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Boskalis jaarverslagen 2012

Case: Building with Nature in Indonesia

More than six thousand villages (thirty million people) on Indonesia’s enormous coastline could be washed away. Hard defenses in the form of dikes are pointless on muddy coasts like Indonesia’s. The Ecoshape consortium has engaged in a pilot project as part of the Building with Nature program in the coastal area of northern Java. The innovative approach, with dams, land reclamation and new mangrove forests, aims to turn the tide.

Men and women are up to their waists in the waters of the Java Sea. With the patience of saints, the inhabitants of the village of Timbul Sloko drag bundles of pruned branches to the location. Using sledgehammers, they have rammed poles of galam, a rapid-growing Asian wood variety, a meter and a half into the soft seabed and now they are tying in the bundles of wood using steel wire. Four dams, each one hundred meters long, are being built here. The idea is that they will help to prevent the recurring floods affecting the houses of thousands of people in the northern coastal area of Java in the district of Demak (Central Java). 

Wetlands international joins the Ecoshape consortium

Wetlands International is a international environmental organization with branches in numerous countries. In recent years, Wetlands International has already teamed up with Ecoshape on a number of pilot projects. Jane Madgwick, the CEO of Wetlands International: ‘Our objective is to bring about the restoration of wetlands in combination with improvements to the welfare of the local residents. We are seeing how wetlands are still under severe pressure throughout the world. Climate change is a new challenge, but so are the responses of governments to that challenge. At the moment, they are mainly opting for hard infrastructure. That approach is often bad for nature and, in addition, it often fails to address the water challenges adequately, particularly in the long term. The integrated solutions that Building with Nature makes possible are not only potentially more sustainable but also more attractive, cheaper and safer.’

In addition to Wetlands International the Ecoshape partners include among others Arcadis, Alterra, Haskoning, Imares and Deltares. For more information, see

Dams and mangrove 

The coast of Java is being eroded at the alarming rate of one hundred meters a year. ‘We conducted a pilot project that demonstrated that the tides deposit muddy sediment behind the dams’, says Pieter van Eijk, climate adaptation coordinator with Wetlands International. He is working on the upscaling of the dams on a stretch of coast measuring twenty kilometers. ‘In time, new mangrove forests will grow again between the dams and the coast, protecting the coast from the strong waves.’ ‘The traditional approach to land reclamation used in the past in the Netherlands has proven useful here’, explains Professor Han Winterwerp of Delft University of Technology and the research institute Deltares. A small trial dam off the coast of Java has already captured a layer of fifty centimeters of mud. ‘The first pioneering mangrove varieties are starting to grow and then the ongoing development of the forest can begin’, explains the professor.

Diseased prawns

Mangrove forests are wet, swampy forests that have, for centuries, naturally absorbed wave energy and captured sludge on the Indonesian coast. The sediment raises the level of the land, which is therefore lifted in line with the sea-level rise. The forests are breeding grounds for numerous species of fish. They clean the water and they are a source of timber. In the past, these forests have been chopped down to make way for local businesses like prawn farms. ‘As a result, the natural coastal defenses are undermined and the land has subsided, leading to flooding’, says Pieter van Eijk. ‘Another sad aspect is that the intensive use of the prawn farms meant that they were useless after only five years as the prawns became diseased. The Indonesian investors moved on to another area.’

Land reclamation

Erosion cannot be entirely prevented using dams and new mangrove forests. Random planting of mangroves will be fairly unsuccessful if the currents and waves are not absorbed and sediment isn’t captured. It is possible to help nature along by using dredging equipment to bring in mud to the coast from the shallow Java Sea close by. ‘The coastline can recover considerably within five years in this way’, thinks Jaap van Thiel de Vries, a program manager with Ecoshape and a Boskalis senior engineer.

Village elders and aquaculture

He has just returned from the area, where he sat down at the table with village elders and local governors. ‘As well as support from national and regional governments, the cooperation of local residents is indispensable’, Jaap emphasizes. In the past, this was a prosperous district but the prawn farms signaled the end for fishing and rice growing; since the collapse of prawn farming, the economy has collapsed. That is why the program also provides for new socio-economic development. ‘Drawing on expertise from Imares-Wageningen University and Research Centre, we will be developing sustainable forms of aquaculture in the abandoned ponds, as well as the sustainable use of mangroves. Even though the dams are not particularly expensive, it is still important for the economy in the hinterland to be able to finance maintenance and possible upscaling in the future.’

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