Terrain assessment, drainage and erosion - Geotechnical Investigation and Design Tables - page 191

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The greater slope lengths produce greater erosion potential. See Table 15.9.

Table 15.8 Landslide velocity scale (Cruden and Varnes, 1996).

Description Velocity

(mm/s)

Typical
velocity

Probable destructive significance

Extremely rapid Catastrophe of major violence; buildings

destroyed by impact of displaced material;
many deaths, escape unlikely.

5 10 3

5 m/second

Very rapid Some lives lost; velocity too great to permit

all persons to escape.

5 10 1

3 m/minute

Rapid Escape evacuation possible; structures,

possessions, and equipment destroyed.

5 10 1 1.8 m/hour

Moderate Some temporary and insensitive structures

can be temporarily maintained.

5 10 3 13 m/month

Slow Remedial construction can be undertaken

during movement; insensitive structures
require frequent maintenance work if total
movement is not large during a particular
acceleration phase.

5 10 5

1.6 m/year

Very slow Some permanent structures undamaged by

movement.

5 10 7

16 mm/year

Extremely slow Imperceptible without instruments;

construction possible with precautions.

Figure 15.1 Erosion and deposition process (Here from Bell, 1998, after Hjulstrom, 1935).