Tropical Storm Washi, known locally as Sendong, caused heavy damage in the northern parts of Mindanao, the Philippines on 17 December 2011, resulting in the worst disaster in the history of Mindanao. The most seriously affected were Cagayan de Oro city along Cagayan de Oro river and Illigan city along Mandulog river. 1,268 persons were dead, 181 missing, and 51,144 houses were damaged (totally 13,585 and partially 37,559) according to Final Report of the National Disaster Risk Reduction and Management Council on 10 February 2012.
The heavy damage is attributed to the extremely high flood levels with a great deal of sediment/wooden debris which swept away/destroyed settlements densely developed on the flood plains and islands in and around the two major cities. Picture 1 and 2 show flood plains where settlements have been washed away. Picture 3 indicates flood level higher than the roof of two stories house. Picture 4 shows wooden debris accumulated near the Mandulog river mouth.
The Philippines has a good experience of constructing the open (slit) type sabo dam to deal with sediment/wooden debris. Sabo dams constructed after the disaster in Ormoc City, Leyte in November 1991 have been successful to protect the city thereafter from disasters even with more intensive rainfall than that of 1991. Picture 6 shows damage by debris in 1991 floods and picture 7 shows effectiveness of a sabo dam in the case of floods in July 2003.
Picture 1 : Flood plain where settlements disappeared by floods
Picture 2: Damage to a bridge and settlements along the river
Picture 3 : Houses were damaged by floods exceeding two story house
Picture 5 : Missing person data collection center, Illigan City
Picture 6 : Damage by floods with much wooden debris in 1991, Ormoc, Leyte
Picture 7 : A sabo dam which seized debris at the time of floods of 2003, Ormoc, Leyte
Track of Tropical Storm "SENDONG"
Final Report on the Effects and Emergency Management re
Tropical Storm "SENDONG" (Washi)