YOGYAKARTA (KU) – Flood disaster is still threatening some areas in Indonesia, mainly in the plain areas in front of the foot of the steep hill on the river valley. To anticipate and prevent it, the geology expert of UGM, Prof. Dr. Ir. Dwikorita Karnawati, emphasized the importance of vulnerable zones mapping with appropriate and tight spatial planning for the identification and mapping of flood vulnerable zones. "By considering the natural conditions and changes in land use which are currently growing rapidly, it is estimated that flood disaster still continues to hit some vulnerable areas in Indonesia," Dwikorita told reporters on Friday (8/10).
According to Dwikorita, this vulnerable area shows distinctive characteristics of geomorphology and geology which are characterized by the appearance of fan-shaped or bird feather deposit seen from the air (satellite imagery or aerial photographs). Therefore, the zone with such condition naturally and periodically has undergone a process of concentrated flow sedimentation with a large volume of sediments.
"If we have marked these vulnerable zones, the space mapping in and around these zones should be tight to prevent accelerated sedimentation processes that form the weir on the upstream side of the river," she said.
Monitoring and early warning efforts are needed because the zones that have been identified/mapped as flood vulnerable zones should be periodically monitored in order that the occurrence of damming in upstream of river can be detected early. "This monitoring can be done through periodic visual observation every rainy season with the interpretation of satellite images or aerial photographs, or through air inspection. Monitoring needs to be tightened if the downstream area has developed into dense settlements," she said.
Monitoring can also be done by placing the early detection equipment of increased discharge of river water which is placed at some points in the upstream to downstream reions. This early detection tool can be a stretch of crossing wire perpendicular to the river valley, which, if it is broken by river flows, gives an early signal alerting the downstream river region. "The monitoring will also need to be equipped with rainfall detection devices mounted in the upstream river," she said.
The Professor of Geology and environmental engineering said that the flood and landslides are triggered by damming in the upstream, which is generally characterized by the appearance of landslide scars above the dammed river valley. Former appearance of this landslide is characterized by “claws” form (ochre "curved incisions") in the slope. "Appearance of these incisions can be easily observed from above by satellite imagery, aerial photographs or air inspection done on a helicopter/plane," she explained.
As reported, flood has struck the village of Sandur, Wasior Subdistrict, Wondama Bay Regency, West Papua, killing 89 people (predicted to continue to rise), 66 missing, 837 were injured and hundreds of houses were submerged in water or buried by rocks and soil. Several years earlier, flood disasters had also hit several regions in Indonesia, such as that at Pacet hot spring resort in Mojokerto Regency, East Java (2002). Furthermore, it also happened at Jenebarang river valley on the slopes of Mount Bawakaraeng, Goa Regency (2004); in Bahorok river bank, Bukit Lawang Tourism Park at the slope of Mount Leuser, North Sumatra (2003), in the valley/river bank in Palu; and also in Jember, East Java (2006).