A wave-current numerical model is developed for interactions between waves and current fields. Investigations are focused on the effects of currents on surface fluctuations, wave height and mean water level (set-down) distributions. Also, experimental studies on wave-current interactions are conducted in a wave flume and onedimensional model predictions are compared with the experimental observations and wave-current analytical solutions. Comparative results depict that the model simulates the interactions quite well Results also indicate that intensity and direction of a current modify wave crest and trough amplitudes. And wave-current interactions are significant in a region where the magnitude of a current is greater.
In nature, waves rarely propagate on quiescent water; more generally they travel on currents (Dalrymple & Dean, 1975). In coastal region, wave-current interactions are dominant near a river inlet or a harbor entrance and interactions mostly take place due to tidal current and river discharge. A current field modifies ocean wave spectrum (Hedges et al., 1985) and this spectrum modification changes the design parameters of offshore structures (Ismail, 1984). Sumer and Fredsoe (1997) show that scour depth around the head of a verticalwall breakwater increases considerably for regular wave attacking in presence of a co-directional current. Wave-current interactions are most significant in the shallow water region where wave properties - for example, wave heights, wave lengths, wave directions, etc. - are modified due to a current. Thus, understandings of wave transformation in a wave-current coexistence field bear a great practical importance for scientists and engineers. The mechanism of wave-current interactions was presented by Longuet-Higgins & Stewart (1961) and they introduced the concept of radiation stress. Method of wave action (Bretherton & Garrett, 1968) and mean energy level concept (Jonsson et al., 1970; Jonsson, 1990) are also introduced for interactions.
