Engineering Headway Vol. 23

Abstract: It is important to make innovations to design a breakwater model that also functions as a wave energy catcher, a space that creates resonance based on wave characteristics that produce more massive airflow. It is necessary to estimate the maximum wave runup on the OWC breakwater structure to see the runoff that occurs with certain wave conditions and water levels. The efficiency of the OWC breakwater shape and the performance of the OWC breakwater as a wave energy converter are important. In this study to determine the characteristics of waves with various variations of wave period at water depth, which will determine the steepness of the wave (H/L) which is influenced by the wave period (T). Laboratory experimental research method using a wave flume with generated wave characteristics consisting of 5 variations of period (T) i.e. 1.1 seconds, 1.2 seconds, 1.3 seconds, 1.4 seconds, and 1.5 seconds) respectively, with the depth of water (d) used which is 17.5 cm, 21 cm, and 24.5 cm, stroke variations as a wave generator are 4, 5, and 6 respectively. Wave period (T) and water depth (d) strongly influence the resulting wave characteristics in terms of wave height (H) and wavelength (L) values. The relationship between wave steepness (H/L) and period (T) has a difference between the two, with H/L being greater at a depth (d) of 24.5 cm than at depths (d) of 21 cm and 17.5 cm.

Abstract: The Ponorogo-Ngawi groundwater catchment area encompasses seven regencies in Central and East Java. Ngawi Regency, the largest rice producer in East Java (6.39 tons/ha), uses groundwater from the groundwater catchment area for irrigation. Increased agricultural productivity has been linked to the growing demand for groundwater. Excessive groundwater extraction can reduce both quantity and quality. To maintain groundwater availability, the Ngawi Regency requires proper planning and management. This study aimed to comprehend the water flow patterns within aquifers by creating a conceptual hydrogeological model. Geological and hydrogeological analyses were also conducted. The geological analysis is based on mapping and borehole data, whereas hydrogeological analysis relies on well measurements, water-quality tests, and water-balance analyses. The hydrogeological conceptual model of the research area describes the lithology as comprising lava, claystone, limestone, tuff, volcanic breccia, sandstone, and alluvium. Volcanic breccia and sandstone act as aquifers. The research area features confined and unconfined aquifers, with the groundwater level elevation in the research area ranging from 43.3 to 611.62 m above sea level. Groundwater flow patterns move from Mount Lawu towards the Bengawan Solo and Madiun Rivers and from the northern hills towards the Madiun River, with a groundwater recharge of 604 mm per year.

Abstract: Salinity fluctuation is a common condition in estuarine areas, which are places where sea water masses mix with fresh water. One of them is the Palu River estuary located in Lere Village, Palu City, Central Sulawesi. The influx of seawater into the river has decreased the important function of the river as a support for daily life, aquaculture, and transportation for fishermen. Based on this, this study was conducted with the aim of knowing the distribution of salinity in the Palu River estuary. Data were collected at 11 observation stations from October 24, 2022 to October 26, 2022, horizontally. Data processing used ODV (Ocean Data View) 4.0 software, and ArcGis 10.8. The research results from the distribution of salinity at 11 observation stations horizontally ranged from 3.63 to 36.10 ppt.

Abstract: The Northern Slope of Lawu Volcano has great groundwater potential and is widely used for agricultural irrigation. During the dry season, rainfed agricultural land relies on groundwater extracted from deep wells to fulfil its irrigation water requirements. However, this practice has led to a decline in the groundwater table in the shallow wells used by the local community. Effective groundwater management is essential to strike a balance between groundwater extraction and recharge. The objective of this study is to identify groundwater recharge areas on the Northern Slope of Lawu Volcano. The research methodology involves collecting samples of rainwater and groundwater for the analysis of stable isotopes, specifically Oxygen-18 and Deuterium. These stable isotope values are employed to determine the source of the groundwater. Rainwater samples were taken at seven different elevations, with a range between 54 and 1,052 meters above sea level (masl), to form the Local Meteoric Water Line (LMWL). In addition, groundwater samples were taken to determine groundwater sources, consisting of four samples of spring water, two samples of dug wells, and four samples of deep wells. The results of this study are expected to reveal that the water recharge area originates from an altitude of around 1,500 to 2,900 masl. These findings serve as an initial step in identifying the location of the groundwater protection zone for converse the sustainability of groundwater resources on the Northern Slope of Lawu Volcano.

Abstract: Population increment, and agricultural sector expansion in West Limboto, Gorontalo Regency, Indonesia, affect waste or pollutant increase. The community uses shallow groundwater as the main water source. Since shallow groundwater is vulnerable to pollution due to its depth and community activity, this study aims to identify its vulnerability in West Limboto. It was identified using the Groundwater Confinement, Overlying Strata, and Depth to Groundwater (GOD) Method. Those are also the parameters to be considered. The first parameter needs the aquifer-type data; the more unconfined the aquifer, the higher the index value. The second parameter needs the lithology data covering the stratigraphic aquifer, which is the high permeability lithology will have a higher index value. In comparison, the third parameter needs groundwater table data, which is the nearest to the ground surface, the higher the index value. The analysis shows that the Groundwater Vulnerability Index in the southern part of the study area is 0.5 – 0.7. It means that the aquifer is highly vulnerable to many pollutants. While at the middle to the northern part of the study area have an index of groundwater vulnerability in the range of 0.1 – 0.3, which means that the aquifer is vulnerable to conservative pollutants only. Therefore, the groundwater vulnerability of the study area was classified into 2 classes, the high index was in the southern part, and the low index was in the middle to the northern part of the study area.

