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Vientiane Times

Publication Date : 06-02-2013

One of the international engineering firms advising the Lao government on the Xayaboury Hydropower Project said the recent redesign will address the most pressing concerns of environmentalists and Mekong River Commission (MRC) member countries.

“This project is, from an engineering point of view, one of the most advanced of its kind, incorporating all the best information and the best available systems to make the project as good as possible and mitigate all the adverse effects,” Poyry senior engineer Knut Sierotzki said in an interview on Monday.

The government retained Poyry as an independent consultant to redesign the US$3.5 billion dam project in 2011, in light of concerns expressed by MRC member countries about possible impacts of the mega-development project, the first run-of-the-river dam in the lower Mekong mainstream.

The dam redesign was undertaken to ensure that the construction of the hydropower project in Xayaboury province meets the Lao government's obligations, including the 1995 Mekong Agreement, and conforms to MRC design guidelines and best international practices.

Sierotzki, who is also director of Hydropower Asia and Russia for Poyry Energy, said that environmentalists and MRC member countries have expressed valid concerns regarding fish migration and sediment flows downstream.

Fish is major source of food for Mekong riparian countries while sediment flows are vital to aquatic life and as fertiliser for crop cultivation.

Typically the design of a dam involves a single system to aid upstream and downstream fish migration. But in response to concerns about the Xayaboury project, Poyry engineers have come up with three innovative fish passage facilities.

According to Sierotzki, the navigation lock that enables boats to pass the dam will also serve as a fish-lift system. Fish can be attracted into the lock system and then transported upstream, he said.

The second system is a conventional fish ladder. As part of the redesign, this fish passage facility has been extended from the original 500 metres to more than 2 km in length, to ensure effective migration.

The third system is a fish-lift to carry fish that are not strong enough to use the conventional fish ladder.

“These concepts are globally tested in various locations. In order to make them specifically adapted to the Mekong, we have chosen not to select one system but to select all three systems,” Sierotzki said.

Another of the major design changes is to equip the dam with a sediment flushing system that will be able to release more sediment during the rainy season.

“The first concept, which was normal for run-of-the-river power plants, was to fill part of the reservoir to reach a new equilibrium and then start flushing sediments. That would have taken a few years.

Now instead, the new system will be able to flush sediments from the first year onwards. We will not have large accumulation of sediments in the reservoir,” he said.

Unlike dams with higher walls, run-of-the-river dams do not create a large permanent reservoir. Rather, this reservoir consists of only the daily flow of river water, which is utilised for power generation.

Scientists working on the Xayaboury project have been conducting major studies including fish-counting using sonar devices and an investigation of sediment flows up and down the river.

The data collected from these and other studies will be employed to further refine the dam operations and help mitigate fish migration and sediment flow issues, Sierotzki said.