Laos is building the first run-of-river hydropower dam on the Mekong River downstream from the storage cascade in China. With construction nearly one-fifth complete, the Vientiane Times visited the site to find out how the project is progressing.

Xayaboury province, Laos : The giant river Mekong was a muddy brown and at its highest level on August 15 when a group of visitors, including local and foreign journalists, arrived at the Xayaboury project site at midday.

Being at the dam site felt like standing in the bottom of an empty pool 40 metres deep. Instead of water, the surface below the coffer dams cradled a sun-drenched construction zone filled with cranes, dump trucks, cement, steel bars and thousands of workers in colour-coded hard hats and safety vests.

When completed in 2019, the dam will have an installed capacity of 1,285 megawatts, and 95 percent of the electricity produced will be exported to Thailand. This US$3.5 billion hydropower project is a “transparent” run-of-river dam which, according to the developer, the Xayaboury Power Company Limited (XPCL), means “nothing is added, nothing taken from the water”.

But international environmental non-government organisations warn that the dam could block fish migration which may affect 60 million people said to be dependent on the Mekong River for the protein in their diet. Critics say more studies are needed to gain a comprehensive overview of the downstream impacts.

Engineers on site explain that a number of investigations are underway to address concerns about fish migration. “We have determined with these studies what the detailed requirements of the different fish species are to be able to move upstream and downstream in their natural migration cycles,” said the director for hydropower in Asia and Russia of Pöyry Energy Ltd., Mr Knut Sierotzki.

While visitors took photos of the dam from the hilltop, he showed this correspondent around the dam site and pointed to some of the special features under construction – the navigation lock, spillway gates, powerhouse and fish ladder.

To study the number of fish and the various species that pass through the river, a hydro-acoustic camera is being used to capture ultrasound images underwater every six hours over an entire cross-section of the Mekong. This has been going on since the beginning of 2012, said XPCL lead engineer Mr Prat Nantasen.

With only one piece of equipment, they have to move the camera continually in four sections between the riverbanks. Data from the camera, with its scope of 30 metres and 30-degree angle, are collected every month. Mr Prat has yet to summarise the data for the last month. He said120 fish species caught by net also are being studied to determine their age and rep roductive stage.

In the revised dam design, XPCL will use three different systems of fish passage facilities – an elongated fish ladder, a central fish lift and the navigation/fish lock system.

In addition, fish friendly turbines are currently being tested. Such turbine types, which have already proven their effectiveness, for example, in the Tennessee Valley in the United States, will be used in the Xayaboury dam, said Mr Sierotzki.

Mr Charlee Srivichit, engineer and advisor from Southeast Asia Energy Ltd (SEAN), told reporters the Xayaboury dam fish ladder was originally designed to be about 1.8 kilometres long. Based on recommendations made by Pöyry, the fish passage design has been changed to cater to the requirements of various species in the Mekong. The design is now being modified further by Swiss company AF Cole nco to make it much flatter.

Some fish passages in older dams were found to be less effective than planned, Mr Sierotzki said. But knowledge in this field has moved forward and XPCL is adapting the best passage systems found in different river types and geographical zones. He added that if some fish species were not fully accepting the fish passage, XPCL would be able to adapt or extend the fish transfer systems. “T hat’s what I call a flexible design,” he stressed.

Environmental experts are not convinced that the design will enable nutrient-rich sediments to pass through.

“Sediment is a complex subject to understand,” Technical Advisor for Sustainable Hydropower and River Basin Management of the WWF Greater Mekong Programme, Dr Victor Cowling, told Vientiane Times earlier.

He pointed out that when the sediment is being flushed through, power cannot be generated, and there is a strong risk of major problems directly downstream of the dam resulting from too much sediment being released in too short a time.

France’s Compagnie Nationale du Rhône (CNR) is carrying out an extended sediment sampling campaign which it has been doing over the last 12 months along a 1,000 km stretch of the river, hoping to understand the detailed sediment processes and especially the transportation mechanics of the coarser sediment particles.

At the dam site, the SEAN engineering advisor pointed to the drawing of the spillway gate on an XPCL brochure, then looked up, stretched his arm, and pointed out the foundation of the spillway gate that will control the release of water downstream. “Sediment will be flushed once a week in the rainy season and once or twice a month in the dry season, or a total of at least 20 times a year.”

Every month the amount of sediment will be checked in the river bed, on the surface and at the mid-level of the water, he added.

Aiming to be a significant hydropower exporter in Southeast Asia, the Lao government has a long-term plan to build eight more dams in the lower Mekong River.

Deputy Minister of Energy and Mines Mr Viraphonh Viravong, who joined the site visit, was asked by a journalist if he was certain the river would stay healthy. “Sure. One hundred percent,” he said. “This is our life. We are not talking about ourselves only. We’re talking about our children, our generations to come.”

Lorie Ann Cascaro of MindaNews is one of the fellows of the FK Norway (Fredskorpset) exchange programme. She’s currently in Laos and hosted by the Vientiane Times.

Source: Vientiane Times
Published on August 26, 2013