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

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.