Over the years our tags have mainly been used to track fish and other aquatic animals or monitor equipment in the submersed environment. Occasionally, we get the opportunity to take part in projects that are a little more out of the ordinary. The Norwegian Water Resource and Energy Directorate (NVE), whose main objective is to monitor the water and energy supply, is conducting a project to restore fish habitats in rivers which are rebuilt to avoid dangerous erosion and landslides. Quite different from the standard delivery of fish tags, we helped them drill and tag a number of river rocks!
Many rivers are reinforced and engineered to save houses and lives from extreme weather and flooding. Riverbed profiles are reinforced with large and sharp rocks, concrete, and river sides are built up to avoid erosion and control the energy of flood water rushing down through urban areas. As a result, the habitat of fish and river ecosystem is often destroyed, and the river must be rebuilt with finer sediment, gravel and natural occurring river rocks. With every flooding, these substrates tend to be washed away and disturbed. The rivers are left unsuitable as spawning grounds and habitat for juveniles, as well as the pass-ability for larger fish is reduced. To prevent this, exposed areas need to be re-filled with gravel on a regular basis, which is an expensive and invasive process.
To secure and preserve viable river systems, field tests are now carried out in Kvernbekken, a stream located in Meråker, central Norway. Here, the river bed was raised about 2 m with larger rocks and restructured with turns and ponds to avoid erosion of sensitive clay. The riverbed has been carefully rebuilt with naturally occurring sediments and gravel. The objective of the study is to learn how to make a rebuilt river self-sustained with habitat substrate. In a couple of designated, upstream river turns, gravel depots were created which could feed into the new section during floods. To document how the gravel will travel and how the depots perform, stones of predetermined sizes were measured and tagged with acoustic tags and placed in the different depots. Once they are out in the system, they will be detected by standalone receivers along the stream, as well as real time receivers for manual tracking over time.
We were lucky enough to go out in the field with NVE and tag some rocks!