Mega First: Dam safety risks to remain low

By NG MIN SHEN

Mega First Corp Bhd, which is involved in building the Don Sahong hydropower project in Laos, said present and future dam safety risks surrounding the project are expected to remain low, following the collapse of another under-construction dam in Laos on Monday.

In a statement yesterday, the group said it had received queries from various stakeholders on the risks of a similar situation happening to the Don Sahong project and the implications that might ensue.

“The board of the company has made the necessary enquiries with the management of Don Sahong Power Co Ltd and the project consultants.

“Having reviewed the circumstances surrounding the incident, and the specific and unique characteristics of the Don Sahong project, the board is satisfied that present and future dam safety risks remain low and are being (and will continue to be) appropriately monitored and managed, in accordance with the industry and international best practices,” the statement read.

“Saddle Dam D”, a subsidiary dam which forms part of the Xe-Pian Xe-Namnoy (XPXN) hydroelectric power plant in Attapeu, Laos, was found to have fractures on Sunday before its collapse on Monday.

At least 20 people were reported dead and over 100 are missing, while more than 6,600 people have been made homeless, after the dam’s collapse resulted in flash floods in six villages.

“At this juncture, the board concurs with the management of Don Sahong Power Co and its consultants that the incident is unlikely to result in any delay in the completion of the project or a material change in the overall cost of the project,” Mega First said.

In a statement to the board of directors of Mega First, Don Sahong Power director Khoo Teng Keat said there are several key differences between the Don Sahong project and the XPXN scheme, in the type and arrangement of structures and construction materials that result in a “significantly different and much lower dam safety risk profile for Don Sahong Power than normal”.

He said XPXN is a storage scheme which relies on being able to store very large volumes of water for generation during the dry season, whereas Don Sahong is a “run of river” scheme which holds about 1% of the total volume of the XPXN main reservoir. Moreover, he said the Don Sahong dam is a concrete gravity dam whereas the XPXN saddle dam is an earth fill embankment, which is permeable and cannot safely sustain overtopping.

He added that the Don Sahong scheme is located on one of many natural river channels and the associated natural river hydraulics combined to provide a higher than normal degree of dam safety and risk mitigation during extreme weather or flood events.

Construction of the project is ongoing and currently 65% complete, with filling of the head-pond with water from the Mekong River scheduled for the next wet season in 2019.

The two key dam structures in operations at the moment are the upstream and down- stream cofferdams or temporary dams, which are constructed at the inlet and outlet respectively of the 5km-long Hou Sahong channel, in order to keep the entire project work site dry throughout the construction period.

“The present status of the permanent dam construction is that the head-pond embankments that will form the permanent dam structures are substantially complete. These embankments are built from roller compacted concrete and conventional vibrated concrete — not from earth fill, and are thus of safe and robust construction,” Khoo said.

He said there are no communities or public infrastructure within the area bounded by the upstream and down-stream cofferdams and the as-built embankments, while in the event of a breach or overtopping incident, incoming flows would be confined to and contained in the area within the cofferdams and the as-built embankments.

The Don Sahong project is a run-of-river hydroelectric power scheme located at the southern end of the Sahong channel, one of seven major channels of the Mekong River, with a generation capacity of 260MW.