Longshore drift on this coast runs west to east and everything about the beach obeys it. One stretch between two groynes builds up on the wrong side, by about eleven cubic metres a month, every month since 2014.
I am a coastal monitoring officer. Twice a year, and after every big storm, I survey beach profiles along about nine miles of frontage.
A profile is a line perpendicular to the shore. You start from a fixed marker with a known position, and you walk out to the low water mark taking heights, which is done with a GPS on a pole now and used to be done with a level and a staff.
Do that twice and subtract, and you have how much sand arrived or left, per metre of frontage, in cubic metres. That number is the whole of coastal management: it decides where the groynes go, whether a beach gets recharged, and whether a road behind it has ten years or thirty.
There are forty one profile lines on my frontage and I have surveyed all of them since 2011.
Longshore drift here is west to east. It is not in doubt.
You can see it without instruments. Every groyne on this coast has sand piled against its western face and a step down on the eastern side, sometimes a metre and a half of step, and that is the single most obvious fact about this beach.
The sediment modelling says the same, the historical maps say the same, and the reason the harbour at the eastern end dredges every year and the one at the western end does not is the same.
Profile 23 is between two groynes about four hundred metres apart.
The forty metres immediately east of the western groyne gains sand.
That is the wrong side. Sand piles on the WEST face of a groyne, which is upstream. The east side is the starved side. It is the side that gets a scour hollow.
Profile 23 gains about eleven cubic metres per metre of frontage per year, which over that forty metre stretch is a lot of sand, and it has done every year since 2014.
What has been checked, by me and by two consultancies who were paid.
The survey. Repeated by a second officer with a different GPS. Same answer. Repeated by a contractor with a drone and photogrammetry in 2019, which is a completely different method, and their surface agrees with my profiles to within a few centimetres.
The groyne. Inspected by a structural engineer in 2018 because a groyne with a hole in it can pass sand through and do odd things locally. It is a timber groyne in good condition with no gaps below the sand line, and they excavated to check.
Whether the drift reverses there. This is the intelligent answer and it is what the first consultancy went looking for. A headland or an offshore bank can set up a local eddy that runs the other way, and then a small stretch of beach genuinely does drift east to west.
There is no headland and no bank. They put in a wave buoy and current meters for eleven months and the answer is that the nearshore current at profile 23 runs west to east, at the same speed as everywhere else, all year.
Their report says the accretion is not consistent with the measured hydrodynamics and recommends further monitoring. That is a phrase that means nobody knows.
Where the sand comes from.
This is the arithmetic that made me start keeping a separate file at home.
If sand is arriving at profile 23, it is leaving somewhere else. That is the one thing sediment must do: the budget balances or somebody is measuring wrong.
I have the whole frontage. Forty one profiles, fourteen years.
The budget balances without profile 23. Every other line on this coast behaves, and the totals in and out at the ends of the frontage match the models within the error you would expect.
Profile 23's eleven cubic metres a year is extra. It is not coming from the beach either side, which has been checked at ten metre spacing, and it is not coming from offshore, because the nearshore bathymetry has been surveyed three times and is stable.
The sand itself.
In 2021 the second consultancy did what I would have done years earlier if I had thought of it, which is take samples and look at them.
Beach sand has a signature: grain size distribution, roundness, and the mineral content, which tells you what rock it came off and therefore where.
Profile 23's sand is not this coast's sand.
It is coarser. It has a different heavy mineral fraction. Their report says it is consistent with a source in a formation that outcrops about sixty miles north west of here, and that it is unlikely to have been transported by the modern regime.
The words in the report are unlikely to have been transported. Not impossible. Nothing in this field is ever impossible.
Sixty miles north west, up the coast, past two headlands and an estuary mouth.
I looked at what is there, which took an afternoon.
There is a cliff of that formation and there is a village at the bottom of it, and the village lost about thirty metres of frontage between 1953 and 1978 and the sea wall went in after that.
I am not going to draw a line between those two things. Sand from a lost frontage does not travel sixty miles the wrong way up a coast and stack itself against the wrong face of a groyne at eleven cubic metres a year.
I am aware that I have written the two facts next to each other, which is its own kind of drawing a line.
What I do about it professionally.
Profile 23 goes in the report with everything else. Accretion is not a hazard: a beach that gains sand protects the land behind it and my job is the land behind it.
The council's shoreline management plan has that stretch down as no active intervention, which is the correct policy for a beach that is looking after itself, and it will stay that way for as long as the numbers look like this.
What I do unprofessionally is walk it, twice a year, in the week after the survey.
There is a step down on the eastern side of that groyne now, which took eleven years to build, and it is about a metre and a quarter, and you have to jump it.
I have started going round it, up onto the promenade and back down the ramp, which adds ninety seconds and which I could not explain to the second officer if he ever came with me, except that he has stopped coming with me, and I have not asked why.