Tuesday, October 3, 2023

Conditions ideal for a spectacular opening

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John Xanthis, Wilson Inlet Restoration Group, Denmark Bulletin

In ideal conditions Wilson Inlet spectacularly opened on June 29 at 1.26 AHD, 100m from the western cliffs. Water levels in May were at -.2 AHD, with a dry winter forecast predicted.

Consistent rain started in early June.

Wilson Inlet Restoration Group’s mapping had shown more sand in the delta than a normal year and a sand spit in Prawn Rock Channel stranding our pontoon bridge.

The sand bar opening had a quick release of water from high to low with a high pressure system for four run out days, a north-east wind, small swell and four 1.4m tides after the opening.

This scoured our sand bar and serviced our channels and placed the sand bar out in front of the mouth.

When water levels finally dropped, a low-pressure system moved in.

The front caused a swell and storm surge that brought in a blue tidal exchange. With back up rain falling, it seemed that all the planets had aligned for a very serviceable sand bar opening.

Previously high water level sand bar openings have resulted in long duration openings with seasonal variation.

The value of having the inlet opened in winter is plain to see after the last couple of years for water exchange.

Monitoring for the impact of the sand bar that is put out in front of the inlet after sand bar opening is needed to get a clearer picture for water exchange.

There is a perception that the sand bar opening is responsible for the erosion in front of the surf club at Ocean Beach.

All beaches experience erosion in winter with big swells, tides, low pressure systems, storm surges and a rising sea level.

The four non-sand bar openings since 2007 and the two eastern openings in 1990-91 also, unfortunately, eroded Ocean Beach away in front of the surf club in winter.

Historically, the beach comes back in summer when the south easterlies blow.  

Denmark Bulletin 20 July 2023

This article appeared in the Denmark Bulletin, 20 July 2023.


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