This chapter deals with the near-shore hydrodynamics that are important for sediment transport. It treats mean and oscillatory water levels and currents induced by waves, wind and tides. Relatively a lot of attention is paid to waves and wave-induced currents because of their effectiveness in transporting sediment in the surf zone.
The following aspects of waves are described:
- Linear wave propagation effects in shoaling waves (until wave breaking): increasing wave heights, decreasing wavelengths and refraction towards normal incidence (Sect. 5.2);
- Non-linear transformation of the wave shapes from initially symmetric, sinusoidal profiles, to asymmetric, pitched forward profiles characteristic of near- breaking waves (Sect. 5.3);
- Wave dissipation in the wave boundary layer and its effect on wave-orbital velocities, bed shear stress and net wave-induced flow (called Longuet-Higgins streaming) close to the bed (Sect. 5.4);
- Wave-induced water level changes in breaking waves such as the set-up (raising of the water level) at the coast, and wave-induced flow in breaking waves: a circulation current in the cross-shore direction (within the lower part of the water column an offshore directed undertow) as well as a longshore current along the coast (Sect. 5.5).
Subsequently Sect. 5.5 describes wind-generated set-up and currents. Section 5.7 is dedicated to tidal propagation in coastal waters. Last, Sect. 5.8 discusses some other long wave phenomena in coastal waters, viz. seiches and surf beat.