Abdul Halim Hamdany

The Citarum Watershed is indeed a critical water resource in Indonesia, playing a significant role in providing water to Jakarta and other areas in West Java. However, it faces severe environmental stress due to land use changes and climate changes. The Upper Citarum Watershed, considered to be a conservation area, has experienced rapid development due to human activities and economic growth. Climate change not only affects the rainfall value but also the rainfall patterns and sediment flow. The sedimentation process significantly impacts the soil characteristics around the river body. Several factors such as topography, flow velocity, and soil texture influence the sediment characteristics. Given the critical condition of climate and land use change, this study aims to analyse the impacts of the hydrological response of land use and climate change on the sediment rate in the Upper Citarum Watershed. The land use change analysis was conducted by comparing the land use data in 2000, 2010, and 2023 in the Upper Citarum Watershed. The deposition process of solid particles such as sand, silt, and gravel that are transported in the Upper Citarum River were examined in a soil investigation. The sediment rate and deposition by river flow were analysed using HEC-RAS quasi-unsteady flow. The impact of climate change in this study was assessed by simulating the discharge in three conditions, with the first simulation using the discharge from 2000 to 2010, the second simulation using the discharge from 2011 to 2023, and the last simulation using the discharge from 2000 to 2023. Due to the land use change, the developed area increased from 4% to 24% between 2000 until 2023. The magnitude of low flow during the simulation step for three discharge gauges (Majalaya, Dayeuhkolot, and Nanjung) decreased up to 48%, but, on other hand, the sediment rate increased by 20% in Dayeuhkolot.

The interaction between moisture content and soil suction is commonly represented by a soil–water characteristic curve (SWCC). The direct measurement of water content can be easily achieved, but it usually requires a destructive method where the soil sample needs to be oven-dried. Hence, indirect measurement is commonly employed for monitoring purposes. The limitation of this approach is the variability in water content at the wilting point, particularly for plants in different types of soil. While the moisture content at the wilting point varies greatly, suction at the wilting point is typically around 1500 kPa despite varying slightly depending on the type of plant. However, suction measurement using a normal tensiometer is limited to 100 kPa due to cavitation. Hence, it is not sufficient to cover up to the wilting point. The focus of this paper is the establishment of a polymer-based tensiometer utilizing a 15 bar ceramic disc for the measurement of high suction. The suitability of the polymer-based tensiometer in measuring the soil suction of vegetative soil is conducted by performing a soil–water characteristic curve test on vegetative soil. The SWCC produced from the polymer-based tensiometer is verified using SWCC produced from a centrifuge test. The results show that the SWCCs from both polymer-based tensiometer and centrifuge tests are comparable. Hence, suction measurement using a polymer-based tensiometer is deemed reliable. This advancement in suction measurement technology is crucial for improving irrigation practices, optimizing water use, and enhancing agricultural productivity, which in turn contributes to environmental sustainability by minimizing water waste and ensuring efficient soil management.

Abstrak Perubahan iklim yang tak menentu membuat infiltrasi curah hujan dengan intensitas tinggi dapat terjadi di masa yang akan datang. Hal ini dapat menyebabkan keruntuhan pada lereng akibat infiltrasi curah hujan. Wilayah Indonesia memiliki wilayah yang sangat rentan terhadap keruntuhan lereng akibat curah hujan. Tujuan dari penelitian ini adalah untuk mengetahui karakteristik distribusi tekanan air pori dan stabilitas lereng selama hujan pada lereng asli melalui permodelan numerik. Kurva karakteristik air-tanah diukur menggunakan high-suction polymer sensors (HSPS). Perubahan volume pada tanah didapatkan menggunakan 3D scanner. Pemodelan numerik dilakukan dengan bantuan GeoStudio. Analisis rembesan dilakukan menggunakan SEEP/W untuk memperoleh perubahan distribusi tekanan air pori akibat infiltrasi curah hujan. Stabilitas lereng dilakukan dengan menggunakan SLOPE/W untuk menentukan faktor keamanan lereng akibat infiltrasi air hujan. Hasil penelitian menunjukkan intensitas dan durasi curah hujan memiliki pengaruh yang signifikan terhadap stabilitas lereng. Semakin lama durasi curah hujan dan dengan intensitas yang tinggi dapat menyebabkan penurunan faktor keamanan yang semakin besar. Hal tersebut disebabkan karena daya hisap pada tanah telah berkurang dan menyebabkan kekuatan geser pada tanah menjadi lebih rendah sehingga dapat menyebabkan kegagalan pada lereng. Kata-kata Kunci: Tanah tak jenuh, kurva karakteristik air-tanah, infiltrasi curah hujan, stabilitas lereng

This paper studies the photocatalytic performance of graphene-based titanium dioxide (TiO₂) on cementitious composites for the decomposition of Escherichia coli (E. coli) under visible light. Graphene-based TiO₂ was first synthesized through a hydrothermal process. The composites were then evaluated in terms of adsorption capability and degradation of methylene blue dyes. The adsorption test shows a remarkable increase in the amount of dye adsorbed into the composite surface. GO-P25 could adsorb around 60% of the initial dye, while less than 10% of the initial dye was adsorbed by pristine TiO₂-P25. The synthesized graphene-based TiO₂ significantly enhanced the dye degradation activity (94%) compared to pristine P25 (36%) and Krono (52%), even with the longer irradiation time for P25 and Krono. This led to an increase in reaction rate that was almost 20 times that of P25. Considering the good adsorption capabilities and high photodegradation of dye under visible light for GO-P25, cement-based surfaces containing GO-P25 are expected to be improved for the decomposition of Escherichia coli (E. coli) under visible light. Graphene-based TiO₂ on a cement-based surface showed high antibacterial activity with a 77% reduction in number of bacteria compared to a cement-based surface containing pristine TiO₂. This study confirms the effectiveness of the composites for disinfection of E. coli under visible light.

