Friday, 28 August 2015

Seashell Coast - Pormpuraaw

One of the most remote towns in Australia is the Aboriginal Community of Pormpuraaw.  It is 210 km from the highway and approximately 500 km from the nearest town with more than 1000 people. The coast has a kind of desolate character that appeals to me.

Pormpuraaw foredune
Between the beach and the road is a grassland scattered with trees (Click photos to enlarge)
On arrival, I bought a pie and went down to be beach to eat it.  When I looked up, I found that I was being watched by no fewer than three medium to large crocodiles.  They were not sneaking up on me, rather I had just arrived where they sun on the beach near the river mouth.  Pormpuraaw has crocodiles up to five metres long and it is one place you do not want to take risks.

Estuarine crocodile
One of the crocodiles that was watching me
Pormpuraaw town is built on a couple of beach ridges made of sand and seashells and is wedged between an enormous salt pan and the sea.   Near the town is desert-like beach 8 km long and in many places the face of the beach is almost entirely seashells.  The shells are large and perfectly formed and it feels like a crime to walk on them.
Shells on Pormpuraaw Beach
The beach is at least half seashell, and the drifts are all shell
Close up of the seashell drift that runs across the middle of the photo above.
The sea is usually flat as Pormpuraaw is on the west coast of Cape York Peninsula and the prevailing trade winds blow offshore.  Pormpuraaw is in the Gulf of Carpentaria and this area has only one tide a day and has a reduced tidal range.  Actually, I am not totally sure, there are some places on the Australian coastline that do not have tide gauges and are hundreds of kilometres from a place that does.  The Gulf is also a bit strange.  Gove, which is one side of the Gulf has two almost equal tides each day and Port Musgrave, which is directly opposite has only a single tide each day.

Beach with a washed up sea fan in the foreground
Near Pormpuraaw, at low tide sand flats are exposed but they are flat and have neither the level of wildlife or the interesting patterns that I find elsewhere.   What is present are dead shells from two of the worlds largest molluscs, the bailer shell and the Australian Trumpet.  The shell of the largest Australian Trumpet ever found was about 91 cm long is actually the largest living shelled-gastropod.  However most of the trumpet shells at Pormpuraaw are about 20 cm long and few are in perfect condition.  Bailer shells were used for bailing boats, hence their name.  Broken shells of both species are common.

A small bailer shell
At either end of the Beach is a river and there are some huge crocodiles in these rivers.  I did not have a boat and took my photos just from the riverbank.  Mind you, I have a superzoom camera.  Would you believe that there were deep human footprints in the very soft mud along the waterline of the riverbank directly opposite where I photographed this crocodile!

Middle reaches of Chapman River, Pormpuraaw
Chapman River about 2 km from Pormpuraaw town
Sunbaking saltwater crocodile
5 metre crocodile on opposing river bank
If you go to Pormpuraaw, be sure to ring the Council first and make sure that their camping ground or guest house is open.   Allow about 3 days and be prepared to do something slow.  It has spectacular bird life, photogenic scenery and the locals are great.

Salt pan near road to Pormpuraaw

More about tides: I actually wanted to put in a tide gauge and be the first person to understand the local tide. Tides are the result of resonances between celestial bodies and the geometry of tidal basins and there are a large number of possible resonances.  I was surprised to find out that tides do not really flow in and out according the nice sinusoidal curve shown in tide charts.  There can be as many as six tides a day and an incoming or outgoing tide can reverse direction for a few minutes before resuming its original direction.  The observed tide is the result of several slow motion waves added together and these waves all move to different rules.  

To measure the tides, all that is needed is a self contained pressure gauge with integrated data logger.  Anchor it to the seabed in a sheltered location and collect at least two weeks of data.  Computer programs can then analyse the data and  make a tide chart.  I would probably like to collect more data as seiches may also occur in a place like the Gulf where the sea is shallow and strong winds blow.  This stuff actually matters.  In some harbours in Queensland, the amount of coal or ore that can be loaded into a ship is calculated according to what the tides are doing so as to maintain exactly 1 m clearance under the hull as the ship passes over the shallowest point.