Besides Building with Nature Demak needs to tackle subsidence to safeguard coastline

Published: 10 October 2017

Ten community leaders have signed agreements to help further restore their severely eroded coastline during a high level event organised by the Ministry of Marine Affairs and Fisheries (MMAF) of Indonesia and the public private Consortium Building with Nature (BwN) in Demak. At the same time the warning bell was sounded about the rapid subsidence in their surroundings, against which Building with Nature measures may not be able to perform.

Semarang, 10 October 2017 – At the multi-stakeholder event, the Dutch embassy in Indonesia and the Governor of Central Java handed over the so-called ‘Bio-rights’ contracts to 10 community groups in 9 villages within Demak district, Central Java. These communities have worked closely with the local government, MMAF, and the Building with Nature (BwN) Indonesia Consortium to restore mangroves and implement innovative aquaculture practices and offering alternative livelihoods that do not disturb the restored mangrove buffer.

The signing of the village contracts is an important sign of commitment by the villagers. In return for their support, which may involve giving up their fish ponds at the shoreline, the project supports them in revitalizing aquaculture ponds inland and building up new livelihoods.

“I was excited waiting for the support through the Bio-rights contract. I realise that our community must work hard and collaborate to make sustain our environment through the Building with Nature measures” conveyed pak Musthofa, the Chair of Wedung community group, one of the signatories of the contract.

Good progress

The Consortium has reported positive progress of their hybrid engineering measures constituting of permeable bamboo structures to halt erosion and allow for mangrove recovery over the past few years. Good sedimentation rates were monitored in the first year resulting from the permeable structures in front of the coast that work as a sediment trap.

Rapid soil subsidence

Today, the partners were however also warning for rapid subsidence rates and related flooding which they observe in several sites across Demak district, from Bedono up to coastal communities more to the East. After consolidation of the sediment these rates may not be enough to compensate for subsidence in the project area.

The sinking of the coastal area in Demak needs to be urgently investigated because some first observations by the BwN Consortium showed they are as high as 8 cm per year. More data has to be gathered and monitored to have all the facts at our disposal.

Bregje van Wesenbeeck, from consortium partner Deltares, said that several villagers have reported that they raise the floor of their house with 40 centimeters every three years. “With respect to our measures, we observe that mangroves settle once elevation is above mean sea level. This happened behind several structures within a year. However, this year in many areas elevation lowered again and mangroves disappeared. In addition, we see monitoring poles and structures disappear below sea level within a couple of years. Subsidence seems a lot more severe in this rural area than we initially thought”. Of course, Deltares also investigates how significant the effect of tides and weather conditions is on sediment and mangrove dynamics.

Integrated Water Resource Management plan

All partners agree that there is a shared responsibility to address subsidence problems. Groundwater abstraction is a global cause of soil subsidence in many areas of the world. Informed decisions can only be made by mapping water demands, water availability, water safety and through dialogue. It ultimately calls for an integrated water management plan.

The BwN Consortium explores the potential to shift to surface water and severely reduce ground water extractions. It is better to first map all the water demand, according to Deltares, which presented a first preliminary evaluation of water availability in Demak rivers during the event.

Femke Tonneijck, programme manager of Wetlands International: “Radical decisions need to be made about the future of this area. A paradigm shift is needed, from addressing symptoms to addressing root causes at the landscape level. We hope that Demak can be saved and we do everything that we can through Building with Nature, which we believe is the best solution for this area. But the subsidence problems need to be urgently addressed in order to protect Demak and its communities. We are seeking collaboration with all stakeholders in both city and province”.