20 May 2010
In the absence of any other information on the state of play at Attabad, I have plotted up the daily updates on freeboard from NDMA. The reliability of these is somewhat unclear as there are often contradictions between the indicated water level rise and the daily difference between freeboard measurements. There are also sometimes errors – e.g. the data for 19th May suggests that freeboard increased rather than declined overnight, but I have corrected that. So the graph for the last 19 days or so looks like this (the last datapoint is for 19th May at 18:00 local time):
Over the last four days the water level has risen at an average of 1.1 m per day, which means that the remaining freeboard should be lost in 3 or 4 days from 19th May, even allowing for the apparent slight reduction in rate in the last couple of days. On this basis, overtopping might be expected tomorrow (22nd May) or on Saturday 23rd May, but it may happen earlier.
Of course all of this is dependent upon the NDMA values being correct, but for the last two weeks the Focus and NDMA freeboard figures have effectively been the same. This does also mean that some of the media reported values of lake rise due to the GLOF earlier in the week were wildly incorrect.