Griffiths McMillan JV (GMJV) is tasked by Wellington Water and the Greater Wellington Regional Council with drilling for a new water source for Wellington City, with the goal of providing an alternative supply in the event of a severe earthquake. GMJV approached Heron Construction Company to supply the jackup barge and support tug for the project. The target aquifer, however, lies beneath Wellington Harbour - just north of the Miramar Peninsula. A marine drilling rig is required for the operations, which means that operations are very sensitive to the wave conditions.
MetOcean Solutions has been supporting Heron Construction in their specialist marine activities with high resolution forecasting for the last decade. Managing director Greg Kroef says, “We rely on the forecast guidance from MetOcean Solutions wherever we are working in Australia and New Zealand. So, when the need arose in Wellington, we approached them for the best possible weather forecasting system for this site.”
The drilling job in the harbour requires very accurate predictions of wave height. However, the oceanographic conditions in Wellington Harbour present significant challenges for forecasting, with ocean swells entering from the south along with local seas generated by the infamous capital city winds.
Oceanographer Dr Peter McComb and his science team extensively studied the harbour dynamics for the recent harbour deepening project. “The drilling location is affected by both the southerly ocean swells and the short local wind seas,” explains Peter. “Our forecasting model has to deal with multiple and sometimes simultaneous sources of wave energy, plus discern how those waves refract and transform due to the shape of the seabed and the harbour tidal hydrodynamics.”
The operational SWAN wave model for Wellington Harbour has a spatial resolution of 80 m, and is one of nearly 200 forecasting domains that MetOcean Solutions run four times per day for various parts of the planet. This high-resolution model is coupled with the tidal hydrodynamics to capture the effects of the ebb and flood flows through the entrance on the waves, and it has spectral boundaries prescribed by a 3-stage nest into our global WAVE WATCH III wave forecast model. The model system produces the hour-by-hour wave conditions for the coming 7 days.
“However, just having a wave forecast model is sometimes not enough to ensure safe operations - especially in Wellington which is notorious for rapid changes in weather conditions,” continues Dr McComb. “So we decided to deploy one of our directional wave buoys near the drilling site to provide real-time monitoring of the wave conditions along with instant verification of the forecast accuracy.”
The wave buoy sends data ashore every hour so everyone involved can monitor the sea conditions in real time. See for yourself at: http://wavebuoy.metocean.co.nz/wellington
“When ingested into the MetOceanView forecasting system, we co-plot the measured and the forecast wave heights. This is the most honest representation of forecast accuracy, and allows users to gain confidence in the timing and the magnitude of the wave predictions. The recent storm from 13 July was a very energetic event, but we captured it perfectly from 3-4 days ahead.”
MetOceanView ingests observations from over 10,000 sites every day, including 252 locations around New Zealand.
For queries about ingesting site-specific data, contact firstname.lastname@example.org.