FLASH FLOOD EVENTS IN MU CANG CHAI AND MUONG LA ON AUGUST 3, 2017 - CAUSES AND PREVENTION MEASURES

Abstract

In the early morning of August 3, 2017, the two flash flood events occurred in Kim Noi and Nam Pam watersheds in Mu Cang Chai and Muong La districts, respectively. The analysis of rainfall data and field surveys shows that the severe events related to extreme local rainfall (>100 mm in 6 hours) accompanying with steep topography (>40% slope) and low vegetation cover. Therefore, flood is formed fast with short concentration time. Furthermore, narrowing cross-sections on stream by 25-80% cause flow clog and temporarily generate small dams. When the amount of floodwater exceeded the capacity of these small dams, water from dam break generates flash flood and sweep everything in downstream. The paper aims to provide short- and long-term measures to prevent and reduce flash flood damages.