Work has recently been undertaken to stabilise the reservoir bed below the wall of the Inn dam and 73MW hydroelectric station near Ering in Germany. Contractor H Mailhammer decided to use a Case 1288 hydraulic excavator for the underwater work.

Divers at the Inn dam regularly inspect the reservoir bed and during the course of such routine analysis, it was discovered that the strong undercurrents in front of the turbines were causing reservoir bed erosion. As the water depth at the dam is approximately 13m the power station operator, Bayernwerk Wasserkraft, decided to stabilise the bed by filling the eroded areas with large irregular shaped granite boulders.

Instead of using cable dredgers normally utilised at these depths, the contractor decided to undertake the task with the Case 1288 hydraulic excavator configured specially for water engineering work.

Contractor Helmut Mail-hammer said: ‘We had often used hopper barges, with tip-up gratings or cable dredgers for this kind of work. As far as I know, nobody in the area has yet tried using hydraulic equipment fitted with long booms.

‘The currents here are so strong that simply tipping in granite blocks wasn’t feasible. In tests, the blocks were literally dragged towards the trashrack. The hydraulic excavator can reach all the way down to the reservoir bed, making it possible to position the blocks precisely.’