The Borrow Dyke
Behind the sea wall is often a brackish pond, the borrow dyke.
The seawalls were built and raised long ago. They were made by digging out soil alongside the river banks and placing it along the edge of the tidal riverside to make the raised seawall or “dyke”. The wide trench or depression left by digging out the soil to make the seawall dyke is called a “borrow dyke”. The borrow dykes can fill with fresh water from brooks or groundwater, or sometimes they can fill with seawater which seeps through the seawall from the tidal river. They form a long linear body of water resembling a canal. Borrow dykes provide perfect habitats for all kinds flora, fauna and insects. The borrow dyke ditches, ponds and waters extend alongside nearly the entire seawall length and they provide an ideal shelter, home, paradise and food source for fish, eels, molluscs, micro-organisms, newts, frogs, toads, snakes, birds, mammals, insects, butterflies, moths, dragonflies, water plants, wild-flowers and grasses.
Saltings
On the seaward side of the sea walls a specialised habitat, the saltings can be seen, where there is enough shelter for the vegetation to develop. The plants of the saltings, such as Sea Purslane and Sea Lavender, are regularly covered by high tides so they are salt resistant and tough enough to stand a battering from the sea.
Between clumps of plants, there are many small pools and channels which become quite warm and very salty at low tide in the summer. The animal life of the saltings has to be tough enough to stand these conditions.
Mudflats
The estuary itself is the most obvious feature of south Essex. Its huge mudflats are feeding grounds for thousands of wildfowl and waders in the winter months, the most famous being the Brent Geese.
These handsome small near-black geese fly south to our coast from Russia and Scandinavia in autumn to overwinter on our coast before flying back to their northern breeding grounds in the spring.
Up to a tenth of the world's Brent Goose population arrives at the Essex coast where they feed on the eelgrass beds of the estuary mudflats.
They may often be seen flying between the feeding grounds of Foulness and Leigh in response to the changing tides. Large populations of wading birds feed on the invertebrates that live on and within the mud.
Sea walls and coastal grassland
The sea walls which protect fields from flooding by the sea are themselves interesting habitats while those fields behind the sea walls are examples of coastal grazing marsh.