1. Drainage Patterns

Drainage Pattern 

The arrangement of streams in an area, determined by the underlying rock type, structure and relief of the land.

Dendritic Pattern

A tree-like drainage pattern that forms on flat or gently sloping land with massive igneous or horizontal sedimentary rocks of similar hardness. Looks like branches of a tree.

Trellis Pattern

Forms on inclined strata that are unequally resistant to erosion. Develops in areas with parallel fold mountains. Shorter tributaries join the main stream at RIGHT ANGLES. These streams often cut poorts/gaps through mountains.

Rectangular Pattern

Forms on igneous rocks that have joints and cracks. Streams develop right-angled bends where the joints meet. Example: Zambezi River at Victoria Falls.

Centripetal Pattern

All streams flow INWARD toward a central low-lying area or pan. Example: Okavango, Botswana.

Centrifugal / Radial Pattern

Streams flow OUTWARD from a central high point (e.g. a volcano or dome). Example: Kilimanjaro.

Parallel Pattern

Develops on a surface that slopes uniformly and is fairly steep. The river and its tributaries flow downslope nearly PARALLEL to one another.

Deranged Pattern

Develops on land that was previously covered by an ice sheet or glacier. No apparent/clear drainage pattern. Landscape has small streams, swamps and lakes. Example: Grootpan, Brandvlei, Verneukpan (Northern Cape).

What rock type causes a dendritic pattern?

Massive igneous rocks OR horizontally-lying sedimentary rocks — rocks of similar hardness.

What rock type causes a rectangular pattern?

Igneous rocks with joints and cracks (e.g. at Victoria Falls on the Zambezi River).

What is the key feature of a trellis pattern?

Shorter tributaries join the main stream at RIGHT ANGLES, and these streams often cut poorts (gaps) through the mountains.

What is a poort?

A gap or pass cut through a mountain ridge by a river, common in trellis drainage patterns.