THE TRIGGERS OF SEDIMENT - RELATED DISASTER

1. INDONESIA SITUATED BETWEEN TWO VOLCANIC BELT

The location of Indonesia archipelagos in inside circum Pacific Volcanic Mobile Belt and Trans Asiatic Volcanic Belt, thus approximately 17% volcanoes in the world spread all over Indonesia. It is recognized by three volcanic zone that can be found here; there are Alphine Mountains Zone (Sunda Mountains Zone), East Asiatic Zone (Minahasa-Sangir-Ragay), and Australian Circum Zone (Halmahera-Ternate Zone). This formation is called volcanic belt.



2. INDONESIA LOCATED IN FAUTL REGION
Some part of Indonesia are active fault areas; this certain area is very unstable because it always moves. So that in Indonesia earthquake happens very often. It shake and makes particles of soil separated or in other world, it becomes less cohesion. In this condition those particles of soil will be easily washed out by water. That is how sediment-related disaster generated.

Tectonic Plate, (Simanjuntak, 1994)

3. MOUNTAINOUS TOPOGRAPHY
As mentioned before, Indonesia is located between two volcanic belt; the consequence is most of its topography mountainous with very steep slope. In some area the inclination is more than 30 degree, where is very potential for sediment-related disaster occurred.
4. DISTANT COASTAL LINE
As an archipelago country, Indonesia has very long coastal line. The abrasion of coastal line and tsunami is the matters to be concerned because beside disaster as primary effect, it may also decrease Indonesia territory.

5. HIGH RAINFALL
Indonesia is one of countries with very high rainfall. Average cumulative rainfall is about 2,000 mm per year. Furthermore, in mountain area it is reached around 4,000 mm per year. So that Indonesia becomes one of the water richest countries in the world.
















6. GLOBAL WARMING AND CLIMATE CHANGE
Climate change has caused severe climate cycles, it is notice that the temperature of earth surface in 1970 to 1980 is relatively higher previews years but in 1980 to 1990 it became colder. The cycles still continue, at the beginning of 21st centaury the earth temperature has increased again and so the temperature of atmosphere is, the increment is about 3o C. This phenomenon is related to many complex factors, whether natural or human factors. This uncertain climate behavior may also triggers natural disaster.


7. HUMAN DOMINATION
Indonesia is one of the high populated countries in the world. As the population grows, the demand for settlement will also increase. This situation will give a great effect in environment changing, such as nature balance, human relationship to other, and relationship between human with nature it self. In other world, human plays important role on environment changing.

Meanwhile, almost all natural disaster that recently occurred is as the result of irresponsible human activities that disturb nature balance. For example erosion caused by improper method of agriculture and pollution caused by vehicles, industries, etc,.

EL Nino and La Nina are some evidences related to phenomenon of climate change. In Indonesia it is recognized by typhoon or cyclone which is more frequently happened. By local people it is called Kololilimbun or Puting Beliung. This cyclone is always followed by heavy rain, and then the water will flush away the materials that is brought by it, which is consist of sediment, trees, and woods, those materials give more damages than pure water does.




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Why Indonesia Need Sabo?

Prolog

More than three decades since the first Indonesia Sabodam was built in 1970. Through those years Sabo Technology, which was developed by Japan, has been improved and modified, both is structure and functions. In the early of its development , Sabo Technology was designed only for sediment (sand) controlling purposed in volcanic areas. Nowadays, it is also implemented in non-volcanic areas , especially in the rivers which debris mass movement ( GALADO-local name ) is frequently occurred.

Although recently Sabodam is easily found almost in all over Indonesia, many people have not understood its functions yet and why it is very important in Indonesia. “ Why Indonesia needs Sabo? “ was designed by Experimental Station for Sabo Team to explain the benefits and advantages of Sabo Technology implementation in Indonesia.

Hopefully this book will enlighten and give some useful information not only for communities but also engineers and policy executors so they will understand more about Sabo Technology. Finally, we wish that this book will contribute to enrich Indonesia literary.

