Source: TIMES Indonesia
Date: 18 Juni 2020

The problem of flooding and tidal flooding in the Semarang-Demak coastal area is not a new problem. At least this condition has occurred around a decade ago.

However, this problem has only recently gotten worse. According to some experts, this is triggered by several factors and is very complex.

From the development carried out at the coastal region, both for the industry and the development plan of embankments and sea tolls, climate change, the distance of the Earth and the Moon at the closest distance, the problem of excessive groundwater extraction and high loading (development), which result in land subsidence.

According to Bosman Batubara, a doctoral student at IHE Delft, Institute for Water Education and the University of Amsterdam, climate change does indeed cause sea level rise, however various research data show that sea level rise in the North Coast of Java region is no more than 1 cm/year.

Even though it is true that climate change causes sea level rise and contributes to tides, but specifically for Semarang-Demak, there is another dominant causal factor, namely land subsidence.

A similar sentiment was also conveyed by Mila Karmilah, Lecturer in Regional and City Planning Semarang Unissula. She conveyed that climate change is one of the many factors that cause flooding and tidal flooding on the coast of Demak and Semarang.

While related to land subsidence data, Bosman said that there are spatial variations in land subsidence in the Semarang-Demak coastal area.

From April 2016 to October 2019, in the Southwest part, land subsidence was 0-2 cm/year. While in the Northeast to Demak, land subsidence was 13 cm/year.

"Other data that I can convey, for example, came from interviews that I conducted with Semarang City Public Works staff and accompanying field visits to the Semarang River pump house in December 2019. At the Kali River pump house, there was a gauge for land subsidence. Noted that from 5/12/2012 to 6/11/2019 there had been a decrease in the location of 68 cm. If the aggregate decrease was divided by time, then the rate of land subsidence would be almost 10 cm/year," said Bosman to Times Indonesia, Wednesday (06/17/2020). 

Bosman added that there were 4 factors that were often mentioned as causes of land subsidence, namely: groundwater extraction, the load of buildings, structures, landfills, compaction or consolidation of fresh alluvial sediments, and tectonic activity. While among policymakers and researchers, what is often debated or discussed as the cause of land subsidence in the Semarang area is groundwater extraction and building construction.

"However, in the media, there are also expert opinions that mention other causes, namely developments that jutting into the sea in the Semarang Region such as reclamation, ports and industrial zones. I call this the fifth cause. In some conversation with the people in the field, many of the confessions that I heard agreed on the fifth cause," he added.

Bosman further explained that the presence of industrial zones contributes to load addition and groundwater extraction. "As for the 2013 study (Valentino D (2013) A review of the supervision of the utilization of groundwater resources in the industrial area of the City of Semarang. Regional and Environmental Journal, 1 (3): 265-274) states that eight industrial areas studied in Semarang, all of them use groundwater. The majority of the industrial area (seven industrial areas) extract groundwater by using boreholes, and one other through dug wells," he said.

The situation amid tidal flooding in the Bedono Village, Sayung Subdistrict, Demak Regency, Thursday (18/06/2020). Fuhatur Rohman

Completing the data, Mila Karmilah added that so far there are a number of industries in the Semarang-Demak coastal region. She mentioned that there are 67 particular industries in Genuk and Terboyo.

This number does not include those in the Wijayakusuma bonded industrial zone (Tugu-West Semarang), the temple industrial estate (26 industries), the Guna Mekar Industrial Estate (Kel Aji Ngaliyan Pond) where there are 48 industries and the BSB industrial area (3 companies). In addition, there are also warehouses in the Port of Tanjung Mas, then in the area of the industrial designation area (KPI) there are 8 districts and 2 are in the coastal area, namely Sayung and Karang Tengah sub-districts.

"With so many industries, such as in Tugu, Terboyo-Genuk and harbor districts, it certainly contributes to the extraction of groundwater and development on it will only worsen the occurrence of flooding and tidal flooding," said Mila.

For this reason, Mila assessed that the government should not carry out massive development in the coastal areas. In addition, she added that the public could be invited to think of the best solution that could minimize the occurrence of flooding and tidal flooding in the region.

"Coastal communities are people who are accustomed to live with the existing conditions and certainly have solutions that can be offered to the government. Then flooding and tidal flooding is one form of disaster that needs to be included in the mitigation agenda policy. Then develop community-based Early Warning System," he said.

While responding to the Semarang-Demak Sea Levee Toll Road Project (TTLSD) which was encouraged by the government to be the solution to this problem, Bosman judged this to be counterproductive.

"TTLSD is part of the spatial concentration in the Northern area of Semarang-Demak, starting from the construction of buildings, the possibility of land reclamation, and the possibility of increasing the intensity of transportation modes. All of that means there will be an increase in the burden on areas in the Northern area of Semarang and Demak. This means that it will worsen land subsidence and this will increase the risk of tidal flooding in the region," Bosman explained.

So, according to him, what the government should have done before coming out with a technical solution such as TTLSD is to conduct a deeper analysis of the complexity of the flooding and tidal flooding that occur in the Semarang-Demak coastal area, and from there work on solutions that do not risk adding the complexity of the problem.