HKDSE Geography/M2a/Fluvial Morphometry

Fluvial morphometry describes what rivers are shaped like. You don't have to know the word - it's just that a title was needed for this section.

Stream order

The stream order is counted from streams flowing from the source.

• When two first-order streams meet, they form a second-order stream.
• When two third-order streams meet, a fourth-order stream is formed.
• When a second-order stream meets a third-order stream, a fourth-order stream is formed.
• etc.

Drainage Density

Drainage density - Total length of channels in a basin over Total area of basin

This may appear in map-reading questions.

Drainage Pattern

A drainage pattern is the 'shape' of the river system. Usually, it suffices to be able to identify each. The formation of each pattern is included, just in case.

Name	Description	Image	Formation
Dendritic	Looks like tree branches; tributaries join at acute angles		Uniform rock structure (same type/resistance)
Rectangular	Tributaries join at right angles (streams are not located at valleys)		Lines of weakness intersecting at right angles (perpendicular joint sets)
Trellis	Tributaries join the main stream at right angles (streams are located at valleys)	File:Trellis drainage pattern.JPG	Alternate layers of resistant and non-resistant rock (soft rocks are eroded to form valleys and thus tributaries)
Radial	Rivers flow in all directions from a centre down the sides of a hill		At a hill (conical/volcano)
Centripetal	Rivers flow from different directions towards central depression	still needs one	Inland basins