The Xayaburi project is the first one to be built on the Lower Mekong and therefore it was particularly difficult to design the fishpassing facilities since no direct reference and only very little data were available in the initial design phase.
In the beginning the project was required to carry out additional fish studies and re-design large parts of the fishpass structures.
The studies carried out addressed questions of species, biomass and fish swimming abilities.
The design improvements comprised the following:
1) Downstream migration: the facilities were improved in order to be operational all year round instead of only during the flood season. This required an increase in size of the affected galleries and the project also introduced a pump station in order to minimize losses in energy production during the low flow season. The exit channel was improved by hydraulic modelling to provide optimal flow conditions for the fish.
2) Upstream migration: The original concept of a fishladder spanning the total height of the dam was replaced by a combined system of a fishladder and a vertical lock system. The nature of the fish ladder was changed from a single slot ladder to a hybrid multislot ladder; also the dimensions of the ladder were increased substantially due to the expected biomass and to provide acceptable energy levels in the pools.
Upstream fishpassing commenced in early 2015 through the Navigation Lock. The lock is equipped with specific water feed systems allowing upstream fish migration through the construction period.
The construction of the permanent fishpassing facilities, both for up- and downstream migration are substantially complete. Both systems will commence operation by the end of 2018 when the reservoir is impounded to the full height and the relevant systems have been finalized and commissioned.