So what are the options? As far as I can tell the possibilities are as follows:
1. Maintain the status quo until after the peak flood has passed.
One option is to do nothing except to monitor the lake. Given the apparent stability of the dam, this option has attractions, although of course it leaves the displaced population in a state of limbo. It is unclear as to how long the IDPs both upstream and downstream can continue to live in their current difficult state - the ongoing protest on the dam site suggests that things may be quite volatile now. In addition, the risk from the dam is undiminished, but with large numbers of people out of harm's way this is being managed.
2. Allow the population to return, protected by a warning system
A second option is to set up a full warning system and to allow the population on the downstream side to start to return to their land. There are risks associated with this of course - and these would need to be fully explained to the vulnerable people - but perhaps the local people would view those risks as being tolerable compared with the challenges of their current daily lives.
3. Widen the spillway further
NDMA could attempt to further widen the spillway, although it is now clear that widening operations to date have not caused a substantial drop in lake level. A wider spillway may increase the capacity to withstand the peak flood, and might avoid further rises in lake level.
4. Deepen the spillway
If the aim is to resolve the situation then it is necessary to deepen the spillway, presumably using explosives delivered via military hardware. This was the approach used at Tangjiashan to initiate the breach:
A similar approach was used elsewhere in the Wenshan earthquake area - for example this is the Shinangou landslide dam being demolished:
The size of the blasts needed to initiate a breach in China was very large, as the images show. Needless to say the use of explosives in this way carries very considerable risks - especially in an area as geologically unstable as Attabad - and therefore should only be undertaken with great care. The caution that NDMA are showing with this approach is well-advised. In my view such an approach may well be too risky, but I am sure that the authorities are weighing up the pros and cons fully.
Thus, at this stage the viable options remain really very limited indeed. The situation remains one of waiting to see what happens, frustrating though this is for the local people.
Options during the winter?
If the dam survives the summer floods then the flow rate will decrease substantially during the winter. This might be a time to start trying to induce a controlled lowering of the lake or to start to armour and protect the spillway. Perhaps siphons and pumps could be used to bring the lake level down to the point that it is possible to work on the spillway, which could then be deepened or engineered. This would require a substantial investment in time and money, but may well be viable. However, this is a long way off at the moment.
It would be a fun fantasy if I could be put in charge of some short range artillery and allowed to have a go at it; except for the fact that the consequences of my actions could endanger so many people. So I'll leave it to the experts (if there are any; there might not be), to actually decide.
ReplyDeleteBut if, in my fantasy world, they let me do stuff and no one lived downstream, I would take a surgical approach. Here's what I would do:
1. Take out that isolated boulder at the top (either by getting someone onto it to drill and blast it, by shooting it (with what?), or by blasting just below it to erode the material that is holding it up (how do that?). This should increase flow significantly.
2. With that boulder gone, the choke point should move upstream some, although my suspician is that there won't be anything that stands out as a juicy target. So if more was needed, I would continue to focus on the area about where the boulder is now to increase the slope, and gradually work back up the stream. The idea is that there is no sense blasting the bottom of the channel unless the force of the flow is sufficient to sweep the debris downstream.
But I'd be taking it in steps, and allowing the consequences of one step to reveal the best action for the next.
Winter inflows were in the order of 30 cumecs. Bearing in mind that seepage will continue to counter this, with a sustained effort it may be possible to pump a sufficient volume of water to allow works on a dry spillway. However, the effort required would be very large.
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