Why is Semarang Sinking? Understanding the Semarang Land Subsidence Phenomenon

Semarang is a vital city in Java Island, Indonesia. This city is a major hub for trade and transportation in northern Java. Unfortunately, this region is undergoing severe land subsidence. Experts calculated that this city sinks up to 20 cm per year. Why is Semarang sinking?

Land subsidence is an environmental phenomenon in which the Earth’s surface is moving downward vertically. This occurrence may occur gradually or suddenly, depending on the triggers. Moreover, the causes of the sinking land vary from one region to another.

Why is Semarang Sinking?

Land subsidence can be caused by many factors. Some triggers are human activities, while others are natural. Due to Semarang’s condition, the city’s land subsidence is the result of man-made and natural factors.

Where is Semarang located? Semarang sits along the northern coast of Java, bordering the Java Sea. This low-lying city also sits on a thick alluvial plain. Moreover, the city is densely populated. How can those conditions affect the land level of Semarang?

1. Excessive Groundwater Extraction

Why is Semarang sinking? The major cause of land subsidence in Semarang is excessive groundwater extraction. According to research, this factor contributes up to 82% of the sinking ground level in this city.

In Semarang, an enormous volume of groundwater is pumped from wells for domestic and industrial uses. About 79% of Semarang’s water needs depend on groundwater. Moreover, most of this water is deep groundwater and the rest is shallow groundwater.

Meanwhile, citizens who don’t have groundwater wells get water from PDAM, a government-owned company that provides drinking water. PDAM water mainly comes from lakes and rivers. This company extracts and filters the water so it is drinkable.

A report said that the population in this region extracted 0.4 million cubic meters of groundwater per year in the 1900s. However, this amount increased significantly in the 2000s. Nowadays, the volume of groundwater extracted in Semarang reaches 38 million cubic meters per year.

2. Soil Compaction

Another contributor to the Semarang sinking ground is soil compaction. This region lies on a plain with young alluvial soil. This soil type is prone to compaction because it is soft, fine-grained, and undergoing natural consolidation.

Moreover, other causes, including excessive groundwater extraction, increase the rate of soil compaction in this region. Groundwater extraction will cause the soil structure to lose its support. Consequently, the ground sinks faster than its natural compaction rates.

3. Construction and Urban Development

Construction and urban development also play a vital role in the Semarang land subsidence. The load from infrastructure and urban development puts great pressure on the alluvial land in this city. Consequently, the ground is compressed, and the compaction process occurs.

The Impact of Land Subsidence in Semarang

The sinking land phenomenon has a serious impact on this city. Those who live in this region may experience the impact directly or indirectly. What are the effects of land subsidence?

• Flood: Land subsidence in a coastal region, such as Semarang, will increase tidal flood risk. This risk will be significantly higher when there is a high tide or sea-level rise. Therefore, people in Semarang will experience frequent flooding.

• Infrastructure Damage: Land sinking can damage infrastructure and residential buildings. At first, this phenomenon may only cause cracks in buildings. However, in the long term, land subsidence can lead to serious structural issues, damage bridges, broken utility pipes, and other damage.

• Disrupted Drainage System: The drainage system, including flood canals and retention ponds, cannot function as effectively as before after the land sinks. Consequently, floods will last longer. Moreover, authorities will need more equipment, such as pumps, to deal with the flood.

• Economic Losses: Floods and infrastructure damage caused by land subsidence will lead to health problems, lower property values, land losses, and expensive infrastructure repairs. Consequently, the government and communities suffer from economic losses.

• Displacement: Repeated flooding, damage, and other discomfort caused by land sinking may force people to move out of Semarang. Thus, a relocation issue may arise in the long term.

Preparing for Land Subsidence Impact

Considering the negative effects of land subsidence in Semarang, the government must work with communities to prepare for them. For example, the government must encourage people to use PDAM instead of extracting groundwater.

Moreover, the government must establish an effective flood early warning system. By using this system, authorities can warn people about flood risk, traffic congestion due to floods, etc. Therefore, they can plan some measures to stay safe.

Why is Semarang sinking? This city sinks due to groundwater extraction and other factors. The rapid land subsidence in Semarang will cause serious hazards. Thus, its government must set up an early warning system and conduct other measures to prepare for them. To aid the government in setting up the system, smsbroadcaster.com offers the best wireless alert technology.