Fish Passage at Xayaburi Dam Tested

The below article from the Vientiane Times, the local English language rag in the Lao capital city, states that Xayaburi's fish passage is being tested. This means that the construction of the dam has moved forward very quickly and steadily since I visited last spring. The fish passage, considered state-of-the-art by the Lao government and useless by critics, is apparently from a cutting edge design firm from Britain.

Though the passage is being tested by the engineers, the scientists are probably still scratching their heads regarding what type of fish are even in this reach of the river. Since no extensive study has been undertaken to account for the fish population, there are so many unknowns. Let's hope that this passage allows for migration and safe movement of the aquatic species, despite the new dam on the river.

*Fish passage testing underway at Xayaboury dam*

Vientiane Times, 11 June 2014

Xayaboury Power Co Ltd is currently studying fish swimming ability to evaluate the effectiveness of a demonstration fish passage facility at the Xayaboury hydropower project in northern Laos.

Deputy Minister of Energy and Mines Mr Viraphonh Viravong visited the site on Monday, accompanied by officials and members of the media.

Engineering consultancy firm Poyry Energy was hired to work on the project. Poyry Energy then contracted Fishtek Consulting to evaluate whether Mekong fish would be able to use a fish pass at the run-of-river Xayaboury hydropower dam.

Fishtek is a specialised international fishery consultancy based in Devon, UK. They are a leading British consultancy in evaluating the interaction between hydropower projects and fish.

Fishtek Consulting' technical director Mr Tobias Coe said the fish pass design was based on the best practice principles of taking the swimming abilities of fish into consideration when designing fish pass systems, tailoring them to specific species.

“What that means is we are not taking generic principles of fish pass design . . . this fish pass will be designed for the species that are present in the river Mekong,” Mr Coe said.

He said different tests were underway in the stream looking into the behaviour of the key fish species at different water velocities and how they react to obstructions, as well as the pure physiology of the fish and their swimming capabilities.

In response to concerns raised by Mekong Commission Committee stakeholders and experts, the initial design of the Xayaboury scheme was modified to incorporate sustainable solutions for local Mekong fish populations to pass through the hydropower dam.

One approach is a land-based “fish ladder” that goes around the barrage at an appropriate gradient or slope.

Fish swimming ability tests began in May this year and are ongoing. They will allow scientists to understand the behaviour of fish species and allow for the optimum design of the structures to allow all key fish species to pass through the hydropower dam.

The current fish pass design proposes four vertical slots of different sizes controlling the water flow between pools 20 metres wide and 8 metres long. Fish have to burst-swim through the slots before traveling the pool upstream to the next set of slots.

An experimental facility with a 24 metres long flume has been built at the construction site to investigate the specific swimming abilities of different species of fish.

Three different experimental techniques are being applied to ‘lead' species including Pa Pak Ta Leuang (Hypsibarbus Pierrei), Pa Tep (Paralaubuca Typus), Pa Dok Ngieu (Cycloheilichthys Repasson), Pa Nyon Nuat (Clupisoma Sinense), Pa Soi Hua Po (Henicorhynchus Siamensis) and Pa Nyon Thong Kom (Pseudolais Pleurotaenia).

The tests being performed include the velocity barrier test, the burst swimming test and the ‘umax' method. Tests will be completed in the next few weeks and conclusions about the design will then be made.

Interim conclusions confirm that a design velocity of about 1.2 metres per second can be used in the main slots of the fish pass. At this speed most of the fish species require several attempts to enter the flume during the velocity barrier tests. Construction of the US$3.5-billion 1,285 MW Xayaboury hydropower plant began at the end of 2012 and is now 30 percent complete.

Commercial operation is slated to begin in 2019. The dam's operational phase covers 29 years of the concession agreement from 2019 to 2048, before ownership is transferred to the Lao government.