Beach erosion – it’ll all come out in the wash!
Beachgoers around the Bay have reported higher high tides and lower low tides since the Channel Deepening at the Entrance was completed in September 2008. There’s also been unprecedented beach erosion, particularly at Portsea.
When waves break the turbulent water surges up onto the beach… then runs back again. The returning waters can cause strong rips and underwater currents which take sand with them.
Mini rip at Middle Park (April 2010)
Each beach has many rips of varying size and strength, which can change location from one tidal cycle to the next. The stronger the wave action the stronger the rip. These currents carry inter-tidal sands into deeper water. The moving sands are usually picked up by longshore drift to eventually return to shore further along the coast.
The Hydrodynamics and Coastal Processes Head Technical Report (January 2007) prepared for the CDP noted that tidal currents are the major sediment transport mechanism within ‘the Sands’ (south of the Bay). The report also predicted an increase tidal current strength but generally confined to the area of the deepened channel.
Baykeeper suspects that in the Portsea case it’s likely that the deepened channel is swallowing sand which would ordinarily have returned to the beach. Time and tide will eventually tell!
This is fascinating (and alarming) information. My thanks to you for the learning (and to Canny Granny for alerting me to your blog). Best regards, P.
It is already “coming out in the wash” quite thoroughly, if a recent article in the Portsea local paper, the Mornington Peninsula Leader, is anything to go by. Beach LOSS, not just erosion, plus other events involving changed tidal behaviour, has been observed over the last couple of years, and is galvanising some locals into action. To catch up with the latest from down near The Heads, follow this link:
http://mornington-peninsula-leader.whereilive.com.au/news/story/beach-debacle-fears/ . And, as one commentator reminds us, it is not only the south of the bay which should concern us. Don’t forget the underwater toxic dump sitting in the middle up near Mordialloc! Is anyone willing to open a book predicting the year when we will hear more about that?
Have a look at the solution that the clowns that manage the bay have done on Portsea beach.
They have dumped hundreds of tons of rock either side of the pier ruining the once pristine beach forever. It is a disgrace. the State Government are vandals nothing more than that.