Indonesia’s flash floods have increased significantly since the flash flood in Bohorok, North Sumatra, in 2003 and Jember, East Java, in 2006. Such flash floods have caused negative impacts, loss of human life and damage to vital infrastructures such as houses, roads, bridges, or other public facilities. Understanding the factors driving flash floods and their mechanism at the outset is essential in mitigating the negative impacts mentioned above. This paper presents the results of the analysis of the flash flood characteristics of several hydraulic parameters under conditions just before the flash flood incident, including the intensity of the rainfall, the time of concentration, and the time lag of the occurrence. As the object of the study, a flash flood event was selected in Batu City, Upper Brantas River, which occurred on November 4, 2021. The results show that the lag time of the flash flood occurrence at 40 minutes magnitude at Bulukerto Village of Batu City, the application of Kirpich for the time of concentration equation performed better than the Ventura and Watt & Chow equations. Further assessment of precursory characteristics for other similar small catchment and hydro-meteorological conditions is still the subject of beneficial study or research.

The development of dams or reservoirs requires continuous attention. The dynamics of rain as the primary natural resource and the water utilization may change from the design. Climate change is thought to have caused changes in reservoir inflow patterns where the patterns may change throughout the service life of the reservoir. The way of the utilization of catchment areas and reservoir inundation is also very dynamic, along with the dynamics of water demand which is generally aimed at obtaining better human welfare. At the same time, such activities may affect the quality of the reservoir waters, followed by disturbances in the water utilization for various purposes. This paper presents the results of evaluating the carrying capacity of the reservoir environment based on the data obtained from reservoir sedimentation and water monitoring of Kedungombo Reservoir. The adopted method of the environmental carrying capacity of the Kedungombo Reservoir considers the four environment-related carrying capacities, i.e., reservoir sedimentation, water utilization, recreation, and aquaculture. The term overall carrying capacity is introduced, adopting three approximations of weighting factor α of the four parameters. The analysis results show a promising method to evaluate the reservoir environment carrying capacity that could be dynamics during its service life.