The Wirral Peninsula is situated in the north-west of England (see Fig. 117). Its north coast lies within Liverpool Bay and it is exposed to waves generated in the Irish Sea. The maximum fetch is only about 200 km but the significant wave height may reach 5.2 m or more annually in Liverpool Bay, 7.3 m or more once every 50 years on average.

The tides dominate the movement of water in the Irish Sea with an average spring tidal range of about 8.1 m along the North Wirral coast. In addition, storm surges caused by a combination of low atmospheric pressure and strong onshore winds may raise water levels in the area by up to about 2.0 m with a frequency of about once in 50 years. Tidal currents along the coast may reach 2 m/s or more.

The North Wirral Coastal Defences incorporate a number of breakwaters (Davies, 1989). These structures are designed to stabilise the beaches by encouraging the deposition of sand: the breakwaters both reduce the wave activity immediately adjacent to the shoreline and help to divert the tidal currents offshore.

At Leasowe, there are two rock armour breakwaters constructed during 1981 and 1982; one of them is shown in Fig. 81. The crests of these two breakwaters generally remain exposed. However, further east at New Brighton there are five breakwaters which become submerged during some high water conditions. These structures, built in 1984 and 1985, are armoured with precast concrete units (see Fig. 118).