Article

Estimation of the Relative Severity of Floods in Small Ungauged Catchments for Preliminary Observations on Flash Flood Preparedness: A Case Study in Korea

Department of Civil Engineering, Sunmoon University, 100 Kalsan-ri, Tangjeong-myeon, Asan-si, Chungnam-do 336-708, Korea.
International Journal of Environmental Research and Public Health (Impact Factor: 2.06). 04/2012; 9(4):1507-22. DOI: 10.3390/ijerph9041507
Source: PubMed

ABSTRACT

An increase in the occurrence of sudden local flooding of great volume and short duration has caused significant danger and loss of life and property in Korea as well as many other parts of the World. Since such floods usually accompanied by rapid runoff and debris flow rise quite quickly with little or no advance warning to prevent flood damage, this study presents a new flash flood indexing methodology to promptly provide preliminary observations regarding emergency preparedness and response to flash flood disasters in small ungauged catchments. Flood runoff hydrographs are generated from a rainfall-runoff model for the annual maximum rainfall series of long-term observed data in the two selected small ungauged catchments. The relative flood severity factors quantifying characteristics of flood runoff hydrographs are standardized by the highest recorded maximum value, and then averaged to obtain the flash flood index only for flash flood events in each study catchment. It is expected that the regression equations between the proposed flash flood index and rainfall characteristics can provide the basis database of the preliminary information for forecasting the local flood severity in order to facilitate flash flood preparedness in small ungauged catchments.

    • "Floods cause damages and deaths (casualties, property losses and environmental damages) in the world and always need innovative models such as artificial neural networks (ANNs) and support vector machines (SVM) to forecast (the time, place and magnitude of the event) and warn it. Numerous floods are reported in Malaysia (Alaghmand, 2012), USA (Johnson, 2000), Oman (Al-Rawas, 2009), Korea (Kim and Choi, 2012), Europe (Gaume, 2009; Sauvagnargues-Lesage and Ayral, 2007) and Iran (Golian, 2010), which require innovative measures to diminish their impacts. In addition, because of the climate change, floods are deliberated one of the most significant rising natural threats of the world (Choi, 2004; Hegedüs et al., 2013). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Floods always require innovative models for flood forecasting. This paper proposes a dynamic artificial neural network (DANN) model for evaluating land-use change impact (LUCI) scenarios on weighted average of warning lead-time of flood (WAWLTF) in an urbanised watershed. The simulated floods of a calibrated HEC-HMS hydrological model were used for training and testing of DANN model. The features of proposed DANN's structure were determined by minimisation of a new flood forecasting error(FFE) index. Results showed that the proposed procedure was able to optimise features of DANN structure by minimising FFE and produced an appropriate DANN model for assessment of LUCI on WAWLTF. The results also denoted that practicing suitable watershed management in future may improve WAWLTF encouragingly but never compensates negative impact of urbanisation completely. In conclusion, the model can be used as an efficient tool in similar urbanised watershed for assessment of LUCI on WAWLTF.
    No preview · Article · Jan 2015 · International Journal of Hydrology Science and Technology
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ahn, Jae Hyun and Hyun Il Choi, 2013. A New Flood Index for Use in Evaluation of Local Flood Severity: A Case Study of Small Ungauged Catchments in Korea. Journal of the American Water Resources Association (JAWRA) 49(1): 1-14. DOI: 10.1111/jawr.12025 Abstract: The aim of this article is to develop a new index measuring the severity of floods in small ungauged catchments for initial local flood information by the regression analysis between the new flooding index and rainfall patterns. Although a rapid local flood caused by heavy storm in a short period of time is now one of common natural disasters worldwide, such a sudden and violent hydrologic event is difficult to forecast. As local flooding rises rapidly with little or no advance warning, the key to local flood forecasting is to quickly identify when and where local flooding above a threshold is likely to occur. The new flooding index to characterize local floods is measured by the three normalized relative severity factors for the flood magnitude ratio, the rising curve gradient, and the flooding duration time, quantifying characteristics of flood runoff hydrographs. The new flooding index implemented for the two selected small ungauged catchments in the Korean Peninsula shows a very high correlation with logarithm of the 2-h maximum rainfall depth. This study proposes 30 mm of rainfall in a 2-h period as a basin-specific guidance of precaution for the incipient local flooding in the two study catchments. It is expected that the best-fit regression equation between the new flooding index and a certain rainfall rate can provide preliminary observations, the flood threshold, and severity information, for use in a local flood alert system in small ungauged catchments. Editor's note: This paper is part of a featured series on Korean Hydrology. The series addresses the need for a new paradigm of river and watershed management for Korea due to climate and land use changes.
    No preview · Article · Feb 2013 · JAWRA Journal of the American Water Resources Association
  • [Show abstract] [Hide abstract]
    ABSTRACT: A flash flood caused by heavy storm in a short period of time is now one of the common natural disasters worldwide. The aim of this paper is to develop a new flood hazard index for use in local flood severity predictions in small ungauged catchments through the regression analysis between the flood hazard index and rainfall features. The flood events with the peak flow above a threshold discharge are targeted to estimate the flood hazard index among the annual maximum flood runoff hydrographs generated from a rainfall-runoff model for the long-term-observed rainfall data. To quantify characteristics of flood runoff hydrographs simulated for ungauged catchments, the new flood hazard index is measured by the average of the three normalized relative severity factors, such as the flood magnitude ratio, the rising curve gradient, and the rising average runoff to the peak time. The proposed flood hazard index shows a high correlation with logarithm of the short-duration rainfall for the two selected small ungauged catchments in the Korean Peninsula. The best-fit regression equation between the flood hazard index and rainfall patterns can be used in predicting the relative flash flood severity for small ungauged catchments.
    No preview · Article · Sep 2015 · Natural Hazards