By Shalika Wimalasena | Translated By Akitha Wijayasinghe
Geologists warn that the removal of the seismographs and seismometers in the dams which are located around the central highlands and lack of attention towards the identification of earthquakes could pose consequential problems in near future.
They point out that there are no mounted seismometers in any of the reservoir dams in Sri Lanka at present. Geologists further emphasized when constructing large reservoirs, it’s a must to install seismometers and the best example is the installation of seismometers in large numbers around the reservoir dams in India.
The Victorian risk
Two earthquakes have taken place within the past two weeks in the area around the Victoria Dam which is located in the central highlands. The seismometers in Pallekele confirms that these two incidents have taken place on 29th August around 8.00pm and 2nd of September at around 7.00am. These earthquakes have occurred in Haragama which is in a proximity of 3km to the Victoria Dam.
Ideology of the Geologists
One of the most known Geologists in Sri Lanka, late Professor. P.W. Withanage’s house is also located near Haragama. He had joined with the Mahaweli Movement as a geology consultant. Professor Withanage has proposed many ideologies regarding the construction of large reservoirs in the central highlands.
His theories regarding the geological cracks near the Victoria reservoir and the dam to be built on those cracks are considered significant among them. He has stated that due to these cracks, the mother rock breaks in to blocks and when during rainy season the water pressure on the blocks maximizes enabling them to move down and during droughts or dry season, the blocks slides up due to lack of pressure. This phenomenon can cause earthquakes which affects the stability of the reservoir. Geologists call the earthquakes that occur due to this phenomenon as induction earthquakes.
Due to this fact, the reservoirs which were built in central highlands including Victoria, Randenigala, Kotmale were fitted with seismometers to observe and monitor the effect of earthquakes on the dams. After few years after the installation, these seismometers have been dismounted providing several reasons.
Geologists signifies the fact that there are many large-scale reservoirs which were destroyed due to these induction earthquakes.
In north India, water reservoirs are installed with a large no. of seismometers. In Sri Lanka, seismometers are fitted in Mahakanadarawa, Buddangala & Hakmana areas. The seismometer in Pallekale collects data on earthquakes within the island.
From August to December, the water level of the Victoria reservoir decreases rapidly, causing a reduction in the water pressure on rock/soil blocks. Geologists suggests that this may cause at least slight movements of blocks causing minor earthquakes.