16 April 2010
I have today updated my monitoring site for the Hunza (Attabad) landslide. However, there are a number of key developments that are worth noting:
1. The rate of seepage has started to increase once again
The graph of seepage against time shows that seepage is increasing rapidly at the moment, albeit at rates that are still only a fraction of the inflow rate:
The key factor here is the development of a new seepage point on the dam face (seepage point 4), which is now producing about 85 litres per second of water. The location of the four seepage points are shown below (from Focus):
Seepage points 2 and 3 cause me little concern given their location. Points 1 and 4 are clearly the ones that probably represent seepage from the lake.
2. The date of overtopping remains unclear
The outgoing NDMA chair recently estimated that overtopping could occur on 17th April (i.e. tomorrow). This is highly unlikely. On the monitoring site I try to estimate the date of overtopping based on the reported rate of reduction of the freeboard. My current best estimate is mid-June. However, the lake length has not really been increasing recently as the upstream section is currently steep (see image below from the Pamir Times:
Once this steep section is overcome the rate of rise may decline. However, this may be offset by an increase in inflow as snowmelt develops.
3. Something strange is reported at Shishkat
Shishkat is near the head of the lake, probably best known for the location of the KKH bridge that has now been drowned (image from the Pamir Times):
Local people at Shiskat are reporting “underground blast-like sounds” in this area. Of course there is little information about what these “blasts” might be, or indeed the reliability of the reports. However, one possibility would be the development of slope instability on the banks of the lake. Given that one failure mechanism for the dam is a slide into the lake and a wave that then overtops the dam, this needs to be checked out with some urgency.