Irwan Gumilar

Land subsidence in coastal city of Semarang (Indonesia): characteristics, impacts and causes

Semarang is the capital of Central Java province, located in the northern coast of Java island, Indonesia. Land subsidence in Semarang has been widely reported and its impacts can be seen already in daily life. Based on the estimation from Levelling, Interferometric Synthetic Aperture Radar (InSAR), Microgravity and Global Positioning System (GPS) survey methods, land subsidence with rates of up to about 19 cm/year were observed during the period of 1999 up to 2011. Results derived from GPS since 2008 up to 2011 show that land subsidence in Semarang has spatial and temporal variations, with spatial average rates of about 6 to 7 cm/year and maximum rates that can go up to 14–19 cm/year at certain locations. The northern region of Semarang along the coast exhibits higher rates of subsidence compared to its southern region, and this subsidence is believed to be caused by the combination of natural consolidation of young alluvium soil, groundwater extraction and load of buildings and constructions. The impact of land subsidence in Semarang can be seen in several forms, mainly the wider expansion of (coastal) flooding areas, cracking and damage of buildings and infrastructure, and increased inland sea water intrusion.

On the Roles of Geospatial Information for Risk Assessment of Land Subsidence in Urban Areas of Indonesia

Land subsidence is a silent hazard that may occurs in large urban areas, and usually caused by combination of excessive groundwater extraction, natural consolidation of alluvium soil, load of constructions and tectonic activities. Geospatial information is useful for studying the characteristics, causes, impacts and cost of land subsidence. This paper concentrates on the roles of geospatial information for risk assessment of land subsidence in three large cities in Indonesia, namely Jakarta, Bandung and Semarang. Geodetic based results show that land subsidence rates in all three cities generally have spatial and temporal variations, and their magnitude is in average about 5–10 cm/year and can reach up to about 20 cm/year at certain locations and times. The impact of land subsidence can be seen already in the field in forms of the buildings and infrastructure cracking, the wider expansion of (coastal) flooding areas, and increased inland sea water intrusion. Land subsidence has a strong linkage with urban development process. Urban development increases the built-up areas, population, economic and industrial activities, and also groundwater extraction, which can then lead to land subsidence.

On the establishment and implementation of GPS CORS for cadastral surveying and mapping in Indonesia

Abstract Since 2009, the latest satellite based positioning system in the form of global positioning system (GPS) continuously operating reference station (CORS) has been tested to support cadastral surveying and mapping in Indonesia, specifically in Java and Bali islands. The main aim of this GPS CORS implementation is to speed up the land registration process in Indonesia. Currently about 55% of land parcels are still to be certificated (e.g. about 48 million parcels), and about 90% of the area are still to be mapped for cadastral purposes (e.g. about 83 million ha). At present in 2013, there are 183 GPS CORS stations have been established for this purpose by the National Land Agency of Indonesia (BPN). In establishing, operating and maintaining a good and reliable GPS CORS network that can serve cadastral surveying and mapping all over Indonesia, there are several challenges and constraints that have to be properly taken into consideration mainly related to: integration of several existing GPS CORS networks in Indonesia; expanding the coverage of GPS CORS to cover a vast region of Indonesia; availability and reliability of the communication link system; establishment of reliable GPS CORS data processing and management at BPN and district land offices; spatial and temporal variations in achievable accuracy of GPS CORS derived coordinates; insufficient number of dedicated and professional GPS CORS surveyors at BPN and all district land offices; and local social and political challenges. These challenges and constraints have to be effectively overcome to have meaningful implementation of GPS CORS in supporting cadastral surveying and mapping in Indonesia. This GPS CORS network will also serve other non cadastral applications in Indonesia.

