26 June 2010

Attabad – situation as of 25th June,

Posted by Dave Petley

NB I have updated this post, and changed the title.

Apologies for the lack of posts over the last few days – I have been in a meeting in Bermuda that has left little time to tend to this blog.  Meanwhile, although small scale blasting of the spillway has reportedly continued, as of yesterday the lake level at Attabad is continued to rise by 10 to 20 cm per day, with the effect of both further drowning houses, hotels and roads upstream, and increasing the volume of water in the lake.  Unfortunately I do not have any information about the blasting, or any pictures, but my analysis of the flow of the data is that the short term lake level graph now looks like this (correct to yesterday morning)

The lake level is now about 5.5 metres above the overtopping level, and at the moment there is little sign that this is reducing.  Thus, the long term lake level graph now looks like this:

Meanwhile, spillway discharge has  increased, driven primarily by a substantial rise in inflow:

I am intrigued to know whether this increased discharge has started to drive a new wave of erosion downstream.  Finally, this graph compares inflow and spillway flow over the last ten days or so:

It is clear that at the moment inflow and outflow are directly linked – i.e. that the increase in spillway flow is due at least in part to increasing inflow.  The grey line represents the point at which spillway flow equals inflow – i.e. the point at which the lake volume should stop increasing.  This does not account for seepage, but as this is now a tiny fraction of spillway flow this is not a major problem.  It is clear that recent increases in inflow were not being balanced by increasing outflow.

It should be expected that the inflow will continue to rise over the next few weeks, so this graph will be interesting to observe.  Hopefully the spillway operations will start to increase the outflow in a controlled manner in the next few days, such that the lake level starts to fall.