Design for the benefit of non-human inhabitants: The salmon ladder

Wherever humans settle and human habitats expand into the surrounding landscape there will be an inevitable confrontation with the members of encountered ecosystems. More often than not, these confrontations ends in the prevalence of the human habitat, on the expense of the wildlife. These interferences might cause the separation of wildlife populations or prevent the natural migration of certain species. If the design of cities, villages, bridges, dams, roads ect. got us into this mess, can design be deployed to get us out of it?

In the next four blog posts I will be doing a case- study of a type of wildlife corridor – a wildlife corridor being a construction or design that facilitates a connection between habitats that have been separated by human action- that has been intentionally designed to aid the migration of fish in obstructed water streams. The salmon ladder.

Urban surfing on the man-made river Eisbach in Munich (photo: Malin Eriksen)

According to Wikipedia there are written reports of early use of bundles of branches for the easing of passage for fish in France, dating back to the 17^th century. However, the fish ladder was first patented by the Canadian, Richard McFarland in 1837. McFarland was the owner of a water-powered lumber-mill in New Brunswick in Canada. He designed a pass way so that the fish could bypass the dam that was created for the benefit of the lumber-mill.(https://en.wikipedia.org/wiki/Fish_ladder)

Today the use of fish ladder (or salmon ladder) is quite common, especially in areas where natural rivers have been dammed or where the natural passage of the water is obstructed in other ways. The general principle of the salmon ladder is to create a passage that allows the fish to migrate up the river that does not obstruct with the fry’s way down into the ocean. Some fish ladders in areas with especially rough waters also incorporate areas with slower moving water where the fish can rest between hurdles. The clue is that anadromous fish, like salmon and the steel-head trout is attracted to the counter current in the river and will naturally swim up against it. The velocity of the current in the fish ladder therefore has to be big enough to attract the fish, but small enough to not exhaust or force the fish back down the stream.

As mentioned, there are several ways of designing a fish ladder with different technologies applied. In the next three blog posts I will be looking at the Vertical-slot pass. This is the type of salmon ladder that is built in Akerselva in Oslo.

The fact that I live in a city, a Scandinavian capital that is the proud owner of a salmon ladder, makes me curious as to investigate this further from a design perspective. So this is it, the start of my investigation into the urban salmon ladder.