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Hydrological drought analysis in a river basin is crucial because it impacts water resource management, agriculture, drinking water supply, industry, ecology, and disaster risk mitigation. It plays a key role in water usage planning, safeguarding agricultural yields, and ensuring a stable drinking water supply. In the context of this research, the Corong River basin is used as a case study. This study aims to determine the level of hydrological drought (deficit) using the Threshold Level Method (TLM) and predict hydrological drought using the Seasonal Autoregressive Integrated Moving Average (SARIMA) model. This model understands the characteristics of drought and predicts drought in the Corong River basin for early mitigation and anticipation of drought in the region. The results of this research indicate a strong relationship between the Hydrological Drought Index (HDI) and streamflow and Precipitation (PRCP), which can be used to forecast future droughts. This model is highly robust and accurate in observing the level of hydrological drought (deficit, duration, and sharpness) and predicting drought events in the Corong River basin. These findings have significant practical implications for water management and disaster risk mitigation in this river basin while also advancing the scientific understanding of hydrological drought. [ABSTRACT FROM AUTHOR]

Natural disasters are common worldwide, especially in tropical countries. Floods are one such frequent disaster that occur in the tropical country of Indonesia. Floods cause disasters in many vulnerable societies living in the area. Therefore, it is necessary to conduct risk assessments for flood mitigation. The objective of this research is to support decision-making for flood risk assessment by selecting priority sub-systems. The research was conducted in Surabaya, East Java, and Indonesia. The Surabaya drainage system is divided into five districts consisting of several sub-systems facing inundation problems. This causes challenges for the government in selecting which sub-systems should be prioritized to overcome these problems. Consequently, a rank priority for sub-systems is required. This research validated whether the Analytics Hierarchy Process (AHP) method was applicable and appropriate to weight priority factors to select the priority drainage system. It weighs historical flood data by considering several criteria related to floods, consisting of flood hazards, social economics, and the environment. Flood hazard is defined as the severity level of flooding indicated by three indicators: inundation area, inundation depth, and inundation duration. Social-economics is a criterion covering population density and land use types consisting of residential areas, commercial and services areas, public facilities, industrial areas, port areas, and mix used development support areas. Environment is a criteria indicated by green open space, flood-prone areas, watershed catchment areas, and storage areas. The weighting result convinced the decision makers as to the related parameters which should be considered in order to support appropriate and effective flood mitigation. Further, due to budget constraints, the results of the research can be used to assist the municipal government in selecting which drainage system should be prioritized for management. The AHP result reveals that the priority drainage systems are Wonorejo sub system (Jambangan district), Greges sub system (Genteng district), Kedurus sub system (Wiyung district), Kalibokor sub system (Gubeng district), and Tambak Dono sub system (Tandes district). The result was confirmed to several respondents from Department of Public Works, Highways, and Drainage Management involved with the drainage system in Surabaya. It is indicates that the AHP results mostly are applicable to the existing condition. [ABSTRACT FROM AUTHOR]

This research is aimed to assess the sediment transport rate under different conditions of estuary geometry by comparing the situations before and after the construction of Sembayat Weir. Sediment concentration, flow velocity, and temperature were obtained via field investigation from October 2016 to September 2017. River discharge and tidal discharge phenomenon are analyzed in the estuary, which affect hydraulic head changes. The HEC-RAS model was used for numerical modelling simulation of the hydrodynamics. The results revealed that the sediment transport rate increased under the influence of erosion in the river branches. BH2 and BH3 were the observation sites located before and after the tributary junction. Those location present the sediment transport rates decreased by 30% and 26%, respectively, in the rainy season because after weir construction. The results agree with previous research results in that sediments were deposited around the estuary weir. Meanwhile, in the river branches, a higher sediment transport rate was observed because of the tidal current that provided sediment transport over a longer term in the dry season. The findings extend the knowledge on the influence of Sembayat Weir on sediment transport rate characteristics with respect to seasonal changes. [ABSTRACT FROM AUTHOR]