Rainfall is one of the common triggering factors of the flood. Bandung City is located in the Upper Citarum river basin. Parts of the city, such as Bojong Sari, Bojong Soang, Cieunteung and Andir Sub district, are in natural floodplains. During the wet season, these areas are frequently flooded. This study analyzed the critical rainfall level that potentially caused flooding. The Hydrologic Engineering Centres Hydrologic Modelling System (HEC-HMS) rainfall-runoff model and the 1D HECRAS model were applied. A six storm pattern was simulated to determine the critical rainfall that generated the water depth that was equal to or greater than the critical water surface depth at specific points in the river. Hypothetical rainfall events are used to investigate the response of the river basin at critical cross-sections. It can be considered by different temporal distributions. The amount of rainfall is assumed to be distributed uniformly. The conclusion of this research is that the storm pattern (rainfall depth and rainfall duration) plays a crucial role in determining the critical rainfall at the flood location. The critical rainfall in a specific location is affected by the position at the river cross-section (in the upstream or the downstream area) and the bank full capacity of the river cross-sections.

Derivation of the critical rainfall level needed for an early flood warning in the upper citarum river basin indonesia

In recent years, flash floods have increased, accompanying rapid economic growth, changes to the natural environment and increases in extreme climate events. However, spatial heterogeneity in the influencing factors has seldom been studied systematically. This paper investigates this issue by using the Geodetector tool and considering 14 factors such as climate, natural environment, and human activities in 11 ecoregions in China based on flash flood records from 1950 to 2015 collected by the Investigation Project of Chinese Flash Floods. The results showed that there is obvious spatial heterogeneity in the main influencing factors and influencing weights in 11 ecoregions. Precipitation and landforms have the greatest effects on flash floods and the interactions of these two factors have the strongest effects as compared to interactions between other factors in most of the 11 ecoregions; however, the effect has obvious variation from northwest to Southeast. Meanwhile, human activities were found to have tangible impacts, especially in ecologically vulnerable regions. The findings provide a new understanding of how and why flash floods occur in a particular region and contribute to the formulation of regionally targeted strategies to cope with flash flood.

https://www.mdpi.com/2073-4441/12/12/3344/pdf

Why Flash Floods Occur Differently across Regions? A Spatial Analysis of China

Critical rainfall estimation for early warning of rainstorm-induced flash flood is an inverse rainstorm-runoff process based on warning discharge threshold for a warning station of interest in a watershed. The key aspects of critical rainfall include rainfall amount and rainfall duration. Storm pattern affects highly the estimation of critical rainfall. Using hydrological modeling technique with detailed sub-basin delineation and manual for design rainstorm-runoff computation, this study first introduced basic concept and analysis methods on critical rainfall for flash flood early warning, then, investigated the responses of flash flood warning critical rainfall to storm pattern. Taking south branch of Censhui watershed in China as an example, critical rainfall in case of typical storm patterns for early warning of rainstorm-induced flash flood were estimated at 3 warning stations. This research illustrates that storm pattern plays important role in the estimation of critical rainfall and enough attention should also be paid to storm pattern when making a decision on whether a warning to be issued or not.

Miao

Papers

Response of Flash Flood Early Warning Critical Rainfall to Storm Pattern in South Branch of Censhui Watershed