Adaptation and mitigation of land subsidence in Semarang

Land subsidence is not a new phenomenon for Semarang. Some report said the subsidence in Semarang probably is occurring for more than 100 years. Based on the leveling surveys conducted by the Centre of Environmental Geology from 1999 to 2003 it was found that relatively large subsidence was detected around Semarang Harbor, Pondok Hasanuddin, Bandar Harjo and around Semarang Tawang Railway station, with the rates ranging from 1 to 17 cm/year. Results derived from GPS show that land subsidence in Semarang has spatial and temporal variations. In general, subsidence rates in Semarang have an average rate of about 6 to 7 cm/year, with maximum rates that can go up to 14-19 cm/year at certain locations. The impact of land subsidence in Semarang can be seen in several forms, such as the wider expansion of (coastal) flooding areas “rob”, cracking of buildings and infrastructure, and increased inland sea water intrusion. It also badly influences the quality and amenity of the living environment and life (e.g. health and sanitation condition) in the affected areas. In the case of Semarang, adaptation and mitigation are considered very important. We have been done some investigations to this area by field observations (mapping the flooded area, mapping the infrastructure problems, interviewing people and seeing the adaptations, conduct GPS measurement to see deformation, etc.), gather information from Government, from digital media, etc., and we noticed people increased their house, and the local goverment elevated the road and the bridge, etc. regulary over less decade periode as part of adaptation. We also noticed the Central Goverment built the dyke and pumping station. Our conclusions said that the adaptation only made temporaly since significant land subsidence keep coming and worsening by the sea level which is keep rising. Another conclusion, so far we have seen lack of mitigation program, monitoring or even inevective mitigation in Semarang related to this subsidence issue.Land subsidence is not a new phenomenon for Semarang. Some report said the subsidence in Semarang probably is occurring for more than 100 years. Based on the leveling surveys conducted by the Centre of Environmental Geology from 1999 to 2003 it was found that relatively large subsidence was detected around Semarang Harbor, Pondok Hasanuddin, Bandar Harjo and around Semarang Tawang Railway station, with the rates ranging from 1 to 17 cm/year. Results derived from GPS show that land subsidence in Semarang has spatial and temporal variations. In general, subsidence rates in Semarang have an average rate of about 6 to 7 cm/year, with maximum rates that can go up to 14-19 cm/year at certain locations. The impact of land subsidence in Semarang can be seen in several forms, such as the wider expansion of (coastal) flooding areas “rob”, cracking of buildings and infrastructure, and increased inland sea water intrusion. It also badly influences the quality and amenity of the living environment and life (e.g. healt...

Understanding the trigger for the LUSI mud volcano eruption from ground deformation signatures

Abstract The LUSI mud volcano in the sub-district of Porong, Sidoarjo, East Java, Indonesia started to erupt on 29 May 2006. An almost continuous eruption of a mixture of mud, water and gas has occurred around this area since this date. The eruption triggered vertical and horizontal ground deformation. From June 2006 to December 2010, 14 global positioning system campaigns were conducted to observe the ground deformation using c. 50 stations sparsely located up to 10 km from the eruption centre. Field observations of cracks, terrestrial laser scanning and geo-electrical measurements have also been used to infer the ground deformation signature around the LUSI mud volcano. More than 150 pairs of interferograms generated from 66 ALOS PALSAR images from June 2006 to December 2009 have also been used to study the ground deformation caused by the LUSI mud volcano. The LUSI mud eruption began only 200 m from where the Lapindo Inc. oil company was drilling for oil and gas. The drilling may have pierced a deeper high-pressure zone, causing an underground blow-out of the drillhole into a hydrofracture. Alternatively, the magnitude 6.3 Yogyakarta earthquake, which was located c. 275 km from the eruption site and occurred two days before the LUSI eruption, may have shaken the area sufficiently to cause the eruption by reactivating a fault in the region and liquefying the mud. These two hypotheses for triggering the mud volcano have been argued vehemently and still remain controversial. The ground deformation signatures provide important clues to understanding the trigger for the eruption and to solve this controversy. Co-seismic fault reactivation has its own typical ground deformation signature. This study used global positioning system and InSAR techniques, as well as field observations of cracks, terrestrial laser scanning and geo-electrical measurements, to determine the signature of ground deformation around the LUSI mud volcano and to explain the triggering mechanism.

Land Subsidence, Groundwater Extraction, and Flooding in Bandung Basin (Indonesia)

Increase in urban development activities and urbanization rate in the Bandung Basin have increased groundwater extraction from the aquifers, which has then led to land subsidence in several locations in the basin. Based on GPS (Global Positioning System) and InSAR (Interferometry Syntetic Aperture Radar) data, the estimated subsidence rates vary spatially from 2 to 20 cm/year. Maximum subsidence during the period of 1999–2010 is about 3 m and largest in industrial areas. Site visit surveys were also conducted to map and evaluate the impacts of the land subsidence.

