This suggests that we are still seeing an incremental increase in flow. However, interestingly, the rate of inflow and the rate of outflow now appear to be balanced, such that the lake level should stop rising (for a while anyway). If this happens, and spillway flow continues to increase, we will know that erosion is developing.
Dave- There could be some base level where the rocks/boulders will hold. If this is the case, then an increase in flow beyond the inflow would only be a result of an increasing of the spillway width. In other words, let's consider the ultimate lake depth/dam height. (This is a bit touchy to discuss, as geological time is too long, but nanoseconds are far too short. If we can get outside of imminent failure, but even this is a bit touchy, as even engineered dams have been known to fail, how high will the dam be?)
ReplyDeleteAssuming the dam holds, even if the best engineering reports suggested that the risk of immediate failure was low, I am not sure that I'd be comfortable living downstream...
Best wishes on your new living conditions.
Dave, there was a report yesterday in Pamir Times that the inflow into the lake had increased to about 4500 cusecs (128cumecs). There was also a report that the rise of water level in the lake yesterday was about 8 inches (200mm) compared to the 24 inches (600mm) previously. This would suggest that yesterdays outflow was about two-thirds of the inflow. Yesterdays figure from your graph of around 80 cumecs for the outflow would therefore suggest an inflow of around 120 cumecs. This ties in well with the 'measured' inflow.
ReplyDeleteIf these figures are right, todays ouflow of 105 cumecs nearly matches inflow. If downcutting does not increase, then quasi-steady state conditions could soon prevail. On the otherhand, downcutting could continue resulting in increased outflow and further erosion ...
Pamir Times indicates that at 4am this morning local time, the water level at Gulmit (part way up the lake) had stopped rising. This indicates that outflow now matches inflow. It will be interesting to see whether over the next day or so the lake level starts falling indicating that downcutting or widening of the spillway channel is occurring. Downcutting could still lead to a breach, but widening of the channel is unlikely to.
ReplyDeleteThe early part of the discharge graph is consistent with increasing flow through a stable channel/weir as the water level rises, but if the water level has now stopped rising, then the later part is not. This is perhaps not surprising, but the latest measurements indicate either widening or deepening of the channel consistent with the photographs.
ReplyDeleteShould we be worried about the possible impacts of Tropical Cyclone Phet?
ReplyDeleteDave.. you're driving us crazy with the lack of updates. I know steady-state seems to have been reached but it would be nice to have updates on the dam that are not 2 or 3 days old!
ReplyDeleteIvan - don't be so rude! Dave does this blog in his spare time. He has a fulltime job as a professor and, as you no doubt read in an earlier post, he moved house earlier this week. It's not surprisng he hasn't had time to update. Don't hassle him. And maybe there's no news to report anyhow, or he hasn't been able to get hold of any.
ReplyDeleteI am not a geologist but been a mountaineer and trekker. I have two questions for men of knowledge.
ReplyDelete1. Why could the FWO not widen the spillway. Was it a time or resource constraint or sheer negligence?
2. We know that the rocks in the area are geologically young and the land sliding phenomena began in 2002. Did the geologists, FOCUS and the Government carry out any studies then.
3. Some boulders seem to hold thereby blocking flow and erosion. Would controlled blasting be feasible?
4. In an area such as this is Basha Dam a figment of imagination or practical?
I suspect Dave may not have internet access set up at his new home yet and will need to wait until he gets to University in the morning before he can update us with the situation. Alternatively he may be away for the weekend!
ReplyDeleteThe Pamir Times reference indicates that outflow marginally exceeds inflow and that there is evidence that the lake level is falling. It is not clear the period over which the fall of 1.5 inches (40mm) occurred, but assuming this is from the maximum lake level, this would indicate that the outflow is about 5% greater than the inflow. This tallies with the quoted figures.
ReplyDeleteAssuming this figure is correct, it would seem that little downcutting of the spillway is occurring and that the increase in the outflow is probably a result of the widening of the channel. On this basis, it now seems that the potential for a sudden breach of the "dam" is reducing at least until the inflow into the lake increases.
FWO (Frontiers Works Organisation) an Army Engineers branch should be quite capable of opening up the stuck narrow mouth of the barrier which should not be a problem for them, If surface explosive charges are feared that they may trigger the landslides. Deep charge may be tried to ease up the barrier and make a way for drainage.
ReplyDeleteWithout breaking out the fluid flow differential equations, I am not sure that if we held the dam height constant that a lowering of the lake height would not be possible. I am sure that if the inflow exceeds the outflow, then the lake will increase in height. Similarly, if the outflow exceeds the inflow, then the lake height will decrease. That's the easy part.
ReplyDeleteWhat I am not so sure about is the claim that erosion is the only way to lower the lake height. Here is why. If we keep the dam height constant, there is a possibility that the lake height could go lower.
Here is one example:
Let's start with the inflow and outflow equal, so the lake height remains constant. Now, without any erosion, the inflow drops (the ultimate example would be if there was a landslide at right where the river spilled into the lake, thus cutting off all flow into the lake). The outflow, through that small spillway, would initially be flowing the same amount (as the lake height has not initially changed), but since the depth of water over the spillway is greater than zero (a differential, in this case), the water would continue to flow (again without any change in the dam height). In this situation the lake level decreases without erosion.
Thus I am going to suggest to be careful when claiming that changes in the lake height is a result of erosion of the dam, since there are cases where the lake height can change without erosion.
A significant drop (however much that might be) in lake height, however, would probably indicate something more.
Having seen the Hunza river in peak flow and the relatively small amount that is south of the block - is there any possibility that water is going somewhere else beside over the spillway. If it hasn't raised in height in 48 hours then it is not backing further up the Hunza river - confused by low flow
ReplyDeleteNow c'mon Dave, we're waiting, we are now addicted to your updates, give us some lowdown. Looks like you got too much obsessed with your new place.
ReplyDeletei think seepage will play an increasingly important role as time goes on. We could even reach a stage where pretty much all of the outflow is draining through the dam rather than over it. This should thus be treated as a groundwater flow problem, with various scenarios considered using MODFLOW.. what is very difficult to predict is exactly how the hydraulic conductivity of the mass can be assumed to change, both spatially in x,y,z and with time.
ReplyDelete