A sustainable solution for massive coastal erosion in Central Java - Towards Regional Scale Application of Hybrid Engineering
Deltaic populations in western Indonesia are increasingly threatened by rapid shoreline degradation and erosion. In just a few decades, some coastal areas have retreated by more than two kilometres1. Housing, roads and valuable land is literally swept into the sea. This loss of land continues unabated, sometimes by tens of metres per year. The erosion causes saline intrusion, affecting drinking water sources and agricultural production. Erosion along with soil subsidence has also led to massive flooding during storm surge, high tides or periods of excessive rainfall. Fish stocks, timber and fuelwood reserves and other valuable natural resources have collapsed. Meanwhile projected climate change aggravates vulnerability: sea-level rise and increased frequency of extreme events have introduced new challenges to which no adequate coping capacity exists. This increasingly threatens the well-being and self-reliance of millions of poor coastal communities, many of whom live below the poverty line. They are gradually losing the land and natural resource-base on which they depend.
In Demak, central Java, for example local fish pond farmers experienced a decrease in income of 60-80% following erosion of 80 km² of land, while fishermen saw their income decrease by 25- 50%2 (seeFigure 1). No less than 3000 villages on Java suffer from similar problems3.Hard-won development gains are wiped out by coastal degradation. Conflicts around remaining land and resources intensify. As a consequence, an estimated 80 million coastal inhabitants struggle to escape from an intensifying poverty cycle on Java alone4. Impacts are also experienced at macroeconomic level. The agriculture, aquaculture and fisheries sectors have experienced multi-billion losses and find it increasingly difficult to sustain their operations. These vulnerabilities will further exacerbate if the growing degradation and erosion problems are not addressed.
The ill-informed expansion of the aquaculture sector has been a prominent driver of this vulnerability. Since the 1980s, establishment of aquaculture ponds along low-lying sedimentary reaches resulted in the near total destruction of mangrove forests. No less than 750,000 ha of forest were converted, mostly in western Indonesia5. The aquaculture systems offered windfall profits initially, often to rich „patrons‟ from major cities. Following outbreak of diseases and accumulation of pesticide residues however, most systems collapsed leaving unproductive wastelands to the local population6. The removal of the mangroves and confinement of the intertidal range due to construction of earth bunds around the shrimp ponds caused changes in sediment dynamics. This triggered massive erosion and the related land loss, inundation and salt water intrusion problems.
Major investments have been made in traditional infrastructural responses – dams, sea-dykes and groins – in an attempt to resolve these problems. In most cases these failed to provide the desired protection and did not result in sufficient improvements in human welfare and economy (Figure 2). Often hard-infrastructure solutions aggravate erosion problems and subsidence due to unanticipated interferences with sediment flows and soil conditions7. Moreover, they do not revive the mangrove values that were lost. Mangrove belt establishment has been widely promoted as an alternative means to enhance coastal resilience. However, mangroves can only be successfully restored if the regional shoreline morphology (sediment flows, bathymetry etc.) and connection of the system to the river is to some degree rehabilitated as well. Most rehabilitation pilots do not reinstate these abiotic conditions. As a consequence they fail to stabilise eroding coastlines. Along many stretches of coast there is no response at all: they continue to degrade at an alarming rate.
We developed a new approach called ‘Hybrid Engineering’, which addresses delta and coastal vulnerability in an integrated manner. This approach accommodates economic and livelihood development needs, and combines technical and ecosystem-based solutions. The Hybrid Engineeringapproach is aimed to work with nature rather than against it. It combines engineering knowledge and techniques with natural processes and resources, resulting in dynamic solutions that are better able to adapt to changing circumstances. The focus of this report is on the technical solution at regional scale, i.e. a coastal stretch of 10 – 20 km long, building on experience gained with small scale pilots. The ultimate objective of this regional-scale Hybrid Engineering application is to regain coastal protection against erosion and other ecosystem services by re-establishing a mangrove green-belt. A more short-term objective of this regional-scale Hybrid Engineering application is to test and evaluate various methods of Hybrid Engineering.For the approach to succeed the development of socio-economic and governance solutions is equally important – these are however beyond the scope of the present report. In addition,we limit ourselves to coastlines, excluding mangrove rehabilitation along rivers.