SABO-TECHNO AS CLEAN TECHNOLOGY

During several last years there are some misperceptions that Sabo-techno is related to a big scale massive structure with an expensive cost, in additional some said that it is only a useless monument because its function only can be seen when debris flow occurred which is very rarely event. So the community can not experience its function directly. Furthermore by the end of 20th centaury when the environment issues become more important, Sabo-techno is accused for causing damages on river morphology and ecology-system. The fact that its function will protect the community in the downstream from debris mass movement was not realized at all. For an instance in case if there are no Sabo dams in Boyong River (BO-D6 structure) then debris mass movement from Mount Merapi lahar in 1994 will effect greater numbers of victims.

Sabo works is not always identically to civil engineering structure. Although early warning system is also one part of comprehensive Sabo works, so are hillside works such as reforestation, regreening, and grass planting on dike revetment. It is to be notice that the implementation of Sabo-Techno through vegetative approach (non-structure) is important and unsubstitude as ecological aspect. Even though it has to be realized that the approach is along term activity which is took longer time has many obstacles to be applied in the hillside than structure approach. It is the reasons why structure approach as a quick yielding action also important to be combining.

The meaning of development is to achieve a better condition in the future by doing changes on present condition. The purpose of Sabo-Techno implementation in the future is first, to protect the community and its property from debris mass movement disaster and give secure feeling to them; second, to maintain natural resources sustainable and improve the surround environment; third, to protect the productive and public infrastructure area from debris mass movement.

If the implementation of Sabo-techno could be develop and applied in a proper and wise approach then it should not be emphasized to state that Sabo-Techno is a CLEAN TECHNOLOGY.

Experimental Station for Sabo as Sabo-Techno Scientific Backbone


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THE FUTURE CHALLENGE

Generally the aim of the Sabo-Techno application is to control debris mass movement (sediment and other detritus) by REDUCING, CONTROLLING and PREVENTING its power in causing disaster and property losses, and also saving people lives. Despite that, it is not realized that at the same Sabo structure will give contribution on raising the ground water table in order to fill up the aquifer as SAND FILLED RESERVOIR.

The forestation or regreening activity also can be categorized as one of Sabo activities. The principle of natural disaster counter measures that is caused by the debris mass movement is to control the mass movement debris so that it will not cause damages or dangerous to the communities. Deforestation is one causes of debris mass movement. In the well-vegetative covering mountains area, the run-off coefficient and erosion tend to decrease so that the mass movement debris will be reduced. Therefore, Sabo-Techno is combination between the work vegetation and civil engineering. That is why it is called as synthetic technology that was appropriate applied in order to deals with the natural disaster such as debris mass movement.

The debris mass movement does not always move from upstream to downstream. The TSUNAMI disaster that happened at the end of 2004 was also debris mass movement that was very extraordinary, where the current moved from lower to the upstream by the crashing of the tidal wave. Debris and the other detritus that were carried also caused serious damage in river basin area, contaminated fresh water sources including its infrastructure, and disrupted the provisions of clean water for community. Sediment debris (sediment and other detritus) inundation on the rivers had been reduced the capacity of the river channel. This condition was very dangerous and potential caused the secondary disaster such as flood or debris mass movement. The impact of tidal wave and debris flow inundation were also damage irrigation facilities. It also destroyed ecosystem in along coastal area. It is the future challenge for the next Sabo-Techno improvement.

As the front counter of sediment-related disaster, Sabo works can be classified into three counter areas :HILLSIDE SABO WORKS in upstream area, TORRENT SABO WORK in transition area, and COASTAL SABO WORKS in downstream/coastal area. Today the implementation of the Sabo works is limited on hillside and torrent Sabo works. It is the new challenge for The Experimental Station for Sabo as research institution to expand Sabo-Techno application in disaster counter measures, especially in coastal area in order to prevent abrasion and tsunami.


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