**3. Land subsidence in regions of Indonesia**

Indonesia is shaped from the interaction of several major plates (e.g. Australia and Eurasia). As a consequence, Indonesia has many sediment areas. Flat sediment areas are the best places for urban and city development, especially around coastal sediment areas. Jakarta and Semarang are examples of coastal sediment cities in Indonesia. Interestingly, sediment areas are places where land subsidence generally exists. Based on our investigation of at least 17 sediment areas in Indonesia, cities, farms, fishpond areas, or peatlands, these regions are experiencing land subsidence with rates varying between 1 and 20 centimeters per year [3–5, 8, 9, 12, 14, 15] (**Figure 4** and **Table 1**).

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**Figure 4.** Places of land subsidence in Indonesian regions (sources: [3–5, 8, 9, 12, 14, 15]).

building up mangrove areas. Long-term measures include either building giant sea walls around some coastal areas or stopping land subsidence. Giant sea walls are recognized in

**Figure 3.** Example of documentation of the impact of subsidence such as cracks in buildings and infrastructures, and

Indonesia is shaped from the interaction of several major plates (e.g. Australia and Eurasia). As a consequence, Indonesia has many sediment areas. Flat sediment areas are the best places for urban and city development, especially around coastal sediment areas. Jakarta and Semarang are examples of coastal sediment cities in Indonesia. Interestingly, sediment areas are places where land subsidence generally exists. Based on our investigation of at least 17 sediment areas in Indonesia, cities, farms, fishpond areas, or peatlands, these regions are experiencing land subsidence with rates varying between 1 and 20 centimeters per year [3–5, 8, 9, 12, 14, 15]

places such as New Orleans, Tokyo, and Osaka.

42 Natural Hazards - Risk Assessment and Vulnerability Reduction

(**Figure 4** and **Table 1**).

tidal inundation (sources: [12, 13]).

**3. Land subsidence in regions of Indonesia**

Jakarta city is a well-known place for land subsidence in Indonesia. According to some publications (e.g. [3, 5, 8]) the rates of subsidence in Jakarta generally range from 1 to 10 centimeters per year and may reach 20–26 centimeters in certain places, especially in the northern part of the city (**Figure 5**). Subsidence will continue since mitigation is beyond the priority program. The linear trend of subsidence can be seen as an indicator.

Bandung is another well-known city for land subsidence in Indonesia. According to some publications (e.g. [2, 3, 8, 14]) the yearly amount of Bandung's subsidence generally ranges from 1 to 20 centimeters per year. The highest rate existed around Cimahi district in the northwestern part of the city (**Figure 5**). Generally, a linear trend can be seen, which means that subsidence may continue for quite sometime.

Semarang is also quite well known for land subsidence in Indonesia. According to some reports, subsidence in Semarang has been predicted to continue for more than 100 years. Based on some publications (e.g. [8, 9]) the yearly amount of Semarang's subsidence generally ranges from 1 to 17 centimeters per year, and in certain places, especially in the northeastern part of Semarang, it may reach 20 centimeters (**Figure 5**).

Excessive groundwater extraction in combination with natural compaction of sediments and probably tectonic deformation, land setting/reclamation, loading from the construction of new buildings, oil and gas extraction, underground mining, drainage of peatlands, etc. are considered possible causes of land subsidence in regions of Indonesia, including Jakarta, Bandung, and Semarang.

The consequences of land subsidence in Jakarta, Bandung, Semarang, and other places in Indonesia can be seen in several forms such as cracking of buildings and infrastructures,


**Figure 5.** Map of land subsidence in Jakarta, Bandung, and Semarang. Highest rate of 20 centimeters per year is represented by the red color. North Jakarta and northeastern Semarang areas are experiencing the highest rate.

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**Figure 6.** Pictures of the impact of subsidence (e.g. cracks in buildings and infrastructures and tidal inundation) in

Jakarta, Bandung, and Semarang (source: authors).

