Extremely heavy rainfall associated with super typhoon Ragasa could cause the Matai-an landslide dam to overtop in the next two days.
In East Asia, super typhoon Ragasa is moving westwards between Taiwan and the Philippines. At the time of writing, Earth Cut TV has a live feed from the Batanes Islands, almost in the path of the eye (although there is a good chance that data connectivity will be lost in the storm):-
This is an exceptional storm, bringing heavy rainfall and strong winds to a wide area.
The storm has the potential to bring extremely heavy rainfall to southern and eastern Taiwan. There is huge uncertainty as to the magnitude, but reports indicate that the Central Meteorological Administration has estimated that precipitation totals as high as 800 mm could be seen in the mountain areas of Hualien County.
As I have highlighted previously, there is a large valley-blocking landslide at Matai’an in Hualien County, with a large volume of water steadily accumulating. The image below, released by the Hualien Branch of the Forestry and Conservation Department, shows the level of the lake relative to the landslide dam:-
As the image above shows, the freeboard is now quite low.
In consequence, the Forestry and Conservation Administration of the Ministry of Agriculture issued a red alert at 7 a.m. this morning (22 September), mandating the evacuation of vulnerable households downstream. It is estimated that this affects around 1,800 homes.
Should overtopping occur, it is anticipated that 24 September would be the most likely date, so we will need to watch with interest. The Central Weather Administration maintains an exceptional set of web resources recording accumulated precipitation in Taiwan.
Overtopping is not inevitable in the next few days, but that will almost certainly occur in the next few weeks. It is going to be fascinating to see what happens.