KARAKORAM Highway is an incredible feat of engineering. It passes through the rough terrains of Gilgit-Baltistan and presents a magnificent view of the beautiful landscape around to visitors and travellers. However, to meet the urgent need for its expansion, some mega engineering projects are being carried out. These works have caused serious damage to the geology of the area and disturbed its soil, making it vulnerable to landslides and other catastrophes.
Landslides are a regular feature in this part of the region but human intervention has accelerated its pace. A recent landslide has resulted in the creation of what is now Attabad Lake. This catastrophe has put the local population in dire straits and also badly affected the Pakistan-China trade which runs into millions of dollars. Not only the artificial lake is very harmful for our water reservoirs, it will accelerate the rate of sedimentation in them.
To be precise, the Attabad Lake is a result of natural calamity and, therefore, very different in function and structure compared to normal concrete dams.
Since it is a huge unplanned obstruction, its behaviour is different. This obstruction is composed of huge boulders (each one of which can weigh hundred of tonnes), stones and coarse soil. The erosive action of flowing water is different in this case. If the portion of soil is less in aggregate, then the rate of erosion will be less and vice versa.
One may note that that this obstruction is longer than the one sees in regular dams and therefore its chances to suddenly break are slim but it will start disintegrating slowly from the lower end. Generally, there are two clear situations for this lake — it will disintegrate quickly or slowly.
In case of immediate disintegration, definitely there will be a huge flood of water along with thousand tones of debris, which will devastate a large area downstream.
The height of this flood will be fairly lower than the level of water in the lake at that time. But this mishap can happen only when a huge portion or all of the length of the lake obstruction disintegrates from downstream in a short time. Or it can happen if the seepage of water increases drastically, which will weaken the base of the lake by making it hollow.
In the other case the lake can start disintegrating from downstream very slowly and water leaks out in a pretty safe manner through the spillway. There are two possibilities in this regard; either the spillway continuously gets enlarged by erosion and all the water flows out or there is a chance that the erosion rate in the spillway gets slow or even stops, and the outflow of water stops and spillway will then require manual excavation for safe disposal of water.
This can happen if the exposed bed of upstream portion of the spillway consists only of boulders or huge stones. These will not be eroded by water easily and quickly, and hence the spillway will gradually stop functioning. In such a condition manual excavation can be required for deepening of spillway for safe disposal of water. Presently, the outflow fluctuates in the range of 4000-5000 cusecs from past one week. If this situation persists for some days, immediate attention will be required for determining the condition of spillway bed.
Therefore, in this situation, one may conclude that continuous moderate erosion of the spillway in its depth and width is the safest possible condition for the safe disposal of water. Regarding the outflow of water, there are three stages
1- If the outflow is less than inflow, the level of water in the lake will increase.
2- If the outflow is equal to inflow, the water level will be steady.
3- If the outflow is more than inflow, the level of water will start falling and the lake will start emptying.
In the first stage, as the rising water level will exert immense pressure on the outlet, therefore the speed of water will be high and so will be its erosion. In the second stage water speed will be moderate and in the third case it will flow under the force of gravity.
Currently, the outflow seems to be in the second stage. In coming days more melted water from the glaciers will be added to it along with the rainwater. So, one can easily conclude that this stage might continue for a week or so with little fluctuations in outflow/inflow ratio.
Of prime importance is the third stage. In the current situation it can initiate after a considerable increase in the size of the spillway which will increase the outflow. Initial outflow at this stage can be 9000-10000 cusecs or even more and it may go up to 20000-25000 cusecs. If the spillway continuously gets enlarged the dam can be empty any time after mid-July.
Summer is of very short duration in this area. Therefore, a very important point arises that, what will happen if the lake remains intact for another two months? In this case the winter will play a very dangerous role. Water inside the obstruction and cracks will start freezing and expanding. Therefore, the whole structure can become very fragile. In this case anything worse can happen due to pressure of present water stored in the lake. So we should keep in mind that this summer is the best opportunity to get rid of this artificial lake safely.
It has also been learnt that the debris resulting from the landslide contains traces of limestone, which is a bonding material in the presence of moisture and pressure. These both conditions are present in the depth of the lake's obstruction. So a very scientific approach is required to get a clear picture in this regard.
In a nutshell, there is a need to continuously monitor the situation scientifically and to take proper steps immediately. Also getting advantage of this situation a brief technical study of all of its aspects should be carried out by research bodies so that we can get valuable information which will help us in future.
The disaster of Attabad is not a big surprise for any ecologist or environmentalist. The way we are treating our mother nature, these things are going to happen frequently in future and even in worse manner.
The need is therefore to understand these incidents logically and scientifically to not only avoid their recurrence but also to evolve a preventive strategy.
We have to take this incident seriously as it may be the beginning of a chain reaction in this tract because mega engineering activities being carried out for reconstructing KKH and other projects are causing serious damage to the geology of the area, making it vulnerable to landslides and other catastrophes.
The writer is associated with Pakistan Forest Institute, Peshawar.
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