Fish-friendly irrigation

January 26, 2022

Southeast Asian countries, including those in the Lower Mekong region, are experiencing a boom in irrigation development as agricultural modernization programs are being rolled out.

However, irrigation infrastructure creates new barriers to fish migration, interfering with spawning and feeding patterns. These impacts have been little considered, compared with the international attention that has focused on the impacts of large hydropower dams.

A fisheries project that began in Lao PDR has sought to tackle exactly this problem, and is now working in Cambodia, Myanmar, Thailand, Viet Nam and Indonesia. The research outcome, ‘Achieving fish passage outcomes at irrigation infrastructure: a case study from the Lower Mekong Basin’,[1] is now published in the March 2021 issue of Aquaculture and Fisheries. The paper explains the process the project team went through to plan, consult, and co-design an effective fishway.

The fishway was designed to suit medium and small fish that were previously blocked by an irrigation dam at the Pak Peung wetlands near Vientiane. The fishway still operates as a demonstration site for those wanting to learn about this technology.

The researchers highlight several important principles, including:

  • consulting with local irrigation bodies and villages to ensure that the design and operation of the fish passages suit local conditions and preferences;
  • considering specific local features of fish species, such as maximum and minimum sizes, and their migration behavior, so that a suitable design can be adopted or developed;
  • understanding the specific local features of river hydrology over the annual river cycle—important, as river levels in the Mekong basin can vary hugely; and
  • ensuring that design features enable fish to locate the fish pass entrance, and that the exits include resting zones for tired fish, so that they do not get swept back downstream.

Their paper gives special attention to the challenges of establishing fish-friendly infrastructure in developing countries, where design and construction may be carried out by a foreign company or aid project.

Better infrastructure

The authors note that fishways at large hydropower dams have not always been successful, in part due to fish mortalities from high spillways and hydropower turbines. In comparison, irrigation structures are much lower and pose fewer risks.

Their experience highlights the importance of working closely with government and residents at the fishway site to ensure the design meets local needs and conditions. This project, at the Pak Peung wetlands near Vientiane, went through significant design changes, based on feedback from local villages that the original design posed an unacceptable drowning risk to children.

Children play fearlessly at the irrigation dam site. The fishway design was modified to have cone-shaped passages and shallower channels, so as to reduce drowning risk.

The authors also worked closely with local operators to ensure that the fishway performed as expected, and that maintenance or operating issues were addressed. In the case of this project, supported by the Australian Centre for International Agricultural Research, cameras were installed that would email a daily photo to the team in Australia.

Future food

Based on typical costs, the research team estimates that installing fish passages in irrigation infrastructure will likely return a value greater than the cost of each project in just five years.

Irrigation modernization programs, the authors argue, are a once-in-a-lifetime opportunity to ensure that local communities get to benefit from functioning fishways.

Acting now will ensure development that is meant to increase food production does not inadvertently destroy the existing fisheries food source.

Read the full paper here:

[1] Lee J. Baumgartner, Chris Barlow, Martin Mallen-Cooper, Craig Boys, Tim Marsden, Garry Thorncraft, Oudom Phonekhampheng, Douangkham Singhanouvong, William Rice, Michael Roy, Lin Crase, and Bethany Cooper.

Achieving fish passage outcomes at irrigation infrastructure; a case study from the Lower Mekong Basin, Aquaculture and Fisheries, Vol. 6, Issue 2, 2021, pp 113-124.

ISSN 2468-550X

Photo credits: Charles Sturt University and the Australian Centre for International Agricultural Research

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