Lunker Structures in the Rubicon

After Paul Brown returned from America where he studied trout habitat, he installed a trial structure in the Acheron river, not far up from the Breakaway.

This first attempt allowed Paul to trial different structures. The principal of a lunker structure is to provide and undercut bank to provide shelter for fish from predators, and prime sites that fish can use as home territory. An inventory of fish numbers and stream structure was conducted and then the lunker structure was installed. Later assessment would indicate an increase in fish numbers due to the installation of the new habitat.

This first successful structure had the desired effect and now a much larger trial is being conducted on the Rubicon river downstream of Thornton township. When a river reaches its mature stage in the low land flat country, it is inclined to be deeply incised into the flood plain with high banks and meandering flow. Often the corners suffer serious erosion with collapsing banks and silted up runs and pools.

Lunker structures are designed to control erosion and provide secure trout habitat at the same time. They are benches set into the bank and covered with stone and earth. The benches are set at surface level and therefore provide space for cover underneath for fish to hide. They look like large red gum picnic tables. They are secured to the bank and the bed of the river with steel rods driven into the bottom. The top of the table is then loaded with stone and earth and the bank is battered back on an angle.

Once it is grassed over and replanted with some vegetation, these structures should start to look more like the natural landscape. You can see from studying the photographs carefully the 'Benches' set just below the surface. In the distance the Bobcat is returning stone and earth over the bank.

We look forward to the assessment to compare it to the original inventory to see if fish colonise these new structures in larger numbers.

~ Geoff Hall