MARICO Marine NZ Limited WELLINGTON HARBOUR PORT AND ...

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Report No: 05NZ104 WELLINGTON HARBOUR Issue: Issue 1.1 Operational Risk Assessment severe sea conditions occur during southerly gales, it is during rising northerly winds that most leisure users require assistance, most frequently from engine failure or inadequate power to return to shore against a strong offshore wind. Although not within the scope of this risk assessment, there have been a number of diving accidents along the south coast where divers have been swept away by strong tidal flows. This is similar to the poor recreational diving statistics of the Marlborough Sounds. A Marine Reserve is proposed for an area of this coast around island Bay and the former RNZN frigate WELLINGTON was sunk in 2005, seaward of Island bay (in 23 metres of water). This is likely to result in an increase in the number of small craft navigating in the area for fishing and diving purposes and possibly sight-seeing purposes. Future SAR response plans for this could need to be considered. 5.2.3 Area A – Incidents of Note There are records of vessels being wrecked on the Wellington approach shoreline going back many years. However the recent data record is dominated by reports of mechanical failure. Such a record only underpins the conclusion that the Wellington approach is an unforgiving area. Mariners who experience difficulty with their vessels tend to report problems at an early stage - they are literally between a rock and a hard place if mechanical problems cannot be rapidly rectified. It is an area where a planned and rapid SAR response is justified, with early precautionary call out recommended. 5.3 AREA B - ENTRANCE Area B essentially covers the entrance channel and the bar. The entrance into Wellington harbour lies between Palmer Head to the west and Pencarrow Head to the east. The entrance is divided into two channels by Barrett Reef, a rocky outcrop of about 5 cables length lying about 4 cables south of The Pinnacles in a north-south direction. The main channel is east of Barrett Reef, approximately 7 cables width, with depths 11.3 metres over the bar and 16 meters maximum. A smaller secondary channel, Chaffers Passage, lies to the west of Barrett Reef. This separates Barrett Reef from the shoreline of The Pinnacles and Point Dorset. The controlling depth of this passage is 9.6 metres with a width of about 2 cables at its narrowest point, but there is at least one sunken rock and also kelp beds in the area. There are no Aids to Navigation Greater Wellington Regional Council / CentrePort Ltd Page 29 of 102
Report No: 05NZ104 WELLINGTON HARBOUR Issue: Issue 1.1 Operational Risk Assessment for Chaffers Passage and local knowledge is essential. In practice only leisure craft, small commercial and fishing vessels use this passage (i.e. none requiring pilotage). This passage affords shelter in north northwest winds, and also allows smaller craft to keep clear of larger vessels using the main channel. Chaffers Passage may be dangerous in strong southerly conditions, when heavy surge or swell are present. The narrow bottle neck shape of the entrance channel runs north for a little under two miles between Barrett Reef Buoy and Steeple Rock beacon, this area being known locally as ‘The Narrows’. The western shoreline is characterized by rocky ledges and pinnacles extending seaward from a wave cut platform, while to the east a larger platform, under 10 metres depth, runs along the eastern side of the channel from the Eastbourne coast. Makaro/Ward Island marks the northern extremity of this shoal area, while the Front and Rear leading lights help to mark its western boundaries. The navigable channel for large vessels (i.e. water depth over 10 metres), narrows with distance north (around 7 cables at Barrett Reef to 4 cables off Steeple Beacon). The channel minimum depth (of 11.3 metres) occurs close west of the leading line and about one mile north of the entrance. Depths along the line of the leads and inward/outward tracks taken by large vessels vary between approximately 19–11.3 metres (the average being 14 metres). With the width restriction formed by the platforms on each side, there is an effective channel width of six cables or less for large vessels until the deeper waters of the harbour basin (Area C) are reached. 5.3.1 Channel Morphology The section between the south end of Barrett Reef and Steeple Beacon (‘the Narrows’) is also the area of least depth. If the seafloor profile was examined as a cross-section, it would be seen as a bar-like formation, connecting the deeper harbour approaches to the basin of the inner harbour area. Although Wellington entrance does have a bar profile and therefore occurrence of heavy breaking waves, depths do not appear to change rapidly, nor is there a counter current as in other bar harbours (e.g. Greymouth or Westport). Academics would therefore not refer to Wellington as a Bar Harbour, but for navigation in severe weather the effect is the same. The seafloor is generally fine sand and is mobile during storm events, but this does not significantly affect depth, rather the pattern of sediment distribution changes. Underlying gravel is exposed periodically, particularly Greater Wellington Regional Council / CentrePort Ltd Page 30 of 102
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