Having fun …BUT

 
These very noisy mechanized wave runners are obviously have fun, albeit in a high risk way BUT they certainly didn’t impress the other beach one users. The fishermen were muttering about yoboos, the pipi gathers were yabbering about the strong smell of the spilt fuel and the tradition board riders shaking their heads in despair, What I notice is their wasn’t a single bird to be seen anywhere close by. Yet up at beach five there were plenty.
 
Is this a case of NIMBY over-reaction or is jet skying one of those recreations that really does needs to be controlled in national parks?

Foam & More Foam

Today the swells as pounding in, the wind almost gale force but the waves do not appear to be eroding the dunes (they might tonight with a high tide corresponding with a low pressure and very strong onshore winds). What is most amazing is the surf foam racing across the sand and on up the dunes.

Taking on the winter shape…already

The beach is loosing the distinct flatter area of dry sand from the upper beach zone and a continuous sloping curve, typical of the winter shape (or winter berm) has quickly developed for the beach profile. The reason is clearly the strong onshore winds, strong swells and powerful waves crashing onshore. The highest tides are however not reaching the scarps from previous erosion.

In previous years these changes have more typically occur in April/May.

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.

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

Understanding Longshore Drift

When Waves arrive at the beach at an angle to the shore line, sand will be pushed up the beach in that direction however in the backwash the sand will usually moved directly down the beach, perpendicular to the shore line. So the sand follows a zigzag pattern. The result is a net movement of sand along the beach. An enormous amount of sand can moved in this manner.

By looking at new sand bars you can determine the longshore drift. If the sand bar is attached to the beach at its northern end the longshore drift is to the south. Conversely if the sandbar is attached to the beach at its southern end the longshore drift is to the north.

Longshore drift can fluctuate from day to day, and may vary locally as the beach tries to readjust its shape to be in better equilibrium with the waves and currents.