Impact of ship waves on the sediment transport in a nature friendly bank protection

With regard to non-tidal, confined waterways subject to heavy shipping traffic, the realization of a more ecologically sound bank protection is quite a challenge. The technical-biological method under study consists of off-bank timber piling in combination with (reed) vegetation in the shallow water zone behind. Being an open, semi-natural system, an on-site measurement campaign was conducted to identify and quantify the main sediment transport processes caused by ship wave action. It is found that the critical bottom shear stress is exceeded during the greater part of ship passages. Sailing ships also increase horizontal flow velocities in the direction of the river bank, giving rise to a potentially large impact energy with which the returning water mass of the drawdown trough hits the river bank. Sediment entrainment and redistribution of bed and bank particles is thus effected. However, a direct cause and effect relation between ship-induced hydrodynamics and sediment erosion and deposition mechanisms is only partly unraveled.