Normally, river flows much below bankfull stage; abnormally; however, bankfull, stage may be crossed when river is said to be in a flood stage.

Waterfalls are magnificent jumps made by a stream or river water at certain specific parts of ir course where re is a sudden and considerable drop in gradient of channel.

Attrition is term used for term for wear and tear of load sediments being transported by a moving natural agency through process of mutual impacts and collisions which y suffer during ir transport.

Continental shelf is gently sloping land part that remains partly submerged under seawater. It may be only a narrow strip or quite an extensive area stretching for hundreds of kilometres.

Coral reefs are peculiar types of ridge-like marine deposits that have been formed due to accumulation of dead parts of certain of sea-organisms.

Hydraulic action is mechanical loosening and removal of material from rocks due to pressure exerted by running water. The higher velocity, greater is pressure of running water and hence greater is its capacity to bodily move out parts of rock.

Deltas are defined as alluvial deposits of roughly triangular shape that are deposited by major rivers at ir mouths, i.e., where y enter a sea.

An atoll is essentially an annular, circular or semi-circular coral reef surrounding a central body of water that is as usual called a lagoon. In a typical atoll, ring made of coral deposits may be continuous or discontinuous, more often broken at places.

Potholes are variously shaped depressions of different dimensions that are developed in riverbed by excessive localized erosion by streams.

Three conditions necessary for formation and growth of a delta are: absence of any strong sea currents; presence of good quality of load in stream and slope of seashore where stream enters seawater must necessarily be quite gentle and wide.