Landslide monitoring using terrestrial laser scanner and robotic total station in Rancabali, West Java (Indonesia)

West Java is one of the provinces in Indonesia which is prone to landslide. Over the past few years, landslides in this area have resulted in a large number of victims. One of the areas in West Java with the highest risk of landslide occurrence is Rancabali Ciwidey. In general, the morphology around the landslide location is steep hills, with the slope > 30° and the altitude between 1550 – 1865 m above sea level. Several indications of ground movements can be seen in the form of slumps and cracks on the village roads and tea plantation, as well as slanting trees and electricity poles. The ground movement monitoring in this area is necessary for disaster mitigation. Several methods that can be used to monitor the landslide are using Terrestrial Laser Scanner (TLS) and robotic total station. This research aims is monitoring the landslide using these methods. The methodology used in this research is by obtaining the scanning data using TLS C-10 and Robotic total station MS05 measurements to obtain the coordi...

On Integration of Geodetic Observation Results for Assessment of Land Subsidence Hazard Risk in Urban Areas of Indonesia

Several large urban areas in Indonesia, i.e. Jakarta, Bandung and Semarang, have experienced land subsidence. These urban land subsidences are mainly caused by the combination of excessive groundwater extraction, natural consolidation of alluvium soil, and load of constructions (i.e. settlement of high compressibility soil). The impact of land subsidence can be already seen in several forms, such as cracking of buildings and infrastructure, the wider expansion of (coastal) flooding areas, and increased inland sea water intrusion. It also badly influence the quality of living environment and life in the affected areas. Land subsidence in Jakarta has been studied using leveling surveys, GPS surveys, and InSAR techniques. The results obtained from these technique over the period between 1982 and 2011 show that observed subsidence rates in Jakarta are about 1–15 cm/year, and can reach up to 20–28 cm/year at certain location and certain period. In Bandung basin, land subsidence phenomenon has been studied using GPS surveys and InSAR methods. Based on these methods, it was found that during the period between 2000 and 2011, several locations in the Bandung basin have experienced subsidence, with an average rate of about 8 cm/year and can reach up to about 23 cm/year. In Semarang, land subsidence has been studied using Levelling surveys, GPS surveys, Microgravity surveys and InSAR technique. Based on the estimation from those measurement methods, land subsidence with rates of up to about 19 cm/year were observed during the period of 1999 up to 2011. The observed land subsidence rates in Jakarta, Bandung and Semarang in general have spatial and temporal variations. Results from various geodetic observation methods can give a better picture on the magnitudes and rates of land subsidence, and its variation both in spatial and temporal domain. Integration of those results however, can not always be performed in an ideal manner, since each geodetic method has its own operational strengths and weaknesses in large urban environment. Open image in new window Fig. 1 Large cities of Indonesia affected by land subsidence phenomena, i.e. Jakarta, Bandung and Semarang, all located in Java island

3D modelling of Mt. Talaga Bodas Crater (Indonesia) by using terrestrial laser scanner for volcano hazard mitigation

Indonesia is a country with many volcanoes. Each volcano in Indonesia typically has its own crater characteristics. One of them is the Mt.Talaga Bodas, located in Garut, West Java. Researches regarding the crater characteristics are necessary for volcanic disaster mitigation process. One of them is the modelling of the shape of the crater. One of the methods that can be used to model the volcanic crater is using Terrestrial Laser Scanner (TLS). This research aims to create a 3 dimensional (3D) model of the crater of the Mt. Talaga Bodas, that hopefully can be utilized for volcanic disaster mitigation. The methodology used in this research is by obtaining the scanning data using TLS and GPS measurements to obtain the coordinates of the reference points. The data processing methods consist of several steps, namely target to target registration, filterization, georeference, meshing point cloud, surface making, drawing, and 3D modelling. These steps were done using the Cyclone 7 software, and also using 3DS M...

Land subsidence characteristtics of Bandung Basin as revealed by ENVISAT ASAR and ALOS PALSAR interferometry

In this study, characteristics of land subsidence in Bandung Basin, Indonesia was estimated using the C-band ENVISAT ASAR and the L-band ALOS PALSAR data, acquired between 2002 to 2008 and 2007 to 2011, respectively. The software, GEOS-APSI (Advanced Persistent Scatterer Interferometry), was used to map the long term land displacement. GEOS-APSI is an in-house developed software by GEOS at UNSW for Interferometric SAR Persistent Scatterer Interferometry. Several subsidence zones were identified in the basin including areas in Cimahi, Dayeuh Kolot, Rancaekek, and Solokan Jeruk. Subsidence with a maximum of 250 mm/yr was observed in some of the zones. The results were validated with six epochs of GPS survey between 2002 and 2010. The standard deviation of difference in subsidence between InSAR and GPS measurements for ENVISAT ASAR and ALOS PALSAR was 13 mm/yr and 22 mm/yr, respectively.