Bambang Darmo Yuwono

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...

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

Geodetic deformation monitoring at Pendidikan Diponegoro Dam

Deformation monitoring is one indicator to assess the feasibility of Dam. In order to get the correct result of the deformation, it is necessary to determine appropriate deformation monitoring network and the observation data should be analyse and evaluated carefully. Measurement and analysis of deformation requires relatively accurate data and the precision is high enough, one of the observation method that used is GPS (Global Positioning System). The research was conducted at Pendidikan Undip Dams is Dam which is located in Tembang. Diponegoro Dam was built in 2013 and a volume of 50.86 m3 of water, inundation normal width of up to 13,500 m2. The main purpose of these building is not only for drainage but also for education and micro hydro power plant etc. The main goal of this reasearch was to monitor and analyze the deformation at Pendidikan Undip Dam and to determaine whether GPS measurement could meet accuracy requirement for dam deformation measurements. Measurements were made 2 times over 2 years,...

Study of interseismic coupling rate of 2007 Mentawai earthquake using GNSS data

A maximum of horizontal interseismic velocity rate of SuGAr station is 0.4308 m/year at BTET Station (Siberut Island) and 0.0116 m/year at BSAT Station (Pagai Island) for the vertical component from GNSS data observation. Using the inversion calculation, this research calculated interseismic coupling rate of 2007 Bengkulu/Mentawai earthquake. The inversion calculation was conducted in 30×10 discrete units of earthquake plane by giving a weight of smoothing constraint and a weight of slip value constraint = 0 at the edge of the earthquake rupture area. The maximum coupling rate is located around BSAT/PRKB station (Pagai Island) and BTET/MSAI station (Siberut Island). The rupture of earthquake plane was located around BSAT/PRKB station (Pagai Island). While the earthquake plane around BTET/MSAI station (Siberut Island) has not rupture yet until now.

Preliminary survey and performance of land subsidence in North Semarang Demak

Land subsidence in Semarang is a severe hazard threatening people and urban infrastructure. Land subsidence is suspected expand to North Demak. It shows that has been leading to severe and costly damages to urban infrastructure such as buildings and roads. Another disaster like flooding will ruin the city frequently and is increasingly severely affecting the living conditions. The Principle of land subsidence monitoring with a GPS is to determine the coordinates of a point on a carefully selected location and are conducted periodically at regular. By studying the characteristic and speed of change in ellipsoid height of the point - the point of the survey is a survey to the next, then the greater the reduction in soil characteristics and will be known. This paper mainly discusses the results obtained by GPS surveys that have been conducted in 2011, 2013, 2014 and2015. Land subsidence in Semarang until now still occur, especially in the northern region of Semarang. In the range of 2011-2015 land subsidence...