Preventing Rising Sea Level

Infrastructure is the main solution to curb the rising sea water level. However, infrastructure development must be followed by water resources management to reduce land subsidence.

KOMPAS/P RADITYA MAHENDRA YASA

A house that sank and was abandoned by residents in Sriwulan Village, Sayung District, Demak Regency, Central Java, Monday (2/9/2019). Abrasion, high tides and climate change are the main problems on the north coast of Central Java.

Sea level rise has become a major threat to coastal areas. The tide has become a disaster as it is getting wider inundating the land with a height that sometimes reaches 1 meter.

As a result, tidal flooding often inundates residential areas, public facilities, industries and roads in coastal areas. Tidal flooding can also inundate areas far from the coast through rivers or drainage.

This tidal flood phenomenon is worsened by land subsidence in several coastal areas. Land subsidence is normal in coastal areas as a natural compaction process in alluvial soils. However, according to Heri Andreas, a geodesy expert at the Bandung Institute of Technology (ITB), the main cause of land subsidence is groundwater exploitation. "In urban areas, this accounts for 50 percent of land subsidence," he said.

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According to research conducted by Heri, this land subsidence is more severe than the sea level rise. In Semarang, Surabaya and Jakarta, the soil surface is subsiding 15 centimeters a year. In fact, in Pekalongan, the land subsidence is up to 18 cm per year.

Physical adaptation

Tidal floods have become more frequent in several coastal areas of Indonesia. Some cities have adapted. However, many cities are not ready yet.

Based on a study by Kompas on 21 main cities on the coasts of Indonesia, 18 cities have not prepared mitigation efforts to adapt to rising sea levels. There are only three local governments, namely those of Semarang, Jakarta and Surabaya, that have made anticipatory efforts.

Among the efforts are the construction of infrastructure facilities to control tidal flood, such as sea dikes, coastal embankments, polders, mobile weirs and retention ponds. Such infrastructure facilities can prevent the water from entering the mainland.

The development of physical infrastructure is not only carried out in Indonesia, but also in other countries in the world that are facing the threat of rising sea levels. Singapore, in 2008, built the Marina Barrage, a mobile weir equipped with seven giant pumps.

Kompas/AGUS SUSANTO

Aerial photo of a fishing village fortified with embankments around the old port of Kalibaru in Cilincing District, North Jakarta, Wednesday (17/2/2021). The existence of the embankment is considered important to anticipate the rate of land subsidence on the north coast and to prevent tidal flooding

The Italian city of Venice has, since 2003, operated a movable weir system (Mose) consisting of dozens of floodgates and can be raised automatically. The Mose is designed to protect the lagoon and city from high tides of up to 3 meters and at the same time to anticipate a 60 cm rise in sea level over the next 100 years.Although physical buildings can directly block the entry of sea water into the land, the construction costs are quite expensive, especially sea or coastal embankments. As an illustration, the construction of a sea embankment in Semarang that also functions as a toll road stretching 27 kilometers from Semarang to Demak costs Rp 15 trillion (US$1.05 billion).

On the other hand, embankments or other physical infrastructure have an operational age limit which has to be reviewed every 25 or 30 years. For example, a 100-square-meter segment of the National Capital Integrated Coastal Development (NCICD) beach safety embankment, which was only completed in December 2019, has broken. The damage occurred on the east side of the Nizam Zachman Ocean Fishing Port, Muara Baru, Jakarta.

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The construction of a polder and retention pond is less costly than an embankment, but they need a large pool which requires land acquisition. In addition, if the pond is not maintained, there will be new problems such as garbage accumulation and a decline in the water quality.

Polders and retention ponds both need a pumping system to regulate the flow of water. Such a pumping system failed to work when Semarang experienced major flooding in early 2021. The sea water and the river water that entered the retention pond could not be pumped out due to damage in the pumping equipment and human negligence.

Like it or not, the solutions that have been put forward are those that must be fast and permanent.

A senior official at the Infrastructure and Environmental Research and Development Department of the Semarang Development Planning Agency, M. Luthfi Eko Nugroho, believed the construction of an embankment was the most effective way to protect coastal communities and the city\'s economy from tidal flooding. For example, a sheet-pile structure has been built in Kampung Tambaklorok, the largest fishing settlement in Semarang, to prevent seawater from entering the mainland.

According to the director of environment at the National Development Planning Agency (Bappenas), Medrilzam, with the current condition, the government did not have many choices but to build an embankment in a number of coastal areas in the country in order to curb rising sea levels as well as land subsidence. Without such a solution, the lives of the people in the area can be disrupted. “Like it or not, the solutions that have been put forward are those that must be fast and permanent. In other words, we have to provide certainty," he said.

KOMPAS/P RADITYA MAHENDRA YASA

Retention pond and pump station on the Semarang River, Semarang City, Central Java, Thursday (6/12/2018). Retention ponds and a number of pump houses play a very important role in reducing the impact of flood inundation that has begun to occur in the city of Semarang.

Apart from relying on physical infrastructure, several cities have also started to restore mangroves in their coastal areas. Makassar, Surabaya, Tanjung Pinang, Demak, Tuban, Cirebon and Pekalongan have planted mangroves to prevent tidal waves from entering the mainland.

Land subsidence

In addition to rising sea levels, the most imminent threat to coastal areas is land subsidence. However, local governments in coastal areas have not made any special efforts to deal with the problem apart from the issuance of a regulation to limit groundwater extraction and imposition of taxes.

According to Heri Andreas, water management in Indonesia has to be reformed after the embankment construction. If water exploitation continues, the embankment will also go down with the ground and lose its function.

“The dyke is a painkiller. If land subsidence can be stopped, the embankment only needs to be built once,” he said.

In some other countries, apart from physical infrastructure, a number of cities also have long-standing policies for managing water resources. Tokyo, for example, in addition to building embankments, has also limited the use of ground water for industry since 1950. Instead, clean water sources are taken from rivers, rainwater and water recycling technology. Meanwhile, Hong Kong, in addition to building embankments, has also developed an anti-flood drainage system to prevent tidal waves and run-off flooding as well as to provide alternative sources of clean water.

In addition to solutions from the government, individual adaptation is also needed in facing the threat of rising sea levels. Coastal communities must adapt to stay in the area. People in the Thousand Islands (Jakarta), Makassar, Mataram, Semarang, Surabaya, Tanjung Pinang, Bangkalan, Demak, Indramayu, Tegal and Pekalongan have to raise their houses or build temporary shelters to avoid flooding every day. However, society has limitations. Government steps are still needed, both to anticipate rising sea levels and to prevent land subsidence.

This article was translated by Hendarsyah Tarmizi.