Shift of estuarine type in altered estuaries

초록

An “altered estuary” is an estuary where the mixing of fresh and saltwater is influenced by a nearby estuarine dam. To better understand the alteration of the estuarine circulation caused by estuarine dams, four major Korean estuaries were classified according to the Hansen and Rattray’s stratification-circulation classification scheme. Among the four estuaries, the Han River estuary is the only natural estuary, while the other three estuaries (shallow microtidal Nakdong estuary, shallow macrotidal Geum estuary, and deep macrotidal Yeongsan estuary) are altered by estuarine dams. The stratification and circulation parameters were calculated for both discharge and non-discharge periods by using the tidally averaged salinity and velocity data observed from four Korean estuaries. The estuarine types of the altered Korean estuaries were compared with the previous results for the natural estuaries of similar magnitude in tidal range, water depth and discharge. By this comparison, the estuarine types of the altered Korean estuaries were found to be shifted from those of the natural estuaries. The controlling factors in determining the type in natural estuaries were tide, discharge and water depth while for altered estuaries they were the controlled river discharge and water depth. The different estuarine dam gate types with their different modes of operation (surface or bottom discharge) were also found to play an important role in the mixing and circulation of altered estuaries.