WAITANGI TRmUNAL WOi ~%/4f K4 lCtlf 4rSftf A1- LU11 110 /-tF f-l-~ EAST COAST COROMANDEL PENINSUlAR ESTUARIES TAIRUA HARBOUR (WAI110) WHANGAPOUA HARBOUR (WAI 475) A Report on the Nature of the Tairua & Whangapou.a Harbou.rs, and the Way in which they have Changed since 1840 Report prepared by Gary Williams January 2000 G & E WILUAMS CONSULTANTS LTD OTAKI cd Wd,0:90 000c 90 'uer P899C9£ 90 : 'ON 3NOHd SW~IllIM 3 ~ 8 : WO~~ WAITANGI TRl8!1NAL THE NATURE OF TAIRUA & WHANGAPOUA HARBOURS COROMANDEL PENINSULAR INTRODucnON l'lUJIOSI! 1 This report provides information on the nature of the Tairua and Whangapoua Harbours, within the context of the larger estuaries, open to the sea, that exist along the east c;oast of the Coromandel Peninsular. It has been prepared for the Waitangi Tribunal, in response to a request by Garl Hirschfeld in respect of the Wai 110 and Wat 475 claims. 2 The aim of the report is: to firstly give Bome background information on coastal environments and the nature of estuaries, their characteristics and variability; and then to describe the Tairua and Whangapoua Harbours in terms of their natural form, the changes that have taken place since 1840, their present condition and their sensitivity to future impacts. The nature of the estuaries has been assessed and described in terms of the relative influences of the various factors or parameters that can be used to describe and categorise such coastal water bodies. Investigations 3 A general assessment of the estuaries of Tairua and Whangapoua has been carried out using information that could be readily obtained from inquiries of the relevant Regional and District councils, Government departments or Crown institutions and local people familiar with the estuaries and the history of the Coromandel Peninsular. There are a number of large estuaries, open to the sea, along the east coast of the Coromandel Peninsular, and different scientific and historical studies have been made on each of these estuaries. Information has then been drawn from the available studies on all these estuaries, to make an assessment of the Tairua and Whangapoua estuaries. 4 The series of large estuaries along the east coast of the Corornandel peninsular, of varying size, form and character, as described later in this report, are, from south to north. Whangamata, Wharekawa, Tairua, Whitianga and Whangapoua. Some environmental data is available on all these estuaries. A study of the effects on estuary sedimentation of changes in ~d Wde0:90 000e 90 'uer l>89ge9£ 90 : 'ON 3NOHd SW~llllM 3 ~ 9 : WO~~ Qualifications 11 I hold the qualifications of Bachelor of Engineering, Bachelor of Science and Master of Commerce. I am a member of the Institution of Professional Engineers of New Zealand. I have worked for the Water and Soil Division of the Ministry of Works and Development atits Head Office and Napier District Office, and for the Walrarapa and Hawke's Bay catchment authorities. I have also worked overseas in Mozambique and Papua-New Guinea. 12 Since 1987 I have practised as a private consultant, working mainly for regional and district councils on catchment and river management, and other water and soil resource investigations, including coastal processes and protection measures. 13 I have been involved in studies and works on many estuaries, through river management as well as coastal management, and been involved in studies and works on coastal lagoons and wetlands. In Hawke's Bay this included the Hawke Bay coast and Ahuriri Estuary, Whakaki Lagoon and Maungawhio Lagoon. I presented evidence to the Waltangi Tribunal on the nature of Te Whanganui-a-Orotu (W AI 55). I also carried out an investigation of the Te Whanga Lagoon on Wharekauri/Chatham Island (WAI 65) for the Tribunal. This involved a comparison of the Te Whanga Lagoon with other large coastal water bodies around New Zealand. On the west coast of the North Island I have studied a range of estuaries and coastal areas from Taranaki to Wellington, including estuaries at the mouths of the Pate a, Whanganm, Manawatu, Otaki, Walkanae and Hutt rivers. 14 My engineering experience has been related more to physical factors and physical modifications to coastal and river environments. However, biological factors are not only important in assessing environmental effects, they provide important indicators and guidance in the r;;arrying out of river and coastal management. As an engineer I have often had to draw on the knowledge of many different professionals, and utiUse this knowledge in solving prar;;tka1 problems and implementing management strategies. Findings 15 The findings ofthis study are based on the general assessments I have undertaken, given the information I was able to obtain and my professional experience over 25 years in the field of water and soil resources. They r;;an not be definitive, and should be read in the context of the jnformation limitations and the restrictions of a