Mitigation of the Landslide

Effects of Landslide
1. Loss of human life
2. Economic losses (both direct and indirect)
3. Environmental impacts

As can be seen from the picture, there was most probably a loss of human life, along with possible financial losses in terms of direct and indirect costs. The impact to the environment can be seen as minimal and will not be discussed at length.

As we are aware of the causes of landslides, as can be read from the below entry on the Causes of Landslides, what steps can be taken to reduce the hazardous impacts of landslides? We will now explore the possibilities of how to mitigate a landslide.


Management of Landslide Hazards
1. Hazard Mapping and Zoning

A landslide hazard map is constructed by conducting extensive engineering surveys of the characteristics of a chosen slope, together with evidence of past landslide activity (which can be found in the form of distinctive deposits and geologic structures). The finished maps indicate those areas which are at greatest risk from landslides and if used properly in the planning process, should serve to reduce the landslide hazard by keeping people away from the most vunerable slopes; or by taking steps to stabilize the slope in the attempt to prevent the a disaster.

Aerial photography has been used extensively to produce landslide inventory maps; but air photos are not readily available in all areas. Scientists increasingly rely on global satellite data to help assess the risk for potential landslides.

A possible reason why the landslide shown in the photo below had not been predicted and the people evacuated, could be that the town could not afford to hire professionals to examine the slope. Such services are expensive and require considerable technical expertise, and require planners to respond appropriately to their findings, which is not always the case when pressure for development is high. Urban sprawl onto marginal hillsides in some cities because of the short-term demands for housing and land outweigh the possible problems associated with a landslide, which, of course, might never happen.

2. Modifying the Event

Slope/Cliff Pinning
This could have been a possible method of preventing the landslide from occurring. The way this is done, is by pinning the cliff through the likely shear planes in the cliff. Piles, made up either of metal, plastic of wood are used to pin the sheared block which seems to be unstable and vunerable to potential mass movement. Toe revetments are often built at the foot of the cliff to provide toe support.

This method is relatively inexpensive and if the potential shear plane was effectively identified, the landslide could have been altogether avoided.

However, the downside to cliff pinning is that it can further disturb the cliff materials and at times could accelerate the process as the materials of the slope become less compacted with the intrusion of foreign materials. Also, identification of potential shear planes can prove to be a difficult task.


Slope Drainage
This is the cliff-face method of control which is most widely used in the UK, particularly for cliffs with high clay content. The way it works is that pore water pressures are reduced by drainage lines within the cliff face, field drains and gravel trenches. Overland flow is intercepted by shallow surface drains and vertical drainage removes water from the cliff face as well as the body of the cliff.

The landslide in the photo could have been avoided using this method, as the abundance of foilage on the slope and the surrounding area suggest moderate rainfall - which can be enough to trigger a landslide with a little help from other factors.

3. Modifying the Vulnerability

Public awareness and Education
Achieving widespread awareness of landslide hazards will enable communites and individuals to make informed decisions on where to live, purchase property or locate a business. Local decision-makers will know where to permit construction of residences, business and critical facilities to reduce or zero potential damage from landslide hazards.

If the community which was affected in the photo knew that being at the base of a slope which had a road cut into its side, and possibly had some of its essential toe support removed, would increase the possibility of a landslide, they would most definitely have moved out and away from the base of the slope.