Junun Sartohadi

Contribution of anisotropy of magnetic susceptibility (AMS) to reconstruct flooding characteristics of a 4220 BP tsunami from a thick unconsolidated structureless deposit (Banda Aceh, Sumatra)

One of the main concerns of deciphering tsunami sedimentary records along seashore is to link the emplaced layers with marine high energy events. Based on a combination of morphologic features, sedimentary figures, grain size characteristics, fossils content, microfossils assemblages, geochemical elements, heavy minerals presence; it is, in principle, possible to relate the sedimentary record to a tsunami event. However, experience shows that sometimes, in reason of a lack of any visible sedimentary features, it is hard to decide between a storm and a tsunami origin. To solve this issue, the authors have used the Anisotropy of Magnetic Susceptibility (AMS) to evidence the sediment fabric. The validity of the method for reconstructing flow direction has been proved when applied on sediments in the aftermath of a tsunami event, for which the behaviour was well documented (2004 IOT). We present herein an application of this method for a 56 cm thick paleo-deposit dated 4220 BP laying under the soil covered by the 2004 IOT, SE of Banda Aceh, North Sumatra. We analysed this homogenous deposit, lacking of any visible structure, using methods of classic sedimentology to confirm the occurrence of a high energy event. We then applied AMS technique that allowed the reconstruction of flow characteristics during sediment emplacement. We show that all the sequence was emplaced by uprush phases and that the local topography played a role on the re-orientation of a part of the uprush flow, creating strong reverse current. This particular behaviour was reported by eyewitnesses during the 2004 IOT event.

Comparing data-driven landslide susceptibility models based on participatory landslide inventory mapping in Purwosari area, Yogyakarta, Java

There are different approaches and techniques for landslide susceptibility mapping. However, no agreement has been reached in both the procedure and the use of specific controlling factors employed in the landslide susceptibility mapping. Each model has its own assumption, and the result may differ from place to place. Different landslide controlling factors and the completeness of landslide inventory may also affect the different result. Incomplete landslide inventory may produce significance error in the interpretation of the relationship between landslide and controlling factor. Comparing landslide susceptibility models using complete inventory is essential in order to identify the most realistic landslide susceptibility approach applied typically in the tropical region Indonesia. Purwosari area, Java, which has total 182 landslides occurred from 1979 to 2011, was selected as study area to evaluate three data-driven landslide susceptibility models, i.e., weight of evidence, logistic regression, and artificial neural network. Landslide in the study area is usually affected by rainfall and anthropogenic activities. The landslide typology consists of shallow translational and rotational slide. The elevation, slope, aspect, plan curvature, profile curvature, stream power index, topographic wetness index, distance to river, land use, and distance to road were selected as landslide controlling factors for the analysis. Considering the accuracy and the precision evaluations, the weight of evidence represents considerably the most realistic prediction capacities (79%) when comparing with the logistic regression (72%) and artificial neural network (71%). The linear model shows more powerful result than the nonlinear models because it fits to the area where complete landslide inventory is available, the landscape is not varied, and the occurence of landslide is evenly distributed to the class of controlling factor.

Rockfall susceptibility zoning based on back analysis of rockfall deposit inventory in Gunung Kelir, Java

A rockfall susceptibility based on trajectory-energy/velocity approach needs release area or rockfall source. However, identification of rockfall source is not always possible for some areas in Indonesia. This paper presents a rockfall susceptibility zoning based on back analysis technique of rockfall deposit inventory in Gunung Kelir, Java. There were several steps in the rockfall susceptibility zoning: (1) rockfall deposit inventory, (2) rockfall simulation based on back analysis of rockfall deposit inventory, (3) sensitivity analysis, and (4) rockfall susceptibility zoning. The result suggests that the travel distance is affected by the spatial distribution of rockfall source, lithology or surface material, and topography (angle of slope and angle of aspect). Final trajectories were employed to generate landslide susceptibility map which may allow a policy maker to have an advanced consideration to achieve specified risk measures and evaluation of their cost efficiency to optimize budget and design. Application of rockfall susceptibility zoning based on back analysis of rockfall deposits is efficient where rockfall source information is unavailable.

