Dian Sisinggih

Reservoir sedimentation threatens the long-term performance of multipurpose dams, especially in cascade systems where upstream flushing may intensify downstream deposition. This study aimed to diagnose sediment regime transformation in Sutami Reservoir within the Sengguruh-Sutami cascade system, East Java, Indonesia. An integrated framework combining the Borland–Miller empirical area reduction method (EARM), bathymetric differencing, and two-dimensional hydrodynamic modelling using the two-dimensional hydrodynamic-sediment transport solver in iRIC (Nays2DH) was applied using historical profile data (1972–2021) and bathymetric surveys from 2016 and 2021. The analyses showed that approximately 8.50 ∙ 106 m3 of sediment was redistributed during 2016 to 2021, with about 62% accumulating below elevation 240 m, while the zero-capacity elevation rose by 0.24 m. Bathymetric differencing indicated a net storage loss of 7.06 ∙ 106 m3 and confirmed downstream migration of deposition into the mid-reservoir and near-dam zones. The hydrodynamic simulation was used qualitatively to identify transport mechanisms rather than to hindcast the cumulative five-year sediment budget, and it showed that density-driven sediment plumes generated during upstream flushing can bypass shallow delta zones and promote deposition in deeper parts of the reservoir. The combined evidence indicates that the sediment distribution pattern in Sutami Reservoir has shifted from predominantly upstream/delta deposition toward increasing deposition in the deeper parts of the reservoir, broadly corresponding to a transition from Type I toward Type III–IV Borland–Miller distribution characteristics. So sedimentation in Sutami cannot be interpreted as an isolated single-reservoir process and support the need for coordinated cascade scale sediment management.

Reservoir water balance assessment is essential for understanding how climate variability and climate change affect water availability and operational performance in monsoon regions. This study evaluates baseline (2006–2023) and projected (2024–2050) water balance stress in Wonogiri Reservoir, Indonesia, using bias-corrected Coordinated Regional Climate Downscaling Experiment for Southeast Asia (CORDEX-SEA) projections under representative concentration pathways (RCP4.5 and RCP8.5). The main contribution is an integrated reservoir-scale framework linking artificial neural network (ANN)-corrected precipitation and potential evapotranspiration with hydrological inflow simulation and differentiated forecasting of turbine and hollow jet valve (HJV) outflows to assess intra-annual storage stress under an operational constraint. An ANN was applied for bias correction and coupled with the F.J. Mock model for inflow simulation, while singular spectrum analysis (SSA) was used for outflow forecasting. Water balance was evaluated under probabilistic hydrologic conditions with a minimum intake elevation of 128 m. Baseline results indicate a monsoon-driven surplus–deficit regime with high inflow variability (0.04–221.93 m3∙s−1) and strong dry-season vulnerability due to elevated evapotranspiration. The SSA shows higher predictability for turbine outflows (NSE = 0.76) than for HJV outflows (NSE = 0.58). Although dependable inflow increases in both scenarios, these gains do not translate into higher effective storage. Instead, additional inflow is largely discharged during wet periods, while dry-season storage declines because of unfavourable inflow timing and increased evaporation. Thus, climate change may intensify seasonal operational stress, requiring adaptation strategies focused on seasonal timing, evaporation losses, and release pathways rather than annual water availability alone.

Cavitation in high-velocity spillways is a critical issue in modern hydraulic design, particularly in channels with downward concave vertical curvature, which are vulnerable to negative pressure and jet reattachment. This study aims to evaluate the influence of aerator position, using a deflector-groove type, on flow characteristics, pressure distribution, entrained air mass, and the cavitation index in a multi-slope spillway through CFD-based numerical simulation. Five aerator configurations, labeled A to E, were analyzed under a design discharge of 1,154.3 m³/s, using the SST k–ω turbulence model and mesh sizes ranging from 220 to 500 mm. Validation against physical data showed a high level of significance, with R² > 0.9, confirming the reliability of the numerical model used. The velocity distribution indicates that the aerator location significantly influences air-jet formation and air-cavity stability. The aerator positioned at the center of the concave section, Series A, produced the most stable flow pattern, controlled negative pressure, and an entrained air mass of 63 kg/s. In addition, the cavitation index value for Series A showed an average increase of up to 20% compared with the other configurations, indicating the effectiveness of this position in reducing cavitation potential. Based on the integrated results of pressure, aeration, and cavitation index, the Series A configuration is recommended as the optimal position for spillways with a downward concave vertical curve geometry. This finding reinforces the established aeration theory reported in previous studies and provides a practical contribution to the optimization of aerator design in complex spillways.

