Shore-connected breakwaters are also called moles or jetties. The purpose of breakwaters is to protect a harbour entrance against wave action and to prevent sedimentation in the harbour entrance. Another purpose of breakwaters is to confine the flow in an outlet (i.e. to act as training works). In order to prevent sedimentation in a harbour entrance, the breakwater must extend through the complete surf zone during storm conditions. Moreover, the breakwater must withstand the design wave without unacceptable damage.

Breakwaters can be classified into three main types: rubble mound breakwaters, vertical breakwaters and composite breakwaters.

The rubble mound breakwater is flexible. Hence, it can follow small settlements in ground level. The construction is relatively simple, but requires large amounts of material in deep water (see Fig. 72 and Fig. 73). Note that in the design of a rubble mound, the armour units are required to prevent erosion of the structure's surface, the core provides a relatively impermeable barrier to the transmission of wave action
through the mound, whilst the underlayers not only provide a suitable support for the armouring but also .prevent the fine core material from being washed out through the voids within the armour layer.