Dinsar technique for retrieving the volume of volcanic materials erupted by Merapi volcano

In the present paper, we propose the application of a differential synthetic aperture radar interferometry (DInSAR) technique to retrieve the volume changes of the damaged area and the volcanic sediment on the sloped surface of Merapi volcano, Indonesia, which erupted on October 26 and November 4, 2010. This technique was used to investigate the thickness of volcanic ash and the volume change of post-ejected wet lava (sand and rock) surrounding Merapi volcano by assessing L-band ALOS PALSAR data. The results reveal the volume of the damaged area, or deformation, and the volume of sedimentation in the study area are 1.4 million and 2.2 million m3, respectively, and indicate that the radius of the dangerous area is 15.6 km.

Seismic vulnerability assessment of residential buildings using logistic regression and geographic information system (GIS) in Pleret Sub District (Yogyakarta, Indonesia)

BackgroundThe Southeast of Yogyakarta City has had the heaviest damages to buildings in the 2006 of Yogyakarta Earthquake disaster. A moderate to strong earthquake of 6.3 Mw shook the 20 km southeast part of the Yogyakarta City early in the morning at 5:54 local time. On top of extensive damage in Yogyakarta and Central Java, more than 5700 people perished; 37,927 people were injured in the collapse of more than 240,396 residential buildings. Furthermore, the earthquake also affected the infrastructure and local economic activities. The total damages and losses because of the earthquake was 29.1 trillion rupiahs or equal to approximately 3.1 million US dollar. Two main factors that caused the severe damages were a dense population and the lack of seismic design of residential buildings. After reconstruction and rehabilitation, the area where the study was conducted grew into a densely populated area. This urbanistic change is feared to be potentially the lead to a great disaster if an earthquake occurs again. Thus, a comprehensive study about building vulnerability is absolutely needed in study area. Therefore, the main objective of this study has been the provision of a probabilistic model of seismic building vulnerability based on the damage data of the last big earthquake. By considering the relationship between building characteristics, site conditions, and the damage level based on probabilistic analysis, this study can offer a better understanding of earthquake damage estimation for residential building in Java.ResultsThe main findings of this study were as follows: The most vulnerable building type is the reinforced masonry structure with clay tile roof, it is located between 8.1-10 km of the epicentre and it is built on young Merapi volcanic deposits. On the contrary, the safest building type is the houses which has characteristics of reinforced masonry structure, asbestos or zinc roof type, and being located in Semilir Formation. The results showed that the building damage probability provided a high accuracy of prediction about 75.81%.ConclusionsThe results explain the prediction of building vulnerability based on the building damaged of the Yogyakarta earthquake 2006. This study is suitable for preliminary study at the region scale. Thus, the site investigation still needs to be conducted for the future research to determine the safety and vulnerability of residential building.

Ecosystem Services of Coastal Dune Systems for Hazard Mitigation: Case Studies from Vietnam, Indonesia, and Chile

In many developing and emerging tropical and subtropical countries, coastal dune systems (CDS) are under high pressure, which leads to progressive degradation and loss of dune areas. This in turn weakens the protection function against coastal hazards. In this chapter we discuss CDS in three case studies: Thua Thien-Hue province (Central Vietnam), Parangtritis (Java Island, Indonesia), and Ritoque (Central Chile). For these CDS, we assess relevant ecosystem services (ES) with particular regard to protection services as well as the current degradation status through a rapid assessment approach. Moreover, we analyse the legal frameworks for coastal dune management and protection in the case study countries. Main results include indicator sets for assessing ES and the degradation status of CDS, which are transferable to other coastal dune areas. Based on these sets we evaluate and compare the three dune systems and provide policy recommendations for a more efficient regulation and management of CDS.

