From geographic and geologic characteristic of the location, Indonesia is one of areas that very susceptible to flood disaster. It is especially true for the western Indonesia with greater amount of rainfall than the eastern. Accorded to its morphologic condition, the cause of flood is relief of the landscape that very extensive and many of river flows among them.
Flood is a natural phenomenon caused by incapacity of water flow system which composed of river, natural watercourse and drainage system, artificial canal for flood receptacle to accumulate rain water due to high amount of rainfall thus make water overflows and floods slope area around this system.
Water capacity mentioned above is not permanently same, but it is changed due to sedimentation, river constriction related to natural phenomenon (lava, landslide, etc) or human’s activities (build facilities without considering AMDAL, throw waste on the river or other drainage outlets, etc).
Denudation of forest in rain capture area also increase flood debit because water debit collected within this system is much greater than before thus exceeds its flow capacity and triggers erosion on steep area which finally cause sedimentation in water flow system.
The decrease of water absorption area due to change of land use was also increase flood debit. Area with dense building or homes had reduced water absorption to the ground. If there is rain with great amount of rainfall, then most of the water will become surface water that directly enter to flow system and it will cause flood when the capacity is over limit.
The impact of flood is vary on several aspects, such as social (victims, injured, lost, disease, isolated people), economic (job lost, property, disturbance of daily activity), infrastructure/physical facility (damage of building, road, bridge, electrical installation, drinking water system, telecommunication system), and environmental (ecosystem damage, pure water, field, etc).
Structural/physical handling of flood is taken by building dikes on the river, dam, canal flood, normalization of river flow, sediment digging, checking dam for sediment control, building alternative system of drainage (pipe system), and interconnection among rivers. The building of these flood controllers must be planned comprehensively, combination or interconnection of buildings for flood controller can be well implemented through a properly technical plan. Technical plan is not only based on a certain number of flood debit but also considering/anticipating a greater amount of flood debit from the number predicted.
Non-physical handling is taken through participation of the people, for example by counseling and education to people (about the harm of flood, its impact and methods for prevention, NGO in handling this disaster is expected can improve people awareness to manage littering, pruning natural plants around the river), land and water conservation in the upper course of river flow area, management of flood area (such as land structuring and engineering), law enactment in order to comply with rules related to layout and cultivation in flood area, overcoming of poverty.
Sources : Banjir, Masalah Banjir Dan Upaya Mengatasinya (Siswoko), Partisipasi Masyarakat dalam Penanggulangan Banjir (Unesco), Pedoman Penanggulangan Bencana Banjir (BAKORNAS), Program Pelatihan Manajemen Bencana (undp)
