Ship-Generated Waves and Induced Turbidity in the Göta Älv River in Sweden: Fid-Bau Portal

Ship-Generated Waves and Induced Turbidity in the Göta Älv River in Sweden

Göransson, Gunnel / Larson, Magnus / Althage, Jonas

Abstract

Ship-generated waves were investigated in the Göta Älv river, which is a major waterway on the Swedish west coast between the sea and Lake Vänern. Ships with a typical size of $85 \times 15 \times 5 m$ ( $length \times width \times draft$ ) travel at speeds between 5 and 10 knots, generating waves that cause sediment transport and erosion along the river bed and banks. Field measurements of the wave properties and turbidity were carried out during 17 ship passages, and comparisons were made with the most commonly used formulas for predicting ship waves. The formula proposed by the Permanent International Association of Navigation Congresses yielded the overall best agreement for the divergent (secondary) waves, whereas the drawdown (primary wave) could best be estimated from the vessel sinkage. The maximum recorded turbidity was mainly a function of the drawdown, and it could be well predicted from the parameterized bed shear stress. In conclusion, ship waves often induce bed and bank erosion in restricted waterways and, although simplistic formulas involve significant uncertainties, they are still useful tools for predictions. However, more studies are needed to determine the influence of a limited river cross section on the wave generation and the relationship between ship waves and sediment transport.