Coastal Flood Management in Semarang: An Introduction to Tidal Flood Mitigation

Semarang is a low-lying city located on the northern coast of Java. This geographic condition makes this city vulnerable to coastal floods. Lately, the risk of this flood has also increased due to various actors. Consequently, the local government must have excellent coastal flood management in Semarang.

The coastal inundation management is a vital part of coastal flood mitigation. By establishing an excellent disaster risk management system, the government can minimize the coastal flood risks in Semarang and reduce casualties, fatalities, and financial losses.

About the Coastal Flooding in Semarang

Coastal/tidal floods are an annual hydrologic hazard in Semarang and other low-lying regions along the northern coast of Java. How harmful is this hazard? And what are the causes for this flood?

1. The Overview of Coastal Flood in Semarang

The Java Sea experiences high tide twice a year, i.e., from December to January and April to May. Decades ago, Java Sea’s high tide did not cause coastal flooding in northern Java. However, nowadays, this phenomenon triggers annual flooding.

In 1997, the coastal flood in this city made national headlines. This flood becomes more severe and frequent since that year. In 2022, this hydrologic hazard submerged the city at 2 m. 

The 2022 coastal flood affected thousands of people, caused economic losses, and disrupted Tanjung Mas Semarang Harbor. Meanwhile, in 2025, a combination of river and tidal floods submerged many subdistricts in Semarang for over a week.

The latest flood submerged the city by 80 cm. Moreover, it affected 40,000 people, killed 2 people, and caused over 130 people to be displaced. This hazard also badly affected a major transportation route, causing financial losses to business owners and truck drivers.

2. The Causes of Semarang Coastal Floods

The risk of tidal flood in this city increases during the rainy season, high tide, and the perigee phenomenon. However, those three factors won’t produce a serious issue without the following causes.

• Rising Sea Level: Climate change and global warming trigger the eustatic sea level rise. Experts predicted that the sea level would increase 3.2 mm/year in the Java Sea. This condition can lead to impactful and frequent coastal inundation on low-lying coasts.

• Land Subsidence: Semarang experiences severe land subsidence due to high population, urban development, and excessive groundwater extraction. The rate of land subsidence in this city reaches 9 cm/year. This condition is the major cause of tidal floods in Semarang.

• Damaged Coastal Environment: Serious damage occurred in coastal areas in Semarang due to industrialization and port development. Thus, this coastal city does not have mangrove forests to protect it from erosion and high tides.

• Inadequate Drainage: The drainage system in Semarang cannot work effectively because of several factors, including sedimentation and land subsidence. These factors cause the system to have difficulties in draining floodwater into the sea.

Coastal Flood Management in Semarang

Tidal floods in Semarang are not a new thing. The Dutch already recognized a potential problem from this hydrologic phenomenon during the Colonial Era. Therefore, the Dutch East Indies government established the Semarang coastal flood management to minimize the disaster risk. 

Nowadays, the local government of Central Java and the Indonesian government work together to manage the flood. What have those three governments done to manage the Semarang tidal flood?

1. Constructing Flood Canals

Constructing flood canals is part of the coastal flood management in Semarang. The Dutch East Indies constructed West Flood Canals from the late 1800s to the early 1900s to control tidal waves. This construction is about 9 km long.

Moreover, it functions as a major drainage channel for the western Semarang. It collects water from rivers in this city and directs its flow to the Java Sea.

On the other hand, the Indonesian government constructed the East Food Canal from 2002 to 2010. Its function is almost similar to the West Flood Canal. However, it operates in the eastern Semarang. Moreover, the East Flood Canal is about 5 km longer than the West.

2. Constructing a Sea Wall

The Indonesian government is currently constructing a giant sea wall along the Semarang coastal area and other low-lying coasts in Northern Java. The goal of this infrastructure is to prevent the seawater from flooding the inland areas that experience extreme land subsidence.

The construction of the 700-km sea wall is expected to finish within 20 years. Moreover, experts predicted that this infrastructure will cost the country 80 billion USD.

3. Constructing Retention Ponds

Retention ponds are also a part of the coastal flood management in Semarang. Currently, there is a functioning retention pond in this region, and another one is under construction. The goal of constructing these ponds is to control floodwater caused by river overflow and tidal flood.

4. Restoring Mangrove Forests

A mangrove forest restoration project is ongoing in Semarang. This project is aimed at preventing coastal erosion and mitigating tidal floods. Many parties are involved in this project. They are the government, NGOs, local communities, universities, and private companies.

The coastal flood management in Semarang includes excellent projects to mitigate tidal floods. However, the government must not forget to improve community preparedness for this hazard. The government can improve it by adopting a wireless flood warning system. Establishing this system is easy if the government has cell broadcast technology from smsbroadcaster.com.