Vulnerability is a loss rate perceived from elements at risk owing to the impact of hazards on determined magnitude and frequency. Vulnerability assessment of elements at risk is a critical component in the risk assessment framework. Considerable studies regarding flash floods have been conducted, but the depth of information on vulnerability is still limited. This study presents a model of the physical vulnerability of buildings caused by the incidence of flash floods, which is strengthened through intensity of the impact process and loss. This model used a non-linear regression approach using behavioural data in the form of the propagation height of the flood. The order-2 polynomial distribution can represent the relationship between the magnitudes of the best process and loss rate. The results are the risk assessments of an exposed area in mitigation strategies.

Previous researchers have been widely studied the equation for calculating the energy dissipation in USBR Type IV, applied in the stilling basin structure as an energy dissipator. However, inefficient energy dissipating basins are commonly found in the field due to the large discharge and high water head, potentially damaging the bottom of the energy dissipating basin and its downstream river. Therefore, an energy dissipator plan fulfilling the safe specifications for the flow behaviour that occurred is required. This study aimed to determine the variation of the energy dissipators and evaluate their effect on the hydraulic jump and energy dissipation. For this purpose, a physical model was undertaken on the USBR Type IV spillway system. The novelty of this experiment showed that combination and modification dissipation features, such as floor elevation, end threshold and riprap lengthening, could effectively dissipate the impact of energy downstream. The final series exhibited a significantly higher Lj/y1 ratio, a favourable condition due to the compaction of the hydraulic jump. There was also a significant increase in the downstream tailwater depth (y2) during the jump formation. Therefore, the final series energy dissipator was better in the stilling basin design for hydraulic jump stability and compaction. The increase in energy dissipation for the final series type was the highest (98.4%) in Q2 and the lowest (84.8%) in Q10 compared to the original series. Therefore, this type can better reduce the cavitation risk damaging to the structure and downstream of the river.

The construction of the Keuliling Reservoir aims to accommodate and utilise water for agricultural purposes. In this research, soil erosion modelling using the USLE method showed that the level of erosion hazard for each Keuliling Reservoir sub-watershed was classified into low-moderate. Land erosion occurred in the area around the reservoir inundation is the most significant contribution to the magnitude of erosion (38.62 Mg∙ha–1∙y–1. Based on the point of sediment sampling in the Keuliling reservoir, the sediment volume was 1.43 Mg∙m–3. So, the volumetric sediment input from the Keuliling reservoir watershed is 20.918,32 m3∙y–1. The degradation of reservoir function due to sedimentation can affect reservoir services. The ability to estimate the rate of watershed surface erosion and sediment deposition in the reservoir is vital for reservoir sustainability. Besides the land erosion in the Keuliling Reservoir, there are also other potential sources of erosion that can reduce the capacity of the reservoir, i.e. the rate of sedimentation from a reservoir cliff landslide. The USLE estimation results show that the soil erosion analysis provides important and systematic information about nature, intensity and spatial distribution in the watershed and sediment volume in the Keuliling Reservoir. This finding allows the identification of the most vulnerable areas and the type of erosion dominant for long-term land management.

Erosion and sedimentation have a very big influence on flooding. Floods are strongly influenced by land use and population activities that change the river’s physical condition, including erosion and sedimentation. The river upstream was very steep, and the downstream was narrowing and meandering with high rainfall recorded. This study analyses erosion, sedimentation, and its handling using the eco-hydraulic base. The method involves input rainfall data, river hydraulics, land use, watershed area, and land cover. The analysis of hydrology, hydraulics, land use, flood discharge, and eco-hydraulic, inundation height, vegetation diameter, velocity reduced, and riverbank width measured in five bridges cross-sections along the river. The eco-hydraulic compares the width of existing riverbanks and design, high inundation, and the vegetation diameter to minimise flood discharge. Erosion in the right cliff is 22.73% and the left cliff is 37.04%, land erosion was 225.83 Mg∙ha –1∙year –1. The river’s bottom is formed by rocks of 0.18–1.30 mm. The plantation land used around the Lae Kombih River grows mainly an oil palm with a diameter of 0.5–0.7 m. The riverbank design on 100 m for vegetation diameter of 0.1–1.0 m can retain flood discharge for five years return period up to 72.3%, resulting in discharge of 112.04209.43 m 3∙s –1. The largest erosion and sedimentation on the river border is Dusun Silak, so it is recommended to plant Vetiveria zizanioides, Ipomoea carnea and Bambusoideae. An inundation height of 0.9 m can be recommended to design an embankment to be used as flood mitigation.

Sedimentation is commonly found as one of the problems affecting the function of reservoirs in Indonesia. High risk soil erosion leads to the increase in sediment production which negatively influencing the capacity or functional age of the reservoir. Generally, several reservoirs in Indonesia are experiencing the operational problem due to the increasing of sedimentation throughout the year. The data presented in this article was obtained from the measurement of sediment in the area of Keuliling reservoir, including: The data of suspended sediment at every Keulling reservoir water inlet, the data of bedload sediment at the bottom of the Keuliling reservoir, the hydrometric data, including the water velocity and channel profile, where the sampling of bedload and suspended sediment sampling was conducted at each inlet. the data sediment volume at the dam reservoir. The data of suspended and bedload sediment were obtained by taking the samples and analyzed in a laboratory. The measurement was conducted three times in five months. The data of water velocity was also generated based on the measurement using a currentmeter. Meanwhile, the sediment volume data in the water storage of reservoir was gathered by conducting a bathymetry and topographic survey at the dam reservoir location and then comparing it with the pre-existing bathymetry and topographic data.

The Sianjo-anjo reservoir is used to meet the need for downstream clean water. Land activity at the Sianjo- anjo reservoir watershed can potentially increase the rate of erosion and the silting of rivers and reservoirs due to sedimentation. Reservoir siltation is a crucial challenge for reservoir management because it can reduce its function and affect its service life. However, sediment yield is often overlooked in reservoir planning and environmental assessment. This study aims to predict the rate of land erosion and sediment yield, and create an erosion hazard map of the Sianjo-anjo reservoir watershed. The study used a Geographic Information System, GIS-based Universal Soil Loss Equation (USLE) method and discovered that the erosion rate of the Sianjo-anjo reservoir watershed was between 35.23 Mg∙ha –1∙y –1 until 455.08 Mg∙ha –1∙y –1, with 95.85% classified as the low level, 0.03% as moderate, and 4.12% as high. Meanwhile, the sediment yield from the Sianjo-anjo reservoir watershed was 218,812.802 Mg∙y –1. USLE is vital to identify areas susceptible to erosion and crucial for reservoir sustainability. Furthermore, it is necessary to plan good sediment management. Long-term land conservation is required to maintain storage capacity and ensure effective operation of the reservoir.