Global inventory of closed-off Tidal basins and developments after the closure

Closed-off tidal basin reclamation represents a special type of reclamation. In several countries enclosing dams have been built to close off estuaries, shallow seas, or lagoons, and lands up to 5~6?m - MSL (below mean sea level) have been reclaimed in the former tidal basins. Although these areas were generally primarily reclaimed for agriculture, a second-stage development may have taken place where parts of these lands were transferred to urban and industrial use. The originally saline water in the created reservoirs was transformed to fresh water that may be used for irrigation, domestic and/or industrial water supply. In several of these reservoirs there are water quality problems, primarily due to pollution in upstream parts of the river basins. In 2007 the Enclosing Dam of the Zuiderzee Scheme in the Netherlands had existed for 75?years. This occasion was used to conduct a global inventory of closed-off tidal basin reclamation on which this paper is based. The study shows that closed-off tidal basin reclamation concerns 25 schemes with a total area of 738 000?ha, of which 337 000?ha have been reclaimed and 401 000?ha freshwater reservoirs have been created. This paper presents a summarized overview. Attention is paid to safety, land use and changes in it, development of water quality in the reservoirs, as well as to land subsidence and possible impacts of climate change, like rise in mean sea level. In time this may have implications for safety of the deep polders, the management of the reservoirs as well as for the sustainable development of tidal areas in the future. These items are presented for four major tidal reclamation schemes: the Zuiderzee Scheme in the Netherlands, the Saemangeum Scheme in South Korea, the Kuttanad Region in India and the Hachirogata Scheme in Japan