nautical charting surveys

case study

Tutukaka Harbour

Client: Land information New Zealand I Duration: 10 days I Date: 2014

Background

Tutukaka Harbour is located on the North East coast of the North Island, just north of the main centre of Whangarei. The Poor Knights Islands marine reserve, popular with boaties, divers and conservationists alike is close by. Tutukaka Marina is popular with local recreational vessels and is used as a stop over point for those vessels transiting between Auckland, the Bay of Islands and further afield. The narrow mouth of the harbour is guarded by Red Rock with a good deep channel lying just north. The narrow entrance which is difficult to see from the sea is surrounded by cliffs rising to bush and scrub covered hills.

The harbour and approaches are represented on nautical chart NZ5212 at a scale of 1:12,000. The area was last surveyed by the RNZN in 1962.

Requirement

Land Information New Zealand required a new hydrographic survey of the harbour and approaches in order to update the chart. A full bottom search was required using a Multibeam Echo Sounder (MBES) in conjunction with 30 days of tidal observations, bottom sampling, positioning of navigational aids and low water inspections for hazards to navigation.

Challenges

The entrance to the survey area is exposed to a swell from the North East through to the South East. The narrow entrance, steep cliffs, weed, swell reverberation and shallow upper harbour make for a challenging environment from within which to operate a MBES.

Solution

DML's 7m alloy Senator survey boat fitted with an over the stern mounted MBES and POSMV motion sensor proved to be a good platform from which to conduct the survey. The survey team's accommodation was located on the cliff tops above the harbour entrance. This enabled the team to view the survey area and to plan the daily survey activities taking into account actual swell, weather and tidal constraints.

During a break in survey operations DML took the opportunity to run its MBES over the wreck of the HMNZS WAIKATO, a popular local dive site. See http://diving.co.nz/go-diving/wreck-diving for more information.

Outcome

The survey objectives were achieved and it was delivered on time and to budget.

DML has conducted other nautical charting surveys for LINZ including; Hokianga Harbour (2015), Houhora and Mangonui Harbours (2015), Whangaroa Harbour(2014), Bay of Islands (2013), Poor Knights Islands (2011), Hen and Chicken Islands (2010), Patterson Inlet, Stewart Island (2009), Akaroa Harbour (2008), Milord Sound entrance (2008) and Abel Tasman National Park (2008).