Meanwhile the highest rate in the Bandung area is in the industrial areas (modified from [5, 9, 14]).

**Table 1.** Land subsidence information in Indonesian regions.

problems with drainage, the wider expansion of flooding areas, tidal inundation, and increased inland sea water intrusion (**Figures 6** and **7**). The coastal area of Semarang city regularly suffers from tidal inundation at high tide. The same situation was happening in Jakarta before the sea dyke was established. Within this chapter we will look at the impact of land subsidence in the shape of flooding, including its wider expansion. More specifically, we will see how they are significantly correlated with each other in deriving disaster.

The consequences of land subsidence in the affected areas also badly influence the quality and amenity of the living environment, e.g., sanitation and public health. Indeed, some villagers in coastal areas have been evacuated from their homes due to permanent land sinking into the sea. The dispute as to who is responsible for these impacts is ongoing. People are spending their own money to stem these impacts, while the government is spending money on elevating roads and bridges, road repairs, and other consequences of subsidence. It is possible that there are some who contribute to subsidence along with its consequences and they should be responsible for compensating for any damage. Nevertheless, the government should have overall responsibility regarding any disaster.

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**Figure 5.** Map of land subsidence in Jakarta, Bandung, and Semarang. Highest rate of 20 centimeters per year is represented by the red color. North Jakarta and northeastern Semarang areas are experiencing the highest rate. Meanwhile the highest rate in the Bandung area is in the industrial areas (modified from [5, 9, 14]).

problems with drainage, the wider expansion of flooding areas, tidal inundation, and increased inland sea water intrusion (**Figures 6** and **7**). The coastal area of Semarang city regularly suffers from tidal inundation at high tide. The same situation was happening in Jakarta before the sea dyke was established. Within this chapter we will look at the impact of land subsidence in the shape of flooding, including its wider expansion. More specifically, we

**Notes**

6. Jakarta 1–20 Possible main causes groundwater extraction and load of building

11. Semarang 1–20 Possible main causes groundwater extraction and land reclaimed

1. Langsa Aceh 1–8 Possible main cause oil and gas extraction 2. Medan 1–8 Possible main cause groundwater extraction 3. Indragiri Hilir 1–6 Possible main cause peatland draining 4. Ogan Komering 1–6 Possible main cause peatland draining 5. Tanggerang 1–8 Possible main cause groundwater extraction

7. Bandung 1–20 Possible main cause groundwater extraction 8. Pondok Bali 1–10 Possible main cause oil and gas extraction

10. Pekalongan 1–15 Possible main cause groundwater extraction

12. Demak 1–15 Possible main cause groundwater extraction 13. Surabaya 1–5 Possible main cause groundwater extraction 14. Madura 1–6 Possible main cause oil and gas extraction 15. Denpasar 1–3 Possible main cause groundwater extraction 16. Delta Mahakam 1–3 Possible main cause oil and gas extraction 17. Kepala Burung 1–3 Possible main cause gas extraction

9. Cilacap 1–6 Possible main cause oil extraction

The consequences of land subsidence in the affected areas also badly influence the quality and amenity of the living environment, e.g., sanitation and public health. Indeed, some villagers in coastal areas have been evacuated from their homes due to permanent land sinking into the sea. The dispute as to who is responsible for these impacts is ongoing. People are spending their own money to stem these impacts, while the government is spending money on elevating roads and bridges, road repairs, and other consequences of subsidence. It is possible that there are some who contribute to subsidence along with its consequences and they should be responsible for compensating for any damage. Nevertheless, the government should have

will see how they are significantly correlated with each other in deriving disaster.

overall responsibility regarding any disaster.

**Table 1.** Land subsidence information in Indonesian regions.

**Regions Rate subsidence (cm/ year)**

44 Natural Hazards - Risk Assessment and Vulnerability Reduction

(Sources: [3–5, 8, 9, 12, 14, 15]).

