“MetOcean Solutions has worked exceptionally hard to assist the Port of Geraldton with its surge problem. The product they now deliver is heavily relied on when scheduling shipping. The efficiencies gained in reduced labour costs to port users are significant, but is the contribution to safety that represents the greatest gain. In 2005 there were 242 parted ships lines at Geraldton. Following the developments in forecasting Long Wave effects at Geraldton, last year there were only 30 parted ships lines. This was the lowest number of parted lines since records have been kept. MetOcean Solutions is keeping Geraldton Port efficient, and port workers safe.”
Captain Ross Halsall, Acting Harbour Master, Port of Geraldton.
Observational wave data can help ports manage the onset of long wave events. In recent work for Geraldton Port (Australia), we improved our harbour long wave forecasts by integrating wave buoy data from two upstream locations into the short-range predictions.
Long (or infragravity) waves are created when swell waves interact with the coast and result in water level oscillations with periods much longer than the original swell waves. Long wave periods of 60-120 seconds are typical, and these are very problematic because their wavelength is similar to the size of ships. When such waves enter a harbour the moored vessels are energised, causing dangerous surging which can break lines and put personnel in danger. As a result, ports often have to close when long wave heights exceed a safe threshold.
Accurate forecasts of long wave height can help ports increase safety, reduce unwarranted closures and effectively plan for reopening. For the past 11 years, MetOcean Solutions has provided a specialist long wave forecasting service that ports and harbours throughout New Zealand and Australia have come to rely upon.
“Our scientific research over many years provides the basis for a robust prediction system,” explains Senior Oceanographer Dr Severin Thiebaut. “We use a semi-empirical technique to establish the relationship between the offshore wave spectra and the long wave height at each berth in a port. It's a method that we have tested at more than 30 locations worldwide”.
The forecast wave spectra is derived from the suite of global and regional numerical models run by MetOcean Solutions. Geraldton Port have been using these predictions to guide the harbour operations since 2007. Predictions have proved very reliable, but sometimes the arrival of a swell front may differ from the forecast by a few hours as the exact timing is difficult to resolve perfectly with a spectral wave model. To supplement the long wave forecasts, we developed a new technique using real-time wave buoy data to improve the short term predictions and better detect occasions with a sharp rise in long wave energy inside the harbour.
‘“The goal is to ensure that our port clients are never surprised by weather events,” says Dr Thiebaut.
The Department of Transport maintains wave buoys at Rottnest Island and at Jurien Bay, some 370 km and 170 km to the south of Geraldton, respectively. The live data from these buoys, updated at 30 minute intervals, are used to track the progression of swell up the west coast of Australia and provide harbour long wave predictions some 5-6 hours ahead.
“Using the live buoy data provides additional confidence to the standard forecasts. In particular, it allows us to accurately capture any rapidly rising long wave events. It also gives the port operators a better idea of when wave heights will decrease to safe working levels. Geraldton Port accesses the forecast information through the web-based MetOceanView platform and through their local environmental monitoring software. On the same plot we show the measured long waves at the berth along with the values that are forecast by our standard system plus those predicted by the buoys.”