Abstract: The Palu River estuary is a potential area for the socio-economic development of the surrounding community. The problem that often occurs in the river estuary is siltation due to the sedimentation process. The purpose of this research is to analyze the condition of the current pattern of the Palu River estuary against tides and river discharge that affect the sedimentation process in the estuary. The current pattern in the estuary was analyzed with a 2D mathematical model using MIKE ZERO software. This study used tidal, bathymetry and river discharge data. Three river discharge conditions were used, namely maximum conditions, normal conditions, and minimum conditions, which were obtained from field measurement data. The results of the analysis of this study showed that the type of tide that occurs in the Palu River estuary is a mixed type of double daily inclination. The tidal current pattern at the mouth of the river is dominated by the river discharge current. Minimum discharge current moves at a speed of 0.015-0.026 m/s, normal discharge current moves at a speed of 0.025-0.035 m/s, maximum discharge current moves at a speed of 0.031-0.051 m/s. The current pattern that occurs when the maximum discharge is the direction of the vector that moves away from the river. At high tide, the tidal current pattern moves towards the mouth of the river and is blocked by the river current so that there is a deflection of the tidal current. The accuracy level of the model results based on the RMSE value is 12%, this value can be categorized as good for the accuracy level.

Abstract: The Dumoga area, which includes the districts of Dumoga, West Dumoga, East Dumoga, Central Dumoga, South-east Dumoga, and North Dumoga in Bolaang Mongondow Regency, North Sulawesi Province, is an agricultural area that relies on groundwater for agricultural irrigation. To ensure the sustainability of the groundwater resources, it is crucial to protect the recharge areas. This study aimed to determine the locations of groundwater recharge areas in the Dumoga region using stable isotopes, specifically oxygen-18 (18O) and deuterium (D). Measurements of groundwater levels (GWL) were conducted to understand the direction and flow of groundwater, while measurements of electrical conductivity (EC) and groundwater temperature served as supporting parameters to assess the groundwater conditions in the research area. The findings revealed that the groundwater in the Dumoga region originates from the surrounding hills, with estimated recharge areas in surronding hills ranging in elevation from 326 meters above sea level (masl) to 462 masl.

Abstract: The Jeneberang watershed area is known for being susceptible to landslides. A field survey conducted in the Jeneberang watershed basin revealed that the slopes of andesite rock inclined up to 66°. Additionally, the rocks forming the slopes were found to be jointed. It is necessary to analyze slope stability and potential landslides at the study site. Some of the required data for this study include geological conditions, slope geometry, physical and mechanical properties of the rock from laboratory tests, and previous research findings. Slope modeling was conducted using Bishop’s limit equilibrium method in the Slide software to determine the Safety Factor (FS) value. Additionally, the Dips software was used to perform kinematic analysis and identify the type of landslides via stereographic projections. The slope is made up of andesitic and igneous rocks based on the analysis. The kinematic analysis of the stereographic projection results suggests that landslides on the research slope will occur in the direction of N 302° E. The type of slide that can occur on the slope is a plane (planar) type of slide. The safety factor of 4.1 indicates slope stability at the site, with little chance of sliding.

Abstract: Expansive soil is strongly influenced by the water content inside the soil particle , the significant changes of moisture content cause volume changes. The swelling and shrinkage potential of the soil can be indirectly identified by running the consistency limits test which are by controlling the plasticity index (IP) value and shrinkage limit (SL) value. This research aims to determine the value of liquid limit (LL), plastic limit (PL), plasticity index (IP), and shrinkage limit (SL) of soil-bentonite mixtures as expansive soil materials and analyzing the expansion potential of the modificated materials by its value. There were 5 variations of mixtures which are original soil (S), bentonite (B), 25%S+75%B, 50%S+50%B and 75%S+25%B. The results show the properties of soil-bentonite mixtures. The specific gravity and the grain size distributions were not significantly affected by the increase of the amount of bentonite. LL,PL and PI value significantly increase while SL value were decreased. Along with the increase of bentonite percentage, the activity value also increased by 1.5 to 4. It summarizes that by adding bentonite on the original soil, the expansion potential of the soil mixtures also increased.

Abstract: This paper presents rock mass classification for the empirical design of the excavation method and tunnel construction support system at Rongkong Dam, South Sulawesi, Indonesia. An evaluation of core drilling along the tunnel for analyzing the subsurface geological conditions. The Japan Society of Civil Engineers (JSCE) and Rock Mass Rating (RMR) were used to classify rock masses and suggest the reinforcement system and underground excavation. Based on the JSCE, the rock masses along the tunnel were categorized as CI and CII classes, by the RMR method, categorized as poor and fair quality. The RMR system recommends an excavation method for poor to fair rock mass quality: top heading and bench. Meanwhile, in the JSCE system, the excavation method is full-face with an auxiliary bench cut. The RMR method recommends the following support systems for tunnel portals because the stand-up time value of the rock mass was relatively low: rock bolts with a diameter of 20 mm, length of 4-5 m, spacing of 1.0-1.5 m, and shotcrete thickness of 100-150 mm on the crown and 100 mm on the walls, as well as steel sets with a length 1.5 m. According to the JSCE system, the most recommended reinforcement system for the conditions in the research region comprises rock bolts measuring 4 m long and 1.2 m in spacing along with steel beam H-150 spaced 1.2 m apart. Furthermore, 15 cm thick shotcrete and lining with thick 40 cm on walls and 45 cm on invert.