The River Adur

The River Adur Corridor
Map of River Adur catchment

The River Adur is one of the four main rivers that drain the county of Sussex.  Going upstream from its estuary at Shoreham by Sea, the river is tidal and is contained within man-made embankments for a distance of some 9 miles through the ‘Shoreham gap’ in the South Downs until it gets to a fork just west of Henfield.  The embankments  continue for a short distance up each of the two arms, until the river becomes non tidal – at Shermanbury on the east arm, and Bines Bridge on the west.  Both arms are fed by many tributaries and ditches. However the nominal sources for each are defined as Ditchling Common in the east, and Slinfold in the west.

Catchment geology

Like all rivers, the geology of the catchment determines the river’s characteristics.  More than half of the catchment geology is relatively impermeable Gault and Weald clay, thus making the flow of these portions of the river closely related to rain that has fallen in the preceding hours.  The remainder is fed from water that is released more slowly from springs in the sand strata and chalk which make up the rest of the catchment.

The eastern arm of the middle Adur near Shermanbury

The eastern arm of the middle Adur near Shermanbury

 

The alluvial flood plain has artificial embankments which now prevent the river’s natural tendency to flood following high rain fall.  However, the portion of the river downstream from the A27 flyover, and upstream from the Shoreham town footbridge, does still have salt mud flats which are fully tidal.

View of the tidal Adur from Mill Hill Shoreham

View of the tidal Adur from Mill Hill Shoreham

Thousands of years ago (but less than 10,000) the river used to be much bigger when it drained the melt waters from the receding icecap north of London.  Even in the last few hundred years, its course has changed significantly.  Until the latter half of the 15th Century, the river shared a common estuary with the Arun at Lancing.  Sea going ships used to be able to go upstream as far as Steyning.

Today, sea going ships – admittedly much bigger – stop short of the foot bridge in Shoreham.  However the majority of ships using Shoreham now use the eastern arm of the harbour which is locked.

Redshank Tringa totanus feeding on the mudflats

Redshank Tringa totanus feeding on the mudflats

Mock Bridge on the eastern arm of the Adur

Mock Bridge on the eastern arm of the Adur

Natural History

The mud flats, at medium to low tide, are populated by gulls and other birds.  Waders and other birds on the mud include Dunlin, Redshank, and Lapwing, which return to the mud having nested inland during the Summer. Boats and wooden posts are occupied by Cormorants fanning their wings after feeding on eels and other fish.  In the summer, Terns also perch on wooden posts before taking off, climbing, and carrying out their characteristic dive onto their prey. Sometimes a whole flock of Turnstones can be seen on the gunwhale of a moored boat, having been forced to abandon the shore line by the rising tide.

The fish population includes Tench, Bream, Carp, Chub, Roach and Rudd.  Sea Trout are found on their way to and from the headstreams where they spawn in the winter.  They present a spectacular sight as they negotiate weirs and other obstacles.  Flounders, Eels, Grey Mullet, Sand Smelt and Bass are present in the estuary during summer and autumn.






Jim the Fish

Jim's Diary

Country ramblings from OART field officer Jim Smith





Rivers Gallery

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