Land Subsidence Analysis of Reclaimed Land using Time-Lapse Microgravity Anomaly in Manado, Indonesia

Abstract

Coastal area land reclamation is a policy with various benefits, including its potential to increase economic growth. However, reclamation also potentially has adverse impacts on the environment, including increasing pressure on biodiversity, natural resources and natural ecosystems, and the most common problem is land subsidence. This study uses time-lapse microgravity anomaly to ascertain the distribution of gravity and vertical gradient anomaly in order to map the subsidence characteristics occurring in the Manado reclamation area. From the research that has been previously conducted, the positive gravity anomaly is spread around Megamall-Multimart to the north of Monaco Bay and on the southern side of Manado Town Square (Mantos). Positive anomaly values range from 3 to 29.7 μGal. The negative anomaly values are scattered around the Mantos and Megamas separating bridge and at some points around the Whiz Prime Hotel, Menora Church and towards the Pohon Kasih Megamas area. The reclaimed areas generally experience subsidence accompanied by a reduction in groundwater mass (Megamall and Mantos) due to the use of the groundwater by the community in these areas. Uplifts also occur at some points in the reclamation area of Megamas as a result of the occurrence of land subsidence. Longer-term research is needed to determine whether there is an increase in the rate of land subsidence in the Manado reclamation area. Over a longer period of time it can also be established whether there are other factors which affect land subsidence. Other geodetic methods to monitor subsidence, such as levelling, InSAR and GPS survey, which have been conducted in other locations, are also needed to obtain more detailed information about the land subsidence in this area.

Comparative Study of Gradient Gravity Method Between Signal Processing and Direct Measurement

“…The main factor that influences the measurement of the vertical gradient gravity method is the free air factor because in the measurement process this method requires two measurements at one measurement point location. The first measurement is carried out above the ground or the height of the gravimeter is close to 0 cm, then at the same point the second measurement is carried out by lifting the gravimeter with a tripod at a certain height [9]. The scheme for measuring the gravity of the vertical gradient can be seen in Figure 1.…”

Analysis and Interpretation of Time-Lapse Micorgravity Data Case Study in Kota Lama Semarang Tourism Area

“…A simple Bouguer anomaly contour map in the January and June 2019 periods is shown in FIGURE 7 below. Based on theoretical studies [12], [13], the results of modeling and contour of gravity data, in general, are interesting is the intermittent microgravity anomaly, not the value of gravity for each period. In each period, we only know the value (quantity) and have no physical artist at that time.…”

Comparative Studies Of Residual Water Level In Manado And Melonguane Coastal Area During Tropical Cyclone In 2021

“…As an area located on the coast and directly bordering the Pacific Ocean, North Sulawesi is vulnerable to coastal flooding, especially in Manado City. Wibowo et al (2018) found that the Manado reclamation area experienced land subsidence and groundwater levels. This is in line with research by Triana & Janottama (2021) which projected that Manado, along with other coastal cities in Southeast Asia, will experience a higher rate of sea level rise than the global average.…”