The characteristic black sand beaches of the west coast of Auckland extend from Karioitahi Beach in the south, to Rangitira Beach (north of Muriwai Beach) in the north and are interupted by the rocky shores of the Waitākere Ranges between Whātipu and Māori Bay. This section of rocky coast is home to a wide diversity of marine species with up to 290 species recorded on the west coast intertidal reefs alone. Species along this coast are well adapted to exposure to large swells, strong currents, cold temperatures and low light levels.
Coastal areas also provide habitat for many different bird species. These include important feeding and roosting areas for gannets in Māori Bay, or habitat for dotterels and fernbirds in the estuarine, dune and swamp areas of Whātipu Bay. There are also significant linkages to the Waitākere Ranges, which provides intact vegetation right down to the coast and to Te Henga Swamp.
Monitoring of beach profiles (sand volume and movement) on two of Auckland’s west coast beaches (Piha and Muriwai) has been undertaken since the early 1990s. This long-term data is valuable and is able to illustrate the dynamic nature of these beaches. This data shows that shoreline erosion is occurring at certain areas along the beach while other areas are accumulating sand. More recently beach profile monitoring was established due to erosion issues and protection work at south Muriwai and north Piha beach.
Sand erosion due to the southward migration of the North Piha streams (Marawhara and the Wekatahi) and storm surges was investigated by a team of multiple council units combined with the local community to determine the stability of the sand dunes and roadway above.
New techniques were used to monitor beach profiles and sand volume changes. Earth works to redirect the stream and reestablish the sand dunes to prevent the potential collapse of the coastal road followed. As a result, sand volumes have remained above set trigger levels and the sand dunes are stable.
Environmental quality along the West Coast is high due to the exposed nature of the coast and the distance from land based activities.