Initially, researchers at Luleå University of Technology performed pre-action modeling to ensure that placement of structures is made as efficient as possible in the demonstration sites. Below is a summary of some of the results from this study.
- If the aim is to increase the water depth upstream, the block should be placed in calm stretches. If the riparian zone is very flat this will result in larger water covered area and decreased water speed.
- If the aim is to reduce the current velocity downstream, the block should be placed in high areas with high current velocity.
Rock characteristics in order to create a large calm area (pool) upstream:
- If the current velocity is 1 m/s the rock should be larger than 0.5 m in diameter.
- If the current velocity is 0.5 m/s the rock should be larger than 1 m in diameter.
- Choose a rock with a ruff surface instead of smooth. It will stabilize the pool.
- If possible, choose rocks with a flat surface. The flat surface should then be placed downstream to create the largest pool possible.
To create a calm area between two rocks arranged in a staggered configuration:
- Rocks should not be placed closer to each other than 2 diameters (center to center)
- The angle of the line between the centers of the rocks should not be larger than 5°.
- The largest distance between the two rocks (center to center) should be 3.5 diameters.
The study was conducted by Staffan Lundström, Håkan Gustavsson and Elianne Lindmark, Division of Fluid Mechanics, Luleå University of Technology
Read the report in swedish here.