For many years, the Bavarian Water Resources Administration used rope nets to entrap the wooden debris. The advantage of this construction is:
• simple building equipment can be used
• commercial components and common techniques can be used
• rope nets are inconspicuous and almost do not disturb the landscape.
The main structure to bear the forces consists of ropes, which are spanned across to the flow direction over the torrent. The nets have a distance of about 0,50 to 1,0 meter to the river bed so that smaller floods without wooden debris and bedload can pass unhindered.
The research project was carried out at the Institute for Hydraulic an Engineering at Technische Universität München, to answer the following questions:
• How is the process of the entrapment in rope dams proceeding?
• Which forces occur and what are the main parameters of influence?
• Which recommendations for the construction of net-dams can be given?
In different model tests the entrapment process was analysed and the main parameters of influence were worked out. Furthermore a full-scale nature test on rope net barriers was realized to investigate dynamic loads in the beginning of the entrapment process and to work out the influence of elasticity. Significant for the design are only the static loads, which in nature are about 20 to 30 % higher then in model due to a greater volume of fine material with less dimension and sagging ropes respectively nets. The function of the net barriers was proved. The results lead to a design concept for rope net barriers.