The goal of WP2 was: (1) To review and compile the range of existing technical, biological, and organizational countermeasures against Extremely Rapid Mass Movements;
(2) to elucidate the effectiveness of these measures and to highlight their
maximum protection potential against a process or a combination of the
processes considered; and (3) to propose recommendations for the future
installation and implementation of countermeasures.
One of the results of WP 2 is a comprehensive dictionary describing the countermeasures commonly used with diagrams and photos. The description includes the purpose of the measure, the design criteria, the effectiveness and the cost for each measure.
In general, there are a series of alternatives for reducing a risk:
1. Land-use planning and legislation in long-term planning
2. Relocation of the endangered goods
3. Use of non-physical measures: establishing emergency plans and procedures, forecasting hazards, and temporary evacuation and closure
4. Use of physical protection measures
Physical measures can be divided into three main categories depending on their location:
• Measures in the starting zone where the main purpose is to stabilise the sliding material and reduce the possibility of release;
• Measures in the path where the main purpose is to reduce entrainment, brake the velocity or deflect the sliding material;
• Measures in the run-out zone where the main purpose is to stop or deflect the sliding material, or to reinforce the element at risk to withstand the forces.
When discussing preferable alternatives, the optimal solution should be sought both for the people directly exposed to the hazard, and for the local community and country as a whole. The reduction of risk and the increase in safety
obtained by each of the methods must be compared to the total cost of their implementation by:
• Determining cost/risk functions
• Determining benefit/risk functions
• Calculating the net benefit
• Selecting the maximum net benefit solution
All direct and indirect costs and benefits must be taken into account in cost/benefit analyses. Other factors may also need to be considered, e.g. political prioritising, social-psychological or cultural heritage aspects.
It should also be kept in mind that reducing natural hazards and risks may include conflict between experts, the political authorities and the people directly exposed to the hazard. Experts may regard the hazard differently from the local people exposed to the hazard and may therefore present solutions to reduce risk which are not acceptable to the people involved, or to the politicians. Therefore communicating risk, in order to create a shared perspective about the situation and the measures to be envisaged, plays a vital role, in the risk management process.
Non-physical measures are preferable as a temporary means of risk reduction for infrequent processes and for low-risk objects like roads. In general, temporary mitigation measures are superior to structural measures if hazards are: a) infrequent, or b) spatially fuzzy and thus difficult to predict. On the other hand, structural measures are superior if: a) the hazard is known, delimited and frequently returns, b) the stakes at risk are high and failure to mitigate the risk will have large consequences, and c) it is foreseeable that the measure will be useful for its whole lifetime.
For residential areas, non-physical measures are often used as preliminary solutions until permanent physical measures are in place or as an additional measure to reduce the residual risk.