Changes of the bottom turbuence and flow structure by discrete freshwater discharge in the Yeongsan estuary, Korea

초록

Measurement of the water flow in the Yeongsan estuary, Korea, was made in August 2011, to investigate changes of flow structure and the bottom turbulence characteristics such as the Reynolds stress, turbulent kinetic energy (TKE) at the near bed (less than 35 cm above bottom). And comparison between the bottom TKE and suspended sediment concentration (SSC) was carried out to see how to link between the discrete surface freshwater discharge and the suspended sediment concentration near bed. Flow structure of horizontal component from the bed to 0.35 meters above bottom (mab) showed the upside-downed bell shape and maximum speed was less than 15 cm/s. However, vertical component was almost 1 cm/s in maximum, and showed peak at 0.1 mab and gradually decreased and then keep almost same magnitude. When the freshwater was discharged, the bottom flow rapidly responded by showing sudden change of direction. The magnitude of Reynolds stress was 2 cm^2/s^2 in maximum and TKE showed less than 10 cm^2/s^2 with upside-downed half bell shape. The stress and TKE component were directly responded by the surface freshwater discharging, and when the TKE was rapidly increased, the SSC was also increased in the bottom boundary layer, indicating that the active turbulent flow help suspending the bottom sediment. A hypothesis was suggested that the surface freshwater discharge by dam gate opening could increase the SSC of the bottom boundary layers by high turbulent flow activity.