avalanche Ciwidey

News landslide in Kampung Bali, Village Tenjolaya, Pasir Jambu, Ciwidey, Bandung regency, reminding us of the landslide in Kampung Walahir, Pananjung Kidang Village, District Cililin nearly six years ago. At that time, the landslide in Kampung Walahir be disastrous fairly large, with 15 casualties, 21 houses buried and damaged 22 other houses mild to severe brunt avalanche of material. It made President Megawati Soekarnoputri took time to review the disaster site.

Similarly, the catastrophe in Kampung Dewata. This disaster not only attention and make the people of West Java surprised, but almost all people in the homeland. At least 45 people became victims and about 27 houses and six other public facilities building material hit by the avalanche. Over this incident, Vice President Boediono took time to review the disaster site.

Are there similarities between both these landslides? Both have the same type and characteristics are loosened component material flow (debris flow) consisting of area avalanche of material resources, flow paths, and the depositional area.

Landslide in Ciwidey, originated from a very steep slope, and came upright and located at the very top of the soil erosion of the body. This place is the main source of the landslide material (source area), which is composed of soil residual result of weathering of volcanic breccia, mixed with a variety of vegetation growing on it. Crown of avalanches that seemed to form an arch with a width of up to thirty meters and very steep escarpment up straight with up to twenty meters high, look at the disaster site.

The material further landslide had rolled through the valley groove which is where water normally flows (flow tracks), well water sourced from springs and rainwater runoff. Flow along this valley, material loosened component flows toward the bottom while grind along the left and right side of the valley (lateral erosion), so that when she reached the foot of the slopes, avalanche of material volume seemed so much more. The material flow can take place quickly to very quickly depending on the slope of the valley groove track and the viscosity or viscosity material. Not surprisingly, the material flow avalanches often seen veering following the path of the flow of the valley. Trails valley avalanche of material flow in Kampung Dewata reached along more than eight hundred meters.

At the bottom of the valley groove track, avalanches material is generally spread in all directions. In this place ordinary people lived, so catastrophic result of this process can occur. Areas of material deposition is usually preceded their buckling slope (foot slope), which is where the change of morphology formed by a slope that slopes more gentle slope morphology. In a landslide in Kampung Bali, precipitated this material could reach more than three meters, so it would almost certainly be able to cover the houses which have been butted.

Cause

From the description of the characteristics of the type of material flow landslides loosened component, implied clearly the various factors that may cause the formation of landslides in Kampung Bali, Ciwidey.

Naturally, every slopes prone to landslide and increasingly steep slope, the higher the potential for the occurrence of landslides. Conditions were very steep slope or almost upright control the formation of avalanches start. This condition is exacerbated thick residual soil that make up the slopes. Moreover, the nature of the bedrock is relatively impermeable from residual soil, also controls the formation of landslides. Their springs at the bottom of the escarpment crown this initial avalanche has indicated an increase in pore pressure significant in the field of collapse.

Rainfall is high enough in the last few weeks can not be separated as factors trigger this landslide. While forest cover has not changed, the effective voltage drop due to the increase in pore pressure by infiltration of rainwater will contribute considerably to the process of formation of avalanches. Therefore, the land mass seemed not strong longer sustain itself, let alone the heavy mass has also been increased by the infiltration of rainwater.

An understanding of the types, characteristics, and factors that cause landslides is a fundamental aspect in the monitoring of efforts. Without this, the monitoring efforts are often less effective. Monitoring landslides loosened component type of material flow should be focused in the area of ​​the main avalanche of material resources. This area generally occupied areas with slope steep to very steep. The presence of cracks in the head long- soran to watch. These cracks sometimes invisible, but can often be recognized from the power behavior of higher water infiltration in that section. If the avalanche early-moving pretty slow to moderate or even gradually, the symptoms of other concomitant easily recognizable, among others, with the trees or poles are leaning toward the bottom of the slope, or the deflection (bulging) at the foot of the slopes which is sometimes accompanied by the appearance of zones of seepage or springs.

Through the efforts of monitoring, the potential for landslides should be known early. The question that often arises, who should do the monitoring? Nowadays, of course, every adult individuals are expected to contribute to this monitoring, especially for those who live in areas vulnerable to landslides.

mitigation

As well as monitoring, mitigation of landslides should be based on understanding of the types, characteristics, and factors that cause avalanche itself, so that mitigation is done will be more focused.

Associated with this type of landslides loosened component in the form of material flow, mitigation can be done both in the area of ​​the main avalanche of material resources, flow lines, and even in the area of ​​deposition material. In the main area avalanche of material resources, disaster mitigation is more emphasis on the prevention of the occurrence of landslides, by protecting and strengthening the slopes if necessary. Along the flow path, need to be made barrier construction material destruction rate that takes into account the estimated volume of material and the slope of the valley groove, for example by building several dams along the channel. As in the deposition area, mitigation can be done through the arrangement of settlements such that the avalanche of material will not hit residential location, or through the creation of construction material flow solver avalanche before reaching settlements.

In addition to structural mitigation can also be done nonstructural, among others, by doing socialization in order to increase understanding and awareness of the potential for landslides in the vicinity. People should know what needs to be done and avoided according to the type, characteristics, and factors that cause landslides in the vicinity.

High rainfall expected to continue through the next few months. For that, there is no harm us all put alert to the condition of the slopes around us, or will we let the next landslide happened with offhand? ***

Writer, member of the Scientific Group of Applied Geology FITB-ITB, Chairman of the Program Bachelor of Geological Engineering FITB-ITB, and Chairman of the Division of Engineering Geology-IAGI.

Source (Mind, March 1, 2010 Print Edition)

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