Tidal current ridges

widely distributed geomorphological phenomena over the continental shelf of the world

are studied. They are formed by tidal current and the trend of their sand bodies runs parallel to the direction of tidal current. There are two types of the plane shapes: the parallel and the fingered. Conditions of forming tidal current ridges are the velocities of tidal current ranging from 1 to 3.5 knots and the supply of abundant sediments. Tidal current ridges often develop in following morphological locations: the bays

estuaries

the mouths of channels

as well as the offshore area with strong tidal current. Tidal current ridges occur generally at a water depth of less than 35 metres. The sediments of tidal current ridges are mainly composed of sand. The grain size of the sediments is uniform and well sorted. The characteristics of grain size of the sand imply that their formation mechanism is similar to that of river sand

that is

both of them are the result of flow movements in a trongth channel controlled by boundary. There is however difference between them that the river sand is formed by one-way flow movement while the tidal current sand by two-way movement. There are two saltation populations in the log-probability curves of tidal current sand

the sorting of first saltation population is better than the second one

and having positive skewness

which differs from beach sand. In the C-M grain size pattern tidal current sand is most found in graded suspension segment. The continental shelves of the Yellow Sea

the East China Sea and the South China Sea have favourable conditions for developing tidal current ridges in massive scale and special shape

such as the tidal current ridges in the offshore of Jiangsu

the Gulf of Korea

the shoal of Liaodong

the east and west mouths of the channel of Qiongzhou

Jiaozhou Bay

the shoal of Taiwan

Lingdingyang

the north branch of Changjiang estuary. The studies of them are of vital significance in shipping

fishing

submarine engineering

military installations

oil and gas explorations

as well as in scientific research.