Tuesday, December 28, 2010

Reading the sandbars

Most of the action on the beach at the moment is occurring down at the low tide line. If you look there is extensive development and changes in the sand bars. You can read the direction of the longshore drift of the sand by analysing the sand bars.

Look to find which end the bar is connected to the beach. If this is at the southern end of the sand bar the net longshore sand drift will be going to the north. If connected at the northern end the net longshore sand drift will the going south.sand drift

Note: Diagrammatic only & not to scale

The mechanism of longshore drift on a long sweeping beach like Venus Bay is fairly easy to explain. The wave hit the beach slightly obliquely (this depends of ocean currents and nearby coast and sea floor topography) and carry some sand particles up the beach in the same direction that the wave was travelling as it hit the shore. Then the wave receded but now the water runs down the gradient of the beach (ie at right angles to the beach) so some sand is again washed back but following this new flow direction. so the sand particles zig zag up and then down the beach moving them along the shore a little as each wave carries them up the beach.

Very much related to the development of sand bars along the Venus Bay beach are Rip currents. These are feed with water but the lagoons and depressions that form behind the sand bars water coming over the bars has to run along this hollow to get back out to sea. Sometimes it quickly erodes deep gutters (a favourite pace for surf fisherman at higher tides) or pot holes. Often the sand near the deeper pots holes is very loose and unconsolidated because it is recently transported there.

Over the past few years the longshore drift has been dominantly to the south but this year It would appear that the general sand drift has turned to the north. It would be nice if all those interested observed the sandbars and posted their observations of sand drift  as comments here or as messages  on Twitter using the either hashtag #VBOP or to @VBOP

Eg for twitter

@VBOP beach one sand bars show sand drift to north

Friday, December 24, 2010

Beach One Christmas Day

Beach One Venus Bay

Christmas sunrise at Beach One, Venus Bay. As imageo mentioned in his last blog, the low air pressure and Lunar influence combined might lead to further sand movements and erosion along Venus Bay's coastline. The picture left has mounds of sand running parallel to the shore, and right shows how uneven the erosion to the berm is, as it persists in these deeper troughs. The fore-dune has experienced some erosion in places too.
Behind it the primary dune is suffering blow outs, often caused by people walking up and over the dune system, then enlarged by prevailing winds. We would remind people that besides being important habitat, the dune vegetation plays a critical role in stabilising the dunes, ie the beach. Besides that have a happy and safe Christmas, enjoy the beach and drive carefully.

Sunday, December 19, 2010

Lunar Eclipse @ Sunset Tuesday 21st.!

For those interested, and clouds permitting, you will be able to a partial eclipse of the moon should be visible just before sunset as the "full" moon rises (approx 8:40pm) and best time to view will be as the sunsets, with the moon still low on the horizon and appearing larger than usual. The partial eclipse will reach it midpoint around 9:15PM and be complete by 10pm It should have a reddish colouration over much of the moons surface (not as complete as shown in photo from the June 2009 lunar eclipse but distinctly reddish all the same).

The best places to view the eclipse at Venus Bay will those places with a good view of the eastern horizon, such as the overflow Carpark on the way to beach one, OR on the Venus Bay/Lower Tarwin bike track at the beginning of Jupiter drive OR at the boat ramp at Estate 2.

Wikipedia has more details on this eclipse. This Blog has details of best viewing time for some Australian cities.

The 21st also marks the summer solstice (the shortest night of the years), The full moon and the tails of low air pressure and cold front (bringing the cold and cloudy weather) may bring higher than average tides and a slight possibility of more erosion and sand movement at the top of the beach. All in all a good night to get out and take a look at what is going on, albeit with a raincoast and umberella.

Thursday, December 2, 2010

Beach One berm watch

This is the state of the berm at Beach One on 2nd December. View is towards Southeast during the low tide, at 11 AM.
Note the lower inter-tidal zone with sandbars and sitting water.