Canvey Island barriers spanning Benfleet Creek to the north and East Haven Creek in the west. The drainage system consists of sewers, culverts, natural and artificial dykes and lakes which feed seven pumping stations and gravity sluices that discharge the water into the Thames and creeks. Four of the discharge sites are "high flow" stations capable of discharging 600 litres of water per second at any tide level. The levels within the system are managed by a further five "low flow" pumping stations. The Environment Agency's Thames Estuary 2100 flood defence plan includes Canvey Island as one site for alleviating the flood
Yalu River its length. Most of the river freezes during winter and can be crossed on foot. The depth of the Yalu River varies from some of the more shallow parts on the eastern side in Hyesan (1 m) to the deeper parts of the river near the Yellow Sea (2.5 m). The estuary is the site of the Amrok River estuary Important Bird Area, identified as such by BirdLife International. About 205 islands are on the Yalu. A 1962 border treaty between North Korea and China split the islands according to which ethnic group was living on each island. North Korea