Shallow waters in harbour entrances
Tuesday, 24 May 2011 3:00 p.m.
Shallow conditions in the Ōhiwa and Ōpōtiki harbour entrances are creating potentially hazardous conditions for boaties.
Bay of Plenty Regional Council has carried out depth soundings
for the harbour entrances to confirm water depths.
Regional Council Harbourmaster - Eastern, Brian Spake said the recordings have shown the water is now shallower in the harbour entrances. The deepest parts of the entrances have also shifted.
"Both Ōpōtiki and Ōhiwa harbours are enclosed by sand bars, and the best available water lies to the west [Ōpōtiki] or north-west [Ōhiwa] of these entrances," Mr Spake said.
For the Ōpōtiki entrance, the deeper water lies next to the western beach in the direction of Moutohorā (Whale) Island. The water is only 0.6 metres deep at 'chart datum'. Chart datum is a water level so low that the tide will seldom fall below it.
Mr Spake said better depths were recorded at Ōhiwa, with 1.1 metres at chart datum.
"Boaties should cross the bar heading out to the north-west on a compass (magnetic) heading of 310 degrees. Inbound bar crossings should be carried out with a south-east heading of 130 degrees.
"The shallow inner bar extensions will need to be further negotiated once they are across the main outer bar," Mr Spake said.
For the next three months the lowest tide predicted to fall is
0.3 metres so the shallowest depth for the Ōpōtiki entrance would
be 0.9 metres.
The Harbourmaster has restricted navigation of the Ōpōtiki Harbour entrance to two hours either side of low tide for all vessels.
Ōhiwa Harbour is not currently restricted but will continue to be monitored, Mr Spake said.
A three hour restriction either side of low tide remains in place for the Thornton (Rangitāiki River) entrance.
The Whakatāne Harbour entrance is currently unrestricted.
The following figures are displayed in depths above chart datum (chart datum is a water level so low that the tide will seldom fall below it).
Boaties should add the height of the low tide level to give the actual available water depth over the bar at low tide.
Opotiki entrance 0.6 metres
Ohiwa entrance 1.1 metres
Thornton entrance 0.3 metres
Whakatane entrance 1.9 metres