behind the headlines

Problems with fish ladders, dams and locks

Sunday, December 19, 2010 · Category Environment · comments 0


In 1995 the Japanese Government finished work on closing the Nagara River mouth, situated at a couple of hundred miles west of Tokio, with a dam including locks. The Dam is intended as a means to stop flooding and salinisation. In 2007 the Japanese organized a conference to ask for political attention for the negative effects of damming rivers.

The Japanese Nagara Dam and the Dutch "Haringvlietsluizen"

The problem between the two dams is surprisingly similar. The Japanese constructed the dam and locks including three fish passages or special fish ladders to allow wild fish returning from the salty sea to the sweet water river. In reality only 10 to 20% of the fish are able to take this barrier up the river. It's the same reason the fish ladders in the Dutch "Haringvlietsluizen" aren't working well either. The transition between salt and fresh water is to abrupt. The migrating fish simply have insufficient time to make the transition form salt to fresh water and adapt to the new circumstances.

Cultural differences between Japan and the Netherlands

Searching for solutions is quit different between the two countries. Japanese engineers have a high standing in society and Japanese are used to look for solutions in technology and concrete. Japanese try to influence politics, because it's there in the hierarchy were the decision has to be made and once it's made, they tend to move swiftly in execution.

Whereas the Dutch have more of a consultative culture. They tend to cooperate with a range of organisations in the region to find common ground and widely supported solutions. This is also the reason why just searching for the phrase "opening of haringvlietsluizen" delivers more than 20.000 reports, opinions and consultancy advices.

The Nagara river dam problems investigated

Some of the problems that have been investigated around the Nagara River Dam and locks.

1. Destruction of sea mingled with fresh water area (the down stream of the dam)

  • The high salt density of the sole layer
  • Low oxygen of the sole layer
  • A countercurrent of the sole layer

2. Turning into lakes and marches (the upper reaches of the dam)

  • No oxygen state of the bottom of a lake in summer
  • Abnormal outbreak of alga
  • Increase of midges ¬Āichironomus midges hardly inhabited at 6-10 km than river mouth for salt water going up.
  • Sedimentation of sludge.
  • Regression of the reed-field.

3. Interference of going up of wandering fishes

  • An interference with descent of sweetfishes immediately after birth to sea
  • A poor catch of sweetfishes and Oncorhynchus masou 
  • Crushing influence of Japanese common eel fishing

4. Influences to Ibi River

Ibi River and Nagara is next to each other by a dike. The branching bay of the latter was stopped in a dam, but the former is not. On this account, the tide gets into Ibi River like a brick.

Related articles: Salmon

Picture gallery

Nagara river pictures courtesy of Andrew Campbell

  • nagara-river-views.jpg
  • nagara-river-views-2.jpg
  • nagara-river-views-3.jpg


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