Because channel bends alter the velocity, force, and path of water and sediment, meandering rivers exhibit strong local variations in flow, sediment movement, and bed shape. While sharp bends increase erosion on the outer bank and build-up on the inner bank, few large-scale studies isolate how bend sharpness affects separate water flows under shifting river shapes. To address this, the two-dimensional Nays2DH model in iRIC was used for a U-shaped section of the Kusan River in South Kalimantan, Indonesia, with a curve ratio sequence about 20–6–20, and tested with three flow rates. Notably, water hugged the outer bank with slow-moving water inside, showing clearer side-to-side differences in water level and velocity at the sharp bend (curve ratio = 6). The lowest Froude number was always near the end of this sharp bend, and in all cases, the velocity remained below critical velocity. Higher water flow increased both types of sediment movement, moved larger particles, and changed the bed more, while the bend shape determined where erosion and deposition occurred. Maximum erosion did not always happen at the sharpest bend, as water adjusted to the curve and moved downstream. These results show a practical division: water volume controls the size of riverbed changes, while bend shape controls their locations. Knowing this helps target areas for erosion control and better understand how bends change over time.

This research intends to build a 3-D flow model of a section of the spillway chute at Tigadihaji Dam under the spillway design flood with a 1000-year return period, to investigate flow behaviour and the potential of cavitation damage using a numerical model in Ansys Fluent. The numerical model is validated against a physical model, and the impact of the aerator on the chute is also assesses. The research parameters are velocity, pressure, and cavitation number, obtained from the measurements at 16 points along the chute. The methodology consists of modelling and validation. The modelling was carried out for the chute and the chute with an aerator. The validation of computational fluid dynamics (CFD) model, based on pressure data, produced a determination coefficient (R2) of about 0.97. It shows that the CFD model is very good in presenting the trend and fluctuation of physical data. The cavitation analysis at Q1000 indicates a moderate risk in chuteway-3 and a high risk in chuteway-4. To mitigate this, a deflector–offset aerator was installed at the slope transition from 1:35 to 1:1.5. The simulation results reveal an increase of up to 0.1 in the cavitation index, with improvements extending about 20 m downstream of the aerator. Nevertheless, the offset section on the milder curved profile limited performance due to incomplete aeration.

This research focuses on the development of a hydraulic model of energy dissipator with segmented end sill on the dam spillway as a modification of the standard United States Bureau of Reclamation (USBR) Type III design. By using Froude similarity analysis at 1:100 scale and a Froude number range of 13-25, this study compares the performance of the standard design (Configuration A) with a modification by using a two-segment zigzag pattern segmented end sill (Configuration B). The results show that Configuration B achieves a specific energy reduction of up to 15- 23% higher than Configuration A across all tested discharge ranges (9-22 l/s). The segmented end sill causes the increase of turbulence, the expansion of the vortex area, a more even distribution of energy, and then the reduction of the potential damage in the dam downstream. This research provides an efficient and economical design alternative for improving the safety of hydraulic structures in dams with high supercritical flow conditions.

This study aims to assess the current operational framework of the multi-purpose Ladongi reservoir, which serves various functions including providing 120 L/s of raw water, irrigating 3,600 ha of land, controlling floods, potentially generating 1.3 MW via a Mini Hydro Power Plant, and supporting the tourism sector. The evaluation utilizes measurements of the reservoir's capacity to satisfy various requirements classified by three indexes: reliability, resilience, and vulnerability. The results indicate that the existing framework of the Ladongi reservoir has a reliability of 92.72% with an average deficit ratio of 7% based on 23 years of historical data. Based on the current operational scheme, the reservoir has a fairly high level of reliability and resilience translating to a considerable recovery duration from a failed period. Additionally, the maximum deficit ratio reaches 100% suggesting that in that period the reservoir cannot meet the target despite that the average deficit ratio is small, highlighting the variables that need to be optimized in the operation framework.

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 land use characteristics in the Semantok watershed have a significant impact on the reservoir's usable age. According to the land use patterns, including teak woods, rice fields, moorlands, dry fields, and residential areas, the Semantok watershed has the capacity to carry sediment when it rains. One of the models to analyze surface runoff and sediment is the Soil and Water Assessment Tool (SWAT). SWAT was developed to predict the impact of land management practices on water, sediment and agricultural chemical yields in large complex watersheds with varying soils, land use and management conditions over long periods of time. The purpose of this research is to quantify the amount of erosion and sedimentation that results from land use changes in the Semantok watershed in 2015 and 2021 and to determine management scenarios that can reduce the value of erosion and sedimentation that can implemented upstream of the Semantok dam using SWAT. The data used for the research are climatology data, DEM map, landuse map, and river data. The amount of erosion at the Semantok watershed outlet increased from 7.00 mm/year in 2015 to 14.18 mm/year in 2021. Based on Forestry Ministerial Regulation No. P.61/Menhut-II/2014, the Semantok watershed's carrying capacity is 3.95 falling into the pretty bad category (3.5 < DDD < 4.3). Three scenarios were compared in order to carry out control efforts: revegetation, check dams, and combining revegetation and check dams. The most efficient way to reduce erosion by up to 30.51% is to combine revegetation and check dam.