Fleet Peat

Peat deposits washed onto the Chesil Bank from the old Fleet Lagoon floor on the seaward side of Chesil Beach indicate the lagoon was once much bigger. The lagoon is currently shrinking at the rate of around 5cm every year as the Chesil Beach marches slowly inland.

The Fleet Lagoon

The Fleet Lagoon formed during the last Ice Age. It covers an area of 480 hectares and varies in width from 50 meters to over 910 meters. At its deepest it is 4 meters, with many areas much shallower, around 0.5 meter. Some of the lagoon floor is exposed at low tide.

Pebble Size and Longshore Drift

The stones that make up the Chesil Beach are mainly derived from East Devon, consisting of Metaquartzites of the Ordovian and Devonian Age, Chert and Flint. A unique feature the Chesil Beach is how the pebble size changes from one end to the other. Large cobbles are found at Chesil Cove, Portland, while West Bay has fine grit and gravel. It is thought the bigger heavier stones have a larger surface area and are therefore carried further to the east by the powerful prevailing south westerly waves hitting the beach at an angle, while the smaller lighter stones are carried back to the west by the less powerful waves approaching from the south east. In effect the stones zigzag their way along the coastline, carried by this longshore drift, accounting for the size graduation. The harbours at Lyme Regis and West Bay are both obstacles to the longshore drift, and the reduction in quantity of stone being delivered through coastal erosion in East Devon is diminishing. The long-term future

The Chesil Beach (Chesil Bank)

Consisting of a 100 million ton bank of pebbles, the Chesil Beach stretches for 28 km to West Bay. The beach varies between 36 and 200 meters wide and also in height, being 14 meters at Portland and just 5 meters at West Bay. The bank of pebbles separates the sea from Britain’s largest tidal lagoon, the Fleet, an important wildlife habitat for all manner of extraordinary flora and fauna. The beach is marching inland at a rate of 5 meters every century, reducing the size of the Fleet Lagoon in the process. The Chesil Beach is by no means stable. Storm waves have breached its pebble bank several times in the past, flooding the Fleet Lagoon, the land behind it and Portland to a depth of several meters. In one great storm the beach was swept away, exposing the underlying Kimmeridge Clay, in which were coins, jewelry and all sorts of artifacts that had been lost between the pebbles throughout the centuries.

Tidal Link Channel Marine Habitat

The constriction of the Fleet Lagoon’s tidal link channel at The Narrows forces the water to rush to and from Portland Harbour at tremendous speed. Where the lagoon is wider to the west, the tide is less strong, allowing sediments to fall from the water, creating the muddy seabed associated with the eelgrass that lives in the shallows. By contrast, the 4 meter deep seabed of The Narrows is swept clean and consists of gravel from the Chesil Bank. This is why the marine life living here varies so differently from that found in the shallower, wider parts of the Fleet Lagoon.

The Chesil Beach and Smugglers

Folklore says that a local fisherman or smuggler could tell exactly where he was on the beach at night or in fog simply by looking at the size of the pebbles. This aided him in sneaking ashore, away from the customs men and their patrols.