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.

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.

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.

Chesil and Fleet Birds

The Fleet lagoon’s mudflats provide an ideal feeding ground for many species of bird. During the winter the population swells, making this a favorite place to visit for bird watchers. The pebbles of the Chesil Bank alongside are an ideal nesting ground for Little Terns. These lay a single egg which is mottled in appearance, allowing it to blend in with the stones. The beach provides safety from predators such as foxes, dogs and cats, and is one of the few breeding strongholds for this bird to be found anywhere in the country.

Vegetated Shingle

Growing along the shore of the Fleet and on Chesil Bank are a multitude of plants, all especially adapted to growing in this harsh coastal environment. The plants are particularly prolific around Bum Point, the Fleet and Chesil Visitor Centre and they can also be found alongside the causeway beside Portland Harbour.

Ferry Bridge

The Isle of Portland only used to be connected to the mainland by the Chesil Bank. For years there was a ferry here dragged by a hawser attached to a capstan that was turned by a horse. “The Passage Boat” was replaced in 1839 by a timber bridge which was in turn replaced with an iron bridge in 1896. The current bridge is relatively modern, erected in 1985.