general assessment 16 The main findings can be summarised as follows: 3 pd Wdc0:90 000c 90 'uer P899Z9>: 90 : 'ON 3NOHd SW~IllIM 3 ~ 8 : WO~~ o The Tairua and Whangapoua estuaries are semi-enclosed estuaries, with substantial barrier spits at the coast They are made up of main channels, where the stronger currents of the tidal exchange are concentrated, wide intertidal flats and vegetated margins of estuarine grasses and mangroves. o These estuaries have a similar form and general character, but are significantly different because of the peculiarities of their coastal location and the nature and condition of their catchment. o The Tairua estuary extends inland as a wedge up a long rlv·er valley, with a single substantial river flowing through it There is a very substantial barrier on the south side, where the township of Pauanui is located. There is a Jower connecting barrler to the Paku rock outcrop on the :north side, and this gives rise to a more complex estuary form of side inlets where the township of Tairua is located. o The Whangapoua estuary has develoJ?ed in an area of converging river valleys, which have been mostly enclosed by a very substantial barrier spit It has a roughly circular shape, with a relatively very small and also apprOximately circular catchment There are a number of streams and minor rivers entering the estuary, with no dominant contributing waterway. o There is very little information about the nature and condition of the estuaries prior to European settlement. There would, though,. have been some modification of the coastal land and immediate environs of the estuaries by Maori. The natural form and character of the estuaries was, however, probably not significantly altered. o FollOWing European settlement there was a profound and devastating change to the catchment vegetation and over time to the immediate surrounds of the estuaries. The catchment vegetation was virtually destroyed by milling and fire, and this has given rise to greatly increased rates of sediment accumulation in the estuaries. The clear felling harvesting of the more recent plantation forests (of pines) has probably maintained high levels of sediment accumulation. o The number of people living around the estuaries was kept at a very small level until recent decades by poor access. Improving road access has given rise to a very rapid increase in both permanent and summer population levels. o The main threats to the estuary environment now, apart from continued clear fell harvesting of plantation forests in the catchments, is the impacts from the increasing population -in terms of bacterial contamination from sewage, nutrient enrichment, rubbish, power boats and the introduction of rapid spreading exotic plants, and overfish1ng. 4 Sd WdE0:90 000G 90 'u~f I>S99G9>: 90 : 'ON 3NOHd S~llllM 3 ~ 8 : wo~~ 12:36; 06 3b2bbf14 -~ Cllclr"1 H1rScI11p]d; Paqe 1 FROM : G & E WILLIAMS PHONE NO. 136 3626684 Jan. 20 2131313 el:31PM Pi COASTAL ENVIRONMENT Geological Formation 17 Coasts are dynamic variable environments that have been formed over recent geologic time, since the sea level stabilised at around the present level, about 6,500 years ago. 18 Over the last 2 million years (of the Pleistocene period) the general climate of the Earth has varied greatly, and the sea level has varied in concert, as ice sheets built up and melted. Short warm periods, similar to the present, have been int",rspersed with longer cold periods, when large ice sheets covered much of the higher latitude areas of the Earth. The climate has varied through the cold glacial periods with relatively wanner and colder times, as well as through the warmer interglacial periods. Recent research suggests that the climate of the present warm interglacial has been unusually uniform, with the sea level correspondingly stable. 19 Thus, prior to about 15,000 years ago, when there were massive ice sheets and glaciers, the sea level was up to about 135 to 150 metres lower than the present level. As the climate of the Earth warmed and the ice melted, the sea level rose, reaching its present level about 6,500 years ago, with a somewhat higher maximum level for a period about 5,000 years ago. 20 A new shoreline was formed, with a diversity of coasts: of eroding cliffs, drowned river valleys, and, where suitable sand and gravel material was available to reworking processes, long low barrier beaches. These low barriers have formed due to the longshore movement of material supplied by rivers or eroding coastal cliffs, or from the inshore movement of material on shallow sea beds. They separate shallow water bodies from the open sea giving rise to coastal lagoons and more enclosed estuarine river mouths. 21 Although most coastal systems would have developed their primary form soon after the sea level stabilised at its present level, coastal reworking processes of erosion and deposition continue, and many coasts are being actively reworked.