26 May 2010

Attabad: update report for 26th May

Posted by Dave Petley

The combined monitoring effort appears now to be providing consistent measurements of the remaining freeboard, and these are now being used in the media, which is helpful.  As of late last night the reported freeboard was 8.8 feet, which is 2.56 metres.  This provides a freeboard – time graph that looks like this:

This suggests that we are still on course for overtopping on about 27th or 28th May, although clearly this remains a moving target for all the reasons previously outlined.

Meanwhile, the media in Pakistan have now picked up on the inconsistencies in the measurements reported by NDMA, and in particular their incorrect measurements of freeboard.  This article is strongly critical of the error by the government agencies:

“However, during a tour of the dam site on Monday the NDMA chairman, Nadeem Ahmed, discovered significant differences in measurements recorded by the Frontier Works Organisation (FWO) and the Gilgit-Baltistan region’s public works department.  “He was furious when he noticed the discrepancies and realised the NDMA had been reporting inaccurate data,” a participating official said.  Mr Ahmed immediately ordered a dam-site demonstration of the methods used by the two government agencies, before declaring that the public works department’s “freeboard auto-level gauge” system, based on instrumentation manufactured by Nikon of Japan, should in future be the sole official data source

Again the question has to be asked as to why NDMA did not use the expert advice that was freely offered?  This decision continues to mystify me.

The state of the spillway is also a concern now within Pakistan.  From the same article:

The engineers said the 25-metre-deep spillway was too narrow to accommodate outflows of more than 2,400 cusecs from the lake, which held an estimated 1.2 million cusecs on May 17. A cusec is a unit of water flow equal to one cubit foot per second. “There is a serious possibility that the entry of water into the spillway could trigger a collapse of debris that would block it altogether,” an engineer said.

Several people have asked why the slopes on the sides of the spillway are failing given that the weather is dry.  The answer I think lies in the material – which dries on the surface but remains wet and very weak just below – and the loading from the excavated materials on the slopes above the spillway:

Finally, the Pamir Times have published a photo of the dam from the upstream side.  The watermark is a shame (but understandable).  What is notable here is that the upstream face of the dam has undergone a slope failure (the scar is quite obvious on the left side above the lake).  This does not threaten the integrity of the dam in any way, but does indicate that the materials from which is it formed are comparatively weak.

I’ll try to provide another update later, but have to travel to London to attend the launch of the UCL Institute for Risk and Disaster Reduction this evening.