Slapton Sands Shingle Ridge Breach, Start Bay, South Devon COASTS CS

UK coastal location and Primary Driver

• Location: Slapton Sands Shingle Ridge Breach, Start Bay, South Devon.

• Primary Driver: Bathymetry, wind, and a fixed sediment budget.

bathymetry: underwater shape, depth, and contours of the sea floor.

Why was Storm Emma's wind vector unusual?

• Storm Emma generated severe easterly winds exceeding 50+ knots across the English Channel.

• Slapton Sands normally faces dominant south-westerly Atlantic waves and is sheltered from the EAST by the headland, Start Point.

• The rare easterly storm vector exposed the coast to its maximum possible fetch.

How did offshore bathymetry focus wave energy?

• Offshore bathymetry in Start Bay features deep-water channels flanked by shallow sandbanks (e.g., the Skerries Bank).

• Easterly waves refracted over these seabed contours, concentrating energy directly onto the narrow central section of the Slapton Ley shingle barrier.

How did waves change the ridge during the breach?

• Destructive waves' backwash stripped the seaward face of the ridge.

• Overtopping waves pushed massive volumes of gravel inland over the crest.

• Pushed the entire ridge landward by several metres in hours.

Why is the sediment budget fixed?

• Slapton Ley is a relict shingle barrier formed during the Holocene transgression.

• The sub-sediment cell is closed with zero modern inputs (no new gravel from offshore or rivers).

• Because the sediment budget is fixed, every major storm event permanently thins the bar, increasing vulnerability to future storms.