2. Drainage Density

Drainage Density

The total length of all streams per unit area of a drainage basin. Formula: Total length of streams (km) ÷ Total area of drainage basin (km²). Answer is in km/km².

How to calculate drainage density

Formula: Total length of all streams (km) ÷ Total area of the drainage basin (km²). Example: 120km ÷ 30km² = 4km/km² (meaning 4km of river for every km²).

Effect of high rainfall on drainage density

High rainfall → more runoff → HIGHER drainage density.

Effect of high evaporation on drainage density

High evaporation → less runoff → LOWER drainage density.

Effect of high infiltration on drainage density

High infiltration → less runoff → LOWER drainage density.

Effect of rock hardness on drainage density

Softer rocks → channels form more easily → HIGHER drainage density. Harder rocks → lower drainage density.

Stream Order 1

The smallest streams where rivers begin. Narrow, clean water, steep gradient, V-shaped valley, downward (vertical) erosion. Found in mountains.

Stream Order 2

Wider than order 1, water becomes dirtier, less steep gradient, valley begins to widen, lateral erosion, greater water volume.

Higher Stream Orders (3, 4, 5+)

Fewer streams per order, streams become wider (more lateral erosion and deposition), gradient becomes more gradual, water becomes dirtier. The highest order river flows into the ocean.

What does a higher drainage density mean?

There are more streams per km² — the area has more runoff (e.g. due to high rainfall, hard rocks, or low infiltration).

Drainage basin

The area of land drained by a river and all its tributaries.

Draingage Density and Hydrograms ( Graph )

Discharge and Hydrographs ( Graph )