The Region’s coast includes parts of both the west coast and east coast of the North Island (Figure 8.1) and approximately 3,000 km2 of surface coastal water.

The west coast, which covers approximately 120 km from Waiinu Beach in the north of the Region to Waikawa Beach in the south, is characterised by narrow sandy beaches backed by sea cliffs in the north, and sandy beaches backed by a dynamic dune system from Whanganui southwards. The sand country comprises some 79,000 ha (3.6% of the Region’s area). The three main sources of sand are greywacke from the Tararua and Ruahine ranges, volcanic sediment from the Central Volcanic Plateau and sediment from the Whanganui Basin. The sediments are carried to the coast by the rivers and then tend to move east and southwards along the coast. The prevailing wind has blown this sand inland, forming an extensive network of dunes.

There are several estuaries of varying sizes. The 200 ha Manawatū estuary is the largest and is a wetland of international significance under the RAMSAR agreement. Most of these estuaries have extensive tidal flats and are specifically noted as habitat for birds, including many migratory species. The mouths of most of the rivers are constantly changing, moving south, forming spits as sediment is carried down the coast and then breaking through further north following floods.

This coast is a high energy shore, with wave heights commonly exceeding 3 metres. The dominant climatic feature is the wind, which is predominately westerly, and which has had a major effect on the physical shape of the west coast.

The east coast, which covers approximately 40 km from Cape Turnagain south to the Ōwahanga River mouth, is characterised by rocky platforms backed by cobbled or sandy beaches dotted with boulders. The landward coastal flats are narrow, backed by hills, and there is an area of sedimentary cliffs at Cape Turnagain. The tidal range along this coast is 1.2 metres.

The river mouths are dynamic and contribute large quantities of sand, gravel and silt to the seabed. The estuaries and tidal flats support a wide range of bird and fish life. The rocky coast provides good habitats, allowing for commercial fishing of paua, crayfish and kina. There is also a substantial finfish resource offshore.