Wedgies and Wide beaches

  The recent King Tides have contributed to some fore-dune erosion at Beach One, exacerbated by the wide and mostly flat beach summer berm profile.

Meanwhile at Point Smythe a pair of Wedge-tailed Eagles Aquila audax were observed patrolling at a very low altitude for birds with such keen eye-sight. Their sustenance consists predominantly of carrion, but rabbits, some marsupials and other birds can feature in their diet.
These two birds are more than 5+ years old, as attested by their dark colour. Younger birds are browner, progressively turning towards black as they age. In this photo the larger sized female is below her male.

So this is summer …

What is the saying? “Beautiful one day, overcast the next” …Welcome to Venus Bay 2012

This summer so far has not been the typical hot blazing sun and deep blue cloudless skies. yet on the beach there are signs that it has been a much more typical summer than the past few years (at least for the beach profile)

The Erosion at the top of the beach seems to be very limited (last big events being in November) and the scarps are drying and collapsing leaving a steep wedge of sand rather a vertical cliff (except where marram grass clumps are hold up some areas (as shown above). The Average Height Tide Line is 10 to 20 meters seaward from these scarps, which has meant that the flatten out upper part of the beach (the summer berm) has been able to be strongly developed along the beach. This an area where dried out seaweed and other beach debris can accumulate. the sand dries out and is more susceptible to wind erosion so this part of the beach is flatter.  This is an important habitat for the shore nesting birds (like the hooded plovers). Hopefully they are enjoying this summer on the beach.

BTW its the Walk out on Point Smythe TODAY!

Summer Berm

Despite the near tropical storms and downpours over the past fortnight, the summer berm is developing all along the beach at Venus Bay and only a few fresh erosion scarps can be seen. This upper beach is already flattening under mainly strong northerly winds and this brings promise of a wider summer berm this year. The full moon is tonight and it will be interesting just how high the overnight tide might reach.

Why is the summer berm returning?

Undeveloped ocean beaches like Venus Bay typically have a different shape in summer and winter. Normally in Australia these are called the Summer Berm and Winter Berm. At the moment you can see both shapes and we haven't seen a true wide summer berm develop along the beach for several years (possibly 2006/2007 was the last period).

So What is a Summer Berm?

The term Berm has a few different meanings, It can be a mound of earth set up to protect low lying areas behind it (a levy bank). It the USA it often is the name given to a beach or flat river bank or even the edge of road. Any sub level surface will be called a berm but the flat/horizontal part will be called a Bench , the change of slope called the Berm Crest and the sloping front face the Berm Slope.

During summer when the waves and swells are generally calmer the top part of the beach start to dry out and wind action starts to level out the beach changing its gradient and making it flatter. A surprising lot of sand can be moved bu the wind and often extra sand is "stolen" from lower wetter parts of the beach and builts up this top part of the beach. The first sign most of us will notice is a soft sand pile built up at the bottom of the ramp or steps down to the beach.

In winter, storms and pounding winter swells bringing a lot more wave energy to lift and redistribute the sand both on the beach and below the waterline. The shape is now a single gentle curve getting steeper up the beach. Whilst the winds can be stronger in these times the sand is generally very wet so less wind erosion in involved. The winter shape has dominated changes in the Venus Bay beach over the past few years.

I am beginning to suspect the return of the sumer berm is related to the general change to a northwards longshore drift.

It will be interesting to see if the hooded plovers and other shore birds have a more succesful breeding season with a wider upper beach and less risk of nests being washed away.

The new beach profile

Taken at 4:25pm (approx 2 hours before "official" low tide) on 11/1/2009 atmospheric pressure was 1012 hPa

The low tides at the moment seem exceptionally low for three reasons

1. The 18.6 year maximum tide cycle (its related to the full moon)

2. High atmospheric pressure ( lowers the sea level)

3. the beach profile has change. (little of no summer berm developed and lowering of the beach generally)


The above photo shows how different the beach profile is this year. The erosion scars at the back of the beach are "healing", the front faces have mainly collapsing and are forming a more even rill, The dry sand is being carried by the wind, eroding a smooth slope in some places and depositing and riling down in others. In front of this in only a few places a narrow summer berm is developing. This is the area mainly above high tide where the beach can dry out and wind erosion take over as the main erosion agent. The wind flattens out this zone to almost horizontal (which is why it is called a berm) When it develops a distinct bump can be seen, where the gradient of the beach changes. In previous years this summer berm may have reach 10-30m wide by mid January. Now it is only present in a few places and seldom wider than 3m. The beach in front of that still have the steep gradient more characteristic of winter and the old beach profile has been clearly lowered (much sand eroded away). In front of that there are extensive flatter areas of sandbank being developed. This sand is frequently soft (unconsolidated) because it is being moved back and forth a lot with each tide). Extensive rutting, guttering and ripple pools are being developed and then wash away in the next tide or their position and form changing daily. The beach is reaching width of 100m to 150m from dune to water edge at low tide.