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Mitigation measures

Site-Specific Mitigation Measures: In view of the widespread fatal landslide incidences, it is necessary to adopt suitable mitigation measures to minimize the devastating effect of landslides. Various site-specific remedial measures can be adopted after a detailed examination of the site conditions, as suggested below:

1. Proper drainage management: Water infiltration in the overburden during heavy rains and consequent increase in pore pressure within the overburden reduces the strength of the material and causes sliding of the landmass. This can be minimized by reducing infiltration by providing adequate drainage network. In this regard, a dual-pronged strategy must be adopted such as reducing flow of water into the vulnerable slope material by constructing interceptor drain, trench drain, diverting side drains and by channelization of all drains and second, by draining out the remaining water by horizontal to sub-horizontal drainage system (using perforated pipes) including construction of collection chamber and diverting the water to existing channel and removal of any blockade to existing drainage system. Most important, all drainage systems need regular maintenance and surveillance for detecting any change in the flow pattern or pore water pressure by installing inexpensive piezometers at selected locations.

2. Bio-engineering and Afforestation: It is a well-understood fact that tree cover largely increases the stability of the underlying ground by increasing root strength, intercepting direct effect of precipitation and reducing pore water pressure by evapotranspiration. Therefore, bio-engineering methods including that of large scale afforestation and protection of existing vegetation cover needs to be adopted in the landslide-prone areas. The selection of suitable plant species should be such that can with stand the existing hydrological conditions of the terrain.

3. Early Detection: Early detection is the key to any effort towards minimizing loss and implementing remedial measures. As landslides normally occur in far-flung areas, wherein local population is first to witness and face consequences, it is imperative that they should be made aware of the slope conditions and some of the natural phenomena which precede major landslide events.

4. Slope stability measures: In addition to all suggested measures related to proper drainage management to reduce pore water pressure, structural measures need to be adopted after detailed investigation of the site. These measures include providing buttresses, shear keys, sub-drains, soil reinforcement, surface protection, slope modification, retaining walls, gabion wall, breast wall, etc.

Landslide Hazard Mitigation Programme

In order to prevent and mitigate the landslide risk, national initiatives are required or strengthened to address the following aspects:

1. Landslide Hazard Zonation (LHZ): LHZ at different scales, i.e. starting from country scale, regional scale to site-specific scale serves various purposes as per the intended application. Recent advances in data acquisition techniques based on remote sensing as well as ground-based instruments provide ample data that can be processed, modeled and analysed using statistical as well as deterministic modeling techniques in GIS and prepare the quantitative landslide hazard zonation maps.

2. Mapping and monitoring of active landslides/vulnerable slopes: Mapping and monitoring of active landslides as well as vulnerable slopes and associated potential danger such as landslide blockade lake formation can contribute immensely in any effort related to landslide hazard mitigation. In this regard field investigation, mainly related to early detection and earth observation techniques can play a significant role, particularly in inaccessible areas, where physical monitoring is not possible nor very cost effective. Early detection not only averts disaster, but also requires low-cost remedial measures for stabilizing the slope.

3. Early Warning Systems: As landslides are very localized and confined to intense monsoon periods, it is envisaged that an early warning system would provide immense benefit in alerting people living in high hazard areas. Therefore, efforts should be made to develop and install early warning system in landslide prone areas.

4. Awareness generation: Experience has shown that a high level of awareness and proper communication with local population can avert disaster due to landslide. It is important to take up awareness programmes in the hazardprone areas to apprise local population and all stakeholders about the landslide risk in the region, possible causes of landslides, preventive measures (including bio-engineering methods), early detection and monitoring methods as well as remedial measures. It is important to generate awareness at various levels starting from school to college level through media campaigns, development and distribution of leaflets and posters, meetings, seminars, workshops on a regular basis.

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