Formation

Manukau Harbour, second largest on the west coast of the North Island, has an area of about 150 sq. miles contained within some 240 miles of shoreline. The harbour originated in events that commenced less than 10 million years ago, when sea invaded much of the North Island. A large bay formed in the Manukau – Port Waikato area, possibly the result of northward tilting of the land toward a fault passing east through the present harbour entrance. Although this drowned area may have been connected by narrow straits to the Pacific Ocean, its development was essentially that of a bay into which the ancestral Waikato River flowed, depositing sediments and slowly extending the coast northwards. At the same time the current sweeping northwards along the west coast of the island was depositing sand in the quieter waters as it passed the threshold of the bay. The resultant bar grew until it emerged as Awhitu Peninsula, which, because of the scour of the ebbing and flowing tides, has not connected with the resistant volcanic rocks of the Waitakere Ranges. About 3 million years ago lava flows, erupted from centres in the Pukekohe-Bombay area, diverted the Waikato River to the west and, although at times it almost certainly followed the course of the present Waiuku River, the Waikato has since mainly discharged into the Tasman Sea. The strong, dominantly westward winds have drifted sand dunes up to a present height of nearly a thousand feet along Awhitu Peninsula. Within the last half million years the Manukau has been effectively sealed off from the Pacific Ocean by volcanism around the Tamaki Isthmus, except for transient connections at times of high sea level. Puketutu (Week's Island) and the neighbouring hills along the eastern side of the harbour, many since destroyed by quarrying operations, were formed in this period. Even since the Waikato River was diverted to the Tasman Sea, many small rivers and streams have continued to deposit sediments within the harbour so that it has long been shallow, with many changing sand bars, extensive mudflats, and fringing mangrove swamps. At low water only the larger channels are navigable, but the main restriction to navigation is due to the bars at the narrow harbour entrance where the mean spring low-water depth is only 3½ fathoms. Here shifting sand bars, combined with the heavy swell and breakers caused by the prevailing westerly weather, make navigation hazardous.

Origin of the Name

Maori traditions of the Great Migration tell of the canoe Tainui being hauled across the Tamaki Isthmus to become the first of the great canoes to reach the Manukau. The anxiety of Hoturoa, Te-Manuka-O-Hoturoa, as he steered Tainui towards the breakers at the harbour entrance, has been suggested as the origin of the name Manuka, first applied to the heads, then extended to cover the harbour, and since corrupted to Manukau. Other suggested derivations include “bathing place for sea birds” (manu, “bird”, kau, “a swim”), “place of the wading birds”, “nothing but birds”, and a corruption of the name of the ubiquitous scrubland plant, manuka.

With portages both to the Pacific Ocean and to the Waikato River, the Manukau was an important natural waterway to the Maori. Snapper, flounders, mullet, and shellfish such as scallops, cockles, and pipis, made it a valued fishing ground. Many villages were established around the shores and forts built on most of the volcanic cones. The effects of Maori settlement around the harbour are not certainly known, but quite considerable areas must have been cleared by fire to make room for cultivation. By the eighteenth century the Tamaki Isthmus was largely covered by ferns, manuka, and tussock, apart from the areas under cultivation; but to the south large areas of bush survived, and to the north-west the Waitakeres were bush clad. The principal trees were totara, rimu, matai, and puiriri, with kahikatea on the swamps. Kauri trees were scattered throughout, but were plentiful only at the northern end of Awhitu Peninsula and in the Waitakeres. Cabbage trees, nikau palms and the various tree ferns gave character to the bush, whilst colour was provided by the giant rata, the clematis, and, close to the water, the pohutukawa.

European Settlement

Rev. Samuel Marsden is believed to have been the first European to see the Manukau. Unlike the Rev. J. G. Butler who, after climbing Mount Wellington the day previous to Marsden's effort in 1820, described only the Maori settlements and plantations he had seen, Marsden specifically described the harbour itself. A few days later both missionaries crossed the harbour in a Maori canoe but could not navigate the entrance because of the heavy seas breaking on the bar.

The Manukau remained an important communications route throughout the early days of European settlement. During the Maori Wars local naval volunteers raided territories on the south side of the harbour from their base at Onehunga, established in 1847 as a defence outpost. Following the wars the harbour became important for its timber trade, kauri from Awhitu Peninsula and other timber from the Manukau lowlands to the south being rafted to the sawmills at Onehunga. Despite the treacherous nature of the entrance, the harbour was a regular call both for overseas ships and for coasters. Many ships have been lost here, the best known being HMS Orpheus, wrecked on 8 February 1863 with the loss of 189 lives. The early boom days of the harbour passed away with the construction of the railway south from the deeper and safer Waitemata Harbour. The first 10 miles were opened for traffic in 1873 and it is ironical that the puriri sleepers for it almost certainly came from the Manukau lowlands, across the harbour and through Onehunga. Growth of trade around the harbour has been slow and the urbanisation of the Tamaki Isthmus and the Manukau lowlands to the west of the harbour have been mainly related to the development of Waitemata Harbour. Most of the bush to the south has been cleared to make way for dairy and sheep farms, and the Waitakeres have been almost depleted of kauri. Today the harbour carries coastal shipping in slowly increasing tonnages to and from the industrial centre of Onehunga. An international airport, to be completed in 1965, is being built mainly on land reclaimed from the harbour near Mangere, where an extensive residential area is being planned. The Manukau waters still attract fishermen, and small but growing communities, such as Weymouth, which mainly depend on the recreational facilities of the harbour, have become established around the shores. Waiuku, on the south side of the harbour, is an important farming centre. Future development of the harbour will depend largely on the construction of a canal linking it with the Waitemata, where the tides are approximately two hours later. The canal would also shorten the sea route from the Waitemata to the west coast ports.

by Frederick Ernest Bowen, B.SC.(DURHAM), New Zealand Geological Survey, Otahuhu.

• Auckland – City of the Seas, Reed, A. W. (1955)
• South Auckland, Wily, H. E. R. L. (1939)
• New Zealand Geographer, Vol. 12 (1956), “Aspects of the Pleistocene and Recent History of the Auckland Isthmus”, Searle, E. J.