HKDSE Geography/M2a/Fluvial Morphometry

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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[edit]

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[edit]

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


This may appear in map-reading questions.

Drainage Pattern[edit]

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 Dendritic Drainage pattern.jpg Uniform rock structure (same type/resistance)
Rectangular Tributaries join at right angles (streams are not located at valleys) Rectangular.png Lines of weakness intersecting at right angles (perpendicular joint sets)
Trellis Tributaries join the main stream at right angles (streams are located at valleys) 175px 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 Radial.png At a hill (conical/volcano)
Centripetal Rivers flow from different directions towards central depression still needs one Inland basins