIKE 21 软件建立潮流和保守物质输运模型对人工岬湾内部进行分区研究，引入时间尺度指标定量分析水体交换对海滩养护的响应.由于海滩养护工程中沙坝与水流走向保持基本平行，沙坝修建后使得岬头后侧环流减弱，沙坝坝顶处流速增加，两沙坝间通道流速减小.滩肩前方海域流速减小，两沙坝后侧的流速减少更多.人工岬头与沙坝之间形成潮汐通道使得靠近岬头处流速有所增加，工程后滞留时间缩短；其中岬湾内近岬头的2个子区域滞留时间减少量较多，岬湾内中部区域滞留时间变化不明显.波浪和风场均会促进水体交换，但由于波浪受到风场影响，波浪和风场共同作用下滞留时间并不为单独条件的线性叠加关系.

Abstract:

The hydrodynamic conditions at the back of headlands in a headland-bay are relatively weak, which may be easy to cause deterioration of water ecological environment. The water environment can be improved by controlling the destination of pollutant, hence the capacity of water exchange reflects waterbody self-purification capacity. MIKE 21 is employed to establish tidal current and conservative mass transport model, in which the headlandbay coast is divided three sub-regions, and the time-scale quantitative measurement is introduced to discuss the responses of water exchange to the beach nourishment project. Due to the orientation of sandbars in the beach nourishment project is basically parallel to the main direction of current, the circulations in the back of headland are weakened, and the velocity increases at the top of the sandbars while decreases between the two sandbars. The velocity decreases in front of the berm and decreases more in the back of sandbars. The increased current velocity in the tidal inlet between artificial headland and sandbar shortens the residence time after the beach nourishment project. The reductions of residence time in the two subregions around the headlands are much larger than that in the middle sub-region. Both wave and wind promote water exchange. However, because wave is also affected by wind, the residence time under both wave and wind conditions is not equal to the linear superposition of residence time under wave condition and wind condition respectively.