Someone from the Huon who talks endlessly about the details of tides or an interesting natural phenomenon? The 1.39m spring tide early on Saturday, 3rd Jan provided us with the best opportunity to refloat Gretchen for months. If we missed it, we would either have needed mechanical assistance to get her back in the water or wait until the spring tides in June which reach a peak of 1.49m on 15th June. It also provided the opportunity to calibrate the time of high water at Franklin against the high predicted for Port Huon – the nearest site for which BOM publishes tide predictions. Interestingly, on both 2nd and 3rd January, Franklin’s high water peak was about 40 minutes before the predicted high at Port Huon. This doesn’t seem to make sense as the incoming rising water must come past Port Huon to reach Franklin. One suggestion (thanks Ryan) is that as the rising tide advances towards Franklin the narrowing and shallowing of the Huon estuary squeezes the tidal flow to create a slight ‘mound’ of water or wave front which appears as the peak of the tide in Franklin ahead of the predicted high at Port Huon. This is the same process that causes the tidal bores on the Qiantang River in China, the Amazon in Brazil and the Severn in the UK. Ours isn’t nearly as dramatic as the more famous bores, but then towns on the Bristol Channel leading into the Severn River have tidal ranges up to 13m compared to our peak range of about 1.3m.
You can decide which definition best decribes a tidal bore.
