The Stratification and Circulation Characteristics of Estuaries Altered by Estuarine Dams

초록

An “altered estuary” is an estuary where the mixing of fresh and saltwater is influenced by a nearby estuarine dam. Such dams are situated in the transitional region where historically unhindered fresh water naturally diluted saltwater. However, the presence of estuarine dam led to freshwater discharge that is artificially controlled by humans. This in turn alte rs the processes and range of circulation of the natural estuarine environments, which has been studied by many scientists. The natural estuarine environments of the western coast of the Korean Peninsula are expected to be fully mixed estuary characterist ics, largely due to the (super) macro-tidal environment. In contrast, a micro-tidal estuary can be expected to be stratified more easily, especially when there is a small freshwater discharge. In this study, the Yeongsan and Nakdong River estuaries which contain estuarine dams are classified by the stratification-circulation diagram introduced by Hansen and Rattray (1966). Salinity data from CTD and Velocity data from ADCP is measured in each estuary are used to calculate two parameters of the diagram. These cases of estuaries whose water circulation are altered by estuarine dams are further compared with the Han River estuary, which is a natural estuary. Although exhibiting a large discharge in the summer, the relatively deep (~20 m) a nd macro-tidal (~4 m) Yeongsan River estuary was found to exhibit stratification due the release of freshwater along the water surface layer by the estuarine dam. Whereas, the Nakdong River estuary, which is shallow (~9 m) and micro-tidal (~1.5 m), was a fully mixed estuary because the gate of the estuarine dam is opened from the seabed. These results show that the design of the estuarine dam’s gate also affects the stratification and circulation characteristics of estuaries classified as altere destuaries.