Distinguishing between Hazardous Flooding and Non-Hazardous Agronomic Inundation in Irrigated Rice Fields: A Case Study from West Java

An accurate flood detection method is essential for obtaining areas of irrigated rice fields affected by flooding. This paper aims to distinguish between rice fields with flooding and rice fields with agronomic inundation using MODerate resolution Imaging Spectroradiometer (MODIS) 8 day 500 m spatial resolution (MOD09A1) imageries over irrigated rice fields with complex cropping patterns in West Java. Over the past decade, Enhanced Vegetation Index (EVI) ≤ 0.1 derived from moderate resolution remote sensing imageries has been used for detecting flooding in irrigated rice fields. Without additional farming information, this paper argues that EVI ≤ 0.1 cannot estimate flood areas correctly, given the existence of both hazardous flooding and non-hazardous agronomic inundation in irrigated rice fields. Adding a threshold of 40-day duration representing land preparation and transplanting activities enables EVI ≤ 0.1 to distinguish between agronomic inundation and flooding in irrigated rice fields. The difference in the Start of Season (SOS) between the wet planting season 2013/2014 and long-term average (2000–2015) shows that the Overall Accuracy (OA) and F1 scores are 75.96% and 81.74%, respectively. The confusion matrix using the respondents’ reports shows OA of 80.5% and Kappa of 60.16%. The quality of flood maps is partly influenced by environmental processes, human decisions, and mixed pixels.

Land use change analysis using spectral similarity and vegetation indices and its effect on runoff and sediment yield in tropical environment

Land use change influences the hydrological as well as landscape processes such as runoff and sediment yields. The main objectives of this study are to assess the land use change and its impact on the runoff and sediment yield of the upper Serayu Catchment. Land use changes of 1991 to 2014 have been analyzed. Spectral similarity and vegetation indices were used to classify the old image. Therefore, the present and the past images are comparable. The influence of the past and present land use on runoff and sediment yield has been compared with field measurement. The effect of land use changes shows the increased surface runoff which is the result of change in the curve number (CN) values. The study shows that it is possible to classify previously obtained image based on spectral characteristics and indices of major land cover types derived from recently obtained image. This avoids the necessity of having training samples which will be difficult to obtain. On the other hand, it also demonstrates that it is possible to link land cover changes with land degradation processes and finally to sedimentation in the reservoir. The only condition is the requirement for having the comparable dataset which should not be difficult to generate. Any variation inherent in the data which are other than surface reflectance has to be corrected.

The Ecological Perspective of Landslides at Soils with High Clay Content in the Middle Bogowonto Watershed, Central Java, Indonesia

The clay layers at hilly regions in the study area were very thick. The presence of very thick clay caused several difficulties in terms of environmental management, particularly in reducing georisk due to landslide. However, initial observations proved that areas of active landslides had better vegetation cover. The objective of this study was to find out ecological roles of landslides in livelihood in the Middle Bogowonto Watershed. The ecological roles of landslide were examined through field empirical evidences. Texture, bulk density, permeability, structure, and index plasticity were conducted for analyses of soil physical properties. Stepwise interpretation was made using 1 : 100,000–1 : 25,000 Indonesian topographic maps and remote sensing images of 30 m–<10 m spatial resolution. The results showed that landslides formed three landform zones: residual, erosional, and depositional zones. The area that did not slid, the residual zone, had massive soil structure and very hard consistency. Crops cultivated in this zone did not grow well. In the areas of active landslide, the environmental conditions seemed to be more favorable for living creatures. The landslides resulted in depositional zones with gentle slopes (4° to 15°), higher water availability, and easier soil management. The landslides also acted as the rearrangement process of landforms for better living environment.

Analysis of SOM and Soil Nutrients for Sustainable Agriculture in Hilly Areas: Central Part of Bogowonto Catchment, Java, Indonesia

Today, agriculture is not solely applied on plain areas but also has been expanded onto hilly areas. The understanding of SOM and soil nutrients is considered as a basis to achieve sustainable agriculture in hilly areas. The behavior of SOM and soil nutrients is very different between plain and hilly areas. The aims of this study are: (1) to analyze the specific behavior of SOM and soil nutrients in hilly areas, in order (2) to evaluate the effect of relief variation and of land uses towards those properties, and (3) to propose appropriate soil management practices in achieving sustainable agriculture in hilly areas. Field survey and laboratory analyses were conducted in this study. There were 11 soil sampling sites selected within four land use types in various relief. The results show that SOM and soil nutrients in cultivated land are lower than those in uncultivated land. There are significant differences of SOM and soil nutrient contents among the cultivated land. Mixed garden is proposed as the most appropriate land use applied in such study area, and thus it is applicable to gain the sustainable agriculture. With regards to relief variation, the intensive agricultural practices are required to be minimized, and the intercropping system is suggested for retarding the soil erosion problem.