Soil suction plays an important role in governing the stability of slopes. Environmental sustainability could be jeopardized by hazards, such as slope failures (forest destruction, landscape alteration, etc.). However, the quantification of the suction effect on slope stability is a challenging task as the soil suction is usually affected by the precipitation and evapotranspiration. Numerical simulation plays an important role in the estimation of contour in soil suction due to rainfall and evapotranspiration as long-term and widespread monitoring is rarely conducted. The result of numerical simulation is highly dependent on the accuracy of the input parameters. Hence, suction monitoring plays an important role in verifying the result of numerical simulation. However, as a conventional tensiometer is limited to 100 kPa soil suction, it is hard to verify the performance of numerical simulation where suction is higher than 100 kPa. The osmotic tensiometer developed by Nanyang Technological University (NTU) can overcome this problem. It is now possible to monitor changes in soil suction higher than 100 kPa (up to 2500 kPa) for an extended period in the field. In this study, a procedure was proposed to estimate suction changes in residual soil based on rainfall and evapotranspiration data. Numerical simulation was carried out based on the soil properties and geometry of a residual soil slope from Jurong Formation Singapore. Changes in soil suction due to rainfall and evaporation were simulated and compared with the readings from the NTU osmotic tensiometers installed at 0.15 m and 0.50 m from the slope surface in the field. It was observed that numerical simulation was able to capture the variations of suctions accurately at greater depths. However, at shallow depths, erratic suction changes due to difficulties in capturing transpiration.

Ignoring the role of soil suction and implementing unsaturated soil mechanics when assessing slope stability in Indonesia is a common practice. One of the main reasons is due to the precognition that incorporating soil suction means using higher shear strength, which leads to less conservative analysis, while it is difficult to practically obtain accurate input parameters for unsaturated soil analysis. However, a number of slope failures occur all over the world due to rainfall, which becomes evidence that ignoring the role of soil suction may not necessarily lead to a conservative result. On 9 January 2021, rainfall-induced slope failure occurred at Cimanggung after four hours of heavy rainfall and killed 32 people. Many of them were injured, and houses were destroyed. This event shows the significance of considering the interaction between infiltration and soil suction when conducting slope stability analysis. Difficulties in obtaining input parameters for unsaturated soil analysis experimentally hindered practitioners in applying unsaturated soil mechanics. While the parameters can be estimated, it is always of question whether the estimated parameters are sufficiently accurate for practical purposes. In this paper, conventional site investigations were carried out while unsaturated soil parameters were estimated to study the mechanism which triggers the landslide that occurred at Cimanggung. It will be shown that estimating unsaturated soil parameters can be practically accurate and manage to capture the failure mechanism such as critical rainfall duration and critical slip surface.

Graphene oxide-titanium dioxide (GO-TiO₂) composite was synthesized with one step hydrothermal process. The structure and morphology were characterized by field-emission-scanning-electron-microscopy, Thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Photocatalytic activity against Escherichia coli inactivation was carried out by GO-TiO₂ mixed with cement composite under visible light. The result revealed no significant difference between morphology of GO-TiO₂ and pristine TiO₂. FESEM and FTIR results showed the presence of carbon component in the GO-TiO₂ composites. TGA-IR confirmed that the GO content (3%) in the composite could be controlled during the synthesis process. The synthesized GO-TiO₂ had stronger visible light absorption and narrower bandgap (3.11 eV) than TiO₂ (3.21 eV). The bandgap reduction was also observed in cement sample with GO-TiO₂ (3.08 eV) which could be beneficial for reducing the energy needed for photoexcitation. As a result, the specimen with GO-P25 outperformed specimens with others for Escherichia coli inactivation.

Photoinduced processes governed by light activated TiO₂ have been studied in many ways. One of the most active areas is the development of TiO₂ photocatalysis technologies on their application for reducing environmental impacts. The immobilization of TiO₂ on solid support, such as cementitious materials, greatly enhances its use in practical applications. In this review, a wide range of applications for achieving eco-efficient building using cementitious composite materials containing TiO₂ photocatalyst was presented. The basic mechanism of photocatalysis, such as electron excitation, charge transfer process, reactive oxygen species (ROS) generation, and its role to oxidize the pollutant and microorganisms were extensively discussed. Unlike self-cleaning and air purification systems, the study on the antibacterial function of a cement-based surface containing TiO₂ is very limited. In photocatalytic cementitious materials, the key element affecting the photocatalytic performance is the accessible active surface area. However, microstructure of cementitious materials changes with age due to hydration and surface carbonation. Hence, surface area reduction and mass transfer limitation become the main drawbacks of incorporating TiO₂ in cementitious materials. This review, therefore, provides the state of the art in photocatalytic cement-based composite materials and identifies the areas in which future improvement is needed.