MuttonBird forum posts in last 60 days

Thanks again Jake. This a very complex subject, and may only be of interest to you and I. But for the benefit of anyone watching this post, here is a synopsis of my rhetorical question:

At low ocean tidal level the Rip is basically constrained by the Lonsdale Reef on the west, and the Nepean Reef on the east. Of course these are offset somewhat, but they are both 'dry' at low water. All the high tide flow action takes place when these are covered. There is a time during each tidal cycle when the level 'inside' becomes more or less level with that 'outside'. This is influenced by tidal nuances and, importantly, prevailing pressure and wind. And as Jake correctly points out that time depends on which part of 'inside' we are considering.

The important point is that the highest levels 'inside' never get anywhere near the highest ocean levels 'outside', (and vice versa for low water). This means that there is always potential for much higher levels in the Bay. Jake, you quote BoM as logging annual sea level rise of 2.3mm/year. This does not sound much, but that could represent ~50mm in 20 years (my likely max lifespan!). On an incoming tide all that extra depth will flow in across a wider cross-sectional area than at present. How much will the Bay rise?? To answer my own question, I posit that plus 50mm outside will result in 100mm inside. It is the only possible hydrological consequence of the 'weir effect' of the Rip geology. This is an intuitive proposition, as I am not aware of any serious modelling to help us.

After close to 70 years of observation of the Nepean coast of PPB, I believe I can see evidence of a significant increase in highest high tides. These are,of course, heavily influenced by wind. After the passing of a low pressure system and days of SW gales, tidal levels are approx 30cm higher than 'normal'; and after high pressure and easterly gales, about 30cm lower (at least on the southern coast of the Bay). There is a definite change in high water coastal erosion between say Rye and Portsea. And it is absolutely certain that near-shore currents,around Portsea and Sorrento, have changed since deepening operations in the Rip.

My original suggestion for Jake to consider was that of much higher sea level - one foot or one metre or even many metres. Clearly, I will not live to see this, but, as a scientist, I believe in the veracity of these long term predictions (I might be starting to lose some some viewers now). Anyway the effect on the PPB hinterland and much of suburban Melbourne would be catastrophic!

Happy sailing, floss daily and build on a hill!