21 October 2010

The curious story of the Rajang log jam in Sarawak, Malaysia

Posted by Dave Petley

An interesting if somewhat strange story has developed in Malaysia over the last few days.  The Rajang River flows over a distance of about 560 km across Sarawak.  It is fairly obvious on this Google Earth image:

A fortnight ago reports emerged that there were navigation problems on the lower reaches of the river.   Unusually, these issues occurred not because of high or low river levels, but because the river was choked with wood (a logjam).  These impressive images, from http://hornbillunleashed.wordpress.com/2010/10/08/10352/ illustrate the magnitude of the issue.  The blockage reportedly extended for 250 km.

The reason that the wood entered the river appears to have been intense rainfall on 6th to 7th October, but the question is where the wood has come from.  There are two likely sources of wood like this.  The first is that a logging camp or store was inundated (unlikely on this scale); the second is extensive landslides.  In Malaysia right now a huge blame game is playing out over the cause of the disaster.  The Land Development Minister, James Masing, has claimed that the cause was logging in the catchment.  Meanwhile, the state forest director, Len Talif, is blaming shifting rainfall patterns.  

The source area appears to have been Sungai Melatai in the Balleh subcatchment, shown here:

Some reports suggest that there was a very large landslide event in this catchment:

A man from Sungai Melatai, a tributary of Baleh River, gave the following account of the cause.
“The cause of the ecological disaster and the extensive environmental damage has nothing to do with the rain or rising water level because on the day it happened the water level along Baleh River was low and normal. There was extensive landslide of between five and 10km on both banks of Sungai Melatai. This has nothing to do with farming activities. It is caused by human disregard for the environment through extensive logging activities.” A child died when its mother could not send it for medical treatment in Kapit due to the logjam. Two men in a Land Cruiser died in the landslide. 


When contacted, the Superintendent of Land and Survey Kapit Affin Bawi said the massive landslide was the culprit. His view was confirmed by an officer from Sarawak Rivers Board.  An elderly casual worker identified as Jilan explained that the Ibans described the phenomenon as ‘baruas’ or massive landslide affecting a huge area, when nature gives way.

It is clear that some sort of large landslide event – either a very large slide, or many smaller ones, or even both of those at the same time – has occurred in this catchment.  It would be very interesting to know just what has occurred.