What is the cost of installing a fish ladder on a wier?

Question

In france, particularly - to allow migrating species like salmon to swim upstream. Is it very expensive or difficult to do?

Answer 1

The costs depend on the channel slope, the height of the weir, width of the stream (if you want to span the channel), water velocity parameters, height of the steps, and the materials you want to use.

The cheapest design is probably a swimmable boulder cascade, which is nothing more than several layers of boulders irregularly placed below the weir to create multiple paths there the fish can work their way through the rocks. In the bottom layers, sands, clays and pebbles are packed in between the boulders to force the water to flow over the boulder instead of through them.

With weirs, the most common approach is to replace a single weir with several smaller weirs that have a lower jump height and suitable water depths and velocities over a wide range of flows. This is very easy and somewhat inexpensive to do with boulders and an excavator. The most expensive part of this type of approach is the engineering and surveying to make sure the elevations and distances are designed correctly. Instead of boulders, concrete can also be used, but designs using concrete are generally much more expensive and far more likely to function improperly.

Another approach is to add a ladder to an existing weir. This approach tends to need frequent maintenance to remove sticks and debris that get stuck in the ladders, and ladders are generally less effective than constructing a series of low weirs. However, ladders can be built very inexpensively by welding sheets of aluminum together to form a baffled chute that can be bolted to the weir.

Here's a couple of references you can download:

Answer 2

depends on the height of the weir and the flow of the water, but - if the salmon ladders that I have seen at Teesside park and Pitlochry in Scotland are good examples - then it will be the massive constructional exercise. Probably, well into 6 figures....

Answer 3

i dont know