**Figure 6.** Pictures of the impact of subsidence (e.g. cracks in buildings and infrastructures and tidal inundation) in Jakarta, Bandung, and Semarang (source: authors).

Comprehensively collecting information on the characteristics of land subsidence (e.g. rate, magnitude, places, causes, and impacts) in regions of Indonesia or elsewhere is appropriate for short- and long-term adaptation and mitigation (**Figure 8**). Respectively for Indonesia, short-term mitigation has been created against disasters that result in building temporary dykes, elevating the land, roads, housing, etc., including building up mangrove areas in many places along the subsiding coastal area. Long-term mitigation includes building giant sea walls around some coastal areas in an effort to stop subsidence by artificial recharge and/or

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As mentioned earlier we will look at the impact of land subsidence in the shape of flooding in some regions of Indonesia. More specifically, we will see how these are significantly correlated with each other and what the consequences of disaster would be. Fortunately, we can see quite clearly the qualitative and quantitative expected correlation between land subsidence and flooding using databases. Below is a detailed explanation of what is happening in Jakarta, Bandung, Semarang, Demak, and Pondok Bali Blanakan, which can best highlight the correlation examples. We will see clearly that the correlation is producing many problems. Where a lowland area is experiencing land subsidence as a result of a cone of subsidence or there is a subsidence bowl, water will directly flow into it and create a flood zone. If the subsidence continues over time, in this case the cone of subsidence would become larger. As a consequence, wider expansion of flooding will likely occur as well. From all parameters that may create a flood (rain intensity, retention capacity, run-off, infiltration, land subsidence, land use, etc.), the subsidence parameter will likely influence a deeper and

When we speak of a disaster from subsidence and flooding, we are likely to face economic and other losses. Millions of dollars have to be spent fixing problems from both land subsidence and flooding, and millions more will be spent in the future [17] (**Table 2**). With these kinds of losses, therefore, mitigation and/or adaptation are necessary. One key point regarding better mitigation and/or adaptation is to understand insight correlation between land subsidence and flooding. If flooding is proven to be influenced significantly by land subsidence, in this

Geologically speaking, Jakarta is a lowland flood basin area. Thirteen rivers run across the area. Therefore, Jakarta is prone to frequent flooding. When a river is beyond its capacity to retain water from heavy rainfall, then flooding will occur. On the other hand, many places in Jakarta and the surrounding area experience land subsidence. With this situation, Jakarta is even more prone to frequent flooding. Spatially, the correlation between subsidence area and flood-prone area is very clear in Jakarta. Places that are experiencing high rates of subsidence are coincidentally those places most prone to flooding, such as Pluit, Sunter, Kamal Muara, and Joglo (**Figure 9**). In Pluit and Sunter, based on people's experience, floods seem to be

case reducing or even stopping the subsidence might be the best mitigation.

stopping groundwater extraction.

wider flood over time.

**4. Land subsidence and flooding insight correlation**

**Figure 7.** Pictures of the impact of subsidence (e.g. cracks in buildings and infrastructures and tidal inundation) in other regions of Indonesia (source: authors).

**Figure 8.** Short- and long-term mitigation and adaptation against the consequences of land subsidence (e.g. elevating roads and housing, and building dykes, mangrove areas, and giant sea walls) (sources: authors, [12, 16]).

Comprehensively collecting information on the characteristics of land subsidence (e.g. rate, magnitude, places, causes, and impacts) in regions of Indonesia or elsewhere is appropriate for short- and long-term adaptation and mitigation (**Figure 8**). Respectively for Indonesia, short-term mitigation has been created against disasters that result in building temporary dykes, elevating the land, roads, housing, etc., including building up mangrove areas in many places along the subsiding coastal area. Long-term mitigation includes building giant sea walls around some coastal areas in an effort to stop subsidence by artificial recharge and/or stopping groundwater extraction.
