Longshore drift

Coastal erosion is in the news these days. Most spectacularly near Hayle in north Cornwall where geologist Richard Hocking caught an enormous fall on camera and, of course, like the modern equivalent of whether a falling tree makes any sound if there’s no one there to witness it, these things don’t really happen unless they are uploaded almost immediately to youtube. (It’s well worth a look though.) It goes without saying that the South West Coast Path has been diverted.

Technically speaking this erosion of the land is caused by the constant battering of the sea, primarily by the processes of hydraulic action, corrasion, attrition, and corrosion. Hydraulic action occurs when the force of the waves compresses air pockets in coastal rocks and cliffs. The air expands explosively, breaking the rocks apart. Rocks and pebbles flung by waves against the cliff face wear it away by the process of corrasion, or abrasion as it is also known. Chalk and limestone coasts are often broken down by corrosion and attrition is the process by which the eroded rock particles themselves are worn down, becoming smaller and more rounded. That’s cleared all that up then.

My staycationing this year has seemed to take me quite naturally to our picturesque coast, and particularly the south coast along the Solent. One more bright and sunny day of this Indian summer (I’ve often wondered about that phrase and apparently it’s a north American term dating from about 3 centuries ago: In the same way that Indian giver was coined for people who take back presents they have bestowed, the phrase Indian summer may simply have been a way of saying “false summer”. Well this year has been odd a scorching April and a blistering opening to October, I’ve never known anything like it) found us in Lymington.

They love their sailing down here – it’s got three marinas – and some TV programme rated it the best town on the coast but we were here to walk along the Solent Way along the edge of Pennington and Keyhaven marshes to Hurst Castle. The castle is one of Henry VIII’s coastal forts and was constructed at the end of a long shingle spit. It also has a picture perfect lighthouse. And it is long, about 2 kilometres I reckon, and every step is strength sapping, especially on the calf muscles. (So strength sapping that we took a ferry back to the shore rather than walk it again.) This is the beauty of shingle it can absorb huge forces and this beach was created by longshore drift.

OK pay attention here comes some more science. Longshore drift consists of the transportation of sediments (generally sand but also, as in this case, coarser sediments such as gravels) along a coast at an angle to the shoreline, which is dependent on prevailing wind direction, swash and backwash. (Swash as I’m sure you all know is a turbulent layer of water that washes up on the beach after an incoming wave has broken. Hence swashbuckling I guess.)

Spits are formed when longshore drift travels past a point where the dominant drift direction and shoreline do not veer in the same direction. As well as dominant drift direction, spits are affected by the strength of wave driven current, wave angle and the height of incoming waves. Spits are landforms that have two important features. The first feature being the region at the up-drift end or proximal end. The proximal end is constantly attached to land (unless breached) and may form a slight “barrier” between the sea and an estuary or lagoon. The second important spit feature is the down-drift end or distal end, which is detached from land and in some cases, may take a complex hook-shape or curve, due to the influence of varying wave directions. It’s on days like these I wish I’d paid more attention during geography.

The walk is splendid even if you don’t understand any of this and trust me at best I’ve got a very tenuous grip on it. You leave the chandler shops and marinas of Lymington behind you and you are quickly on the flat marshland with the whole walk spread out in front of you. It’s certainly big sky country round here and the landscape which at first appears deserted is actually teeming with wildlife. There’s oystercatchers, redshanks and what I think were curlews. All dipping, bobbing and wading their peaceful way through the pools and lagoons that surround you. The air is redolent with their gentle whistling and calling. The salinity in these lagoons varies widely, but is generally lower than seawater. This specialised habitat supports its own distinctive plants and animals, some of which are only found in this environment. The lagoons are some of the most important in Britain with populations of rare species including Foxtail Stonewort, Lagoon Shrimp and starlet Sea-anemone. On the walk back in the early evening we were accompanied by swooping sand martins who seem to revel in their ability to fly and for all the world just seem to be doing it because they’re simply having fun. And who can blame ‘em?