Monday, November 22, 2010

Beach Five update

Visited beach 5 today and took these photos of the fore-dune. To the West the dune looks alot more stable compared to the view East where the active undercutting is visible. The seaward half of the inter-tidal zone is fluffy with the transported sand. I also counted 6 dead Shearwaters. Also found my 1st Pipi from here with a Natacadea borehole. Usually these predatory snails are out competed by more efficient hunters.

Wednesday, November 17, 2010

What is a Spit?

The geomorhpic definition of Spit is a sandy bar projecting from the mainland into open water. Spits are formed by deposition of sediments moved by longshore drift. (here is a wikipedia link on spits, if you want more details)

So the Big question; Is Point Symthe a Spit?

Well it is widely described as a spit in tourist literature guide books, Often as Victroia's largest spit. However there may be a few problems calling it a true spit
1) The Andersen inlet estuary is no longer "open water" and there is a very strong tidal inflow and outflow cutting across the longshore drift
2) Observations in this project suggest that the longshore drift does change directions and has been larger going southwards for the past few years
3) It doesn't have the characteristic hooked end.

Yet physically it is a very large continuous section of sand and the present situation may represent a very late stage of spit development. Where by the entrance to Andersen inlet may close over with a continous sand bar from Point Symthe to Inverloch.

However as Andersen inlet gradually fills with sediment (not sure if anyone is accurately measuring this) The effects of the tidal flows (it is the same amount of tidal change but in a progressively shallower inlet) mean that there is now considerable erosion cause along the main chanels giving outlet to the sea. These infact are behaving like a meandering streams thrashing back and forth across the inlet floor and heavily eroding the coast & beaches but just at very specific locations (where the chanels curve most).

Who will win? Longshore drift or the tidal flow from Andersen Inlet.