The underground water seepage that occurred in the main tunnel of Uma Oya hydro-power and irrigation project earlier this year has now been sealed and the total ingress has been reduced significantly, said Secretary to the Ministry of Mahaweli Development and Environment, Anura Dissanayake.
One of the biggest development and construction projects in Sri Lanka, Uma Oya aims to provide water for drinking, industry and irrigation in the southeastern dry zone of the South Asian island and generate much needed hydro-electric power.
The multi-million-dollar project consists of a hydro-electric power plant, three tunnels with a collective length of 23 km, and the Puhulpa and Dyraaba dams, which span the two main tributaries of the Uma Oya River.
Earlier this year, underground water seeped into a 15-km section of the tunnel connecting the Dayraaaba dam with the powerhouse. The issue grabbed headlines and fueled environmental concerns.
At the time of the incident, the Iranian contractor Farab moved quickly to address the problem, seeking advice from their existing international consultants including Poyry and Amberg from Switzerland and specialized grouting experts from Norway. According to Farab, new equipment and special material was applied to control the water ingress and seal the area.
“Farab has got on with the job with caution and certain precautions have been taken in order to avoid the risk of further water ingress and a resultant environmental impact,” Dissanayake said.
Farab said last week that the excavation of the tunnel was continuing at a slow rate to enable extensive drilling and injection of cement grout ahead of the tunnel to control ground water flow and improve stability of the rock formation.
“With the sealing completed and intensive ground water control implemented, we are confident that the remaining construction work will have no impacts on the surface,” the company said
Complex geology and Unforeseeable challenges
For more than a decade before the Uma Oya contract was signed, a number of pre-feasibility studies were conducted into the development of hydro-electric power and the transfer of excess water from Uma Oya River to the drier southern regions.
These studies, some carried out as early as 1991, were conducted by leading consultancies and engineering companies: Sri Lanka’s Central Engineering Consultancy Bureau (CECB); the Montreal-based engineering and construction firm SNC Lavalin Group Inc. and Germany’s Lahmeyer Group, a leading international engineering company.
After securing the contract , Farab spent a year conducting full-blown feasibility studies before starting construction work. However, the complex geology of the area and the scale of the venture meant that not all underground hazards could be foreseen.
“With large-scale infrastructure projects like Uma Oya, there is the possibility of a water leakage happening at some point”, Dissanayake pointed out. “There is blasting and drilling in underground construction and water ingress can happen under the surface. It is inevitable.”
The secretary said even some massive projects in Sri Lanka have faced large water ingress during construction. There Samanalawewa hydro-electric project financed by Japan and Britain for example, has been subject to large leaks.
According to Sri Lankan officials, the Uma Oya project will spur development and play a key role in the growth of arid and under-privileged agricultural districts of southeastern Sri Lanka.
“The project’s benefits are immeasurable. In addition to adding 120 MW of hydro power to the national grid, the venture will provide much-needed water to the country’s southeastern dry zone,” said Dissanayake.
People who live in south eastern Sri Lanka are badly hurt by lack of rainfall. Most are dependent on agriculture for a living and do not have access to enough water to drink or water their crops.
According to the Ministry of Mahaweli Development and Environment, there are more than 30,000 hectares of agricultural land in the area that cannot be fully utilized due to water shortages and lack of irrigation facilities. However, through the Uma Oya project these lands can be fully utilized and another 5,000 hectares of new land can be cultivated.
The Sri Lankan government is also aiming to develop industry in the area after the completion of the project.