The Adur begins as two separate branches, the western Adur and the eastern Adur, which meet 2 km west of Henfield.

The western Adur rises at Slinfold from where it flows around Coolham and then through Shipley, where it meets Lancing Brook and flows on to West Grinstead and Knepp Castle.
 The western Adur is tidal as far north as Bines Bridge near Bines Green, south of West Grinstead.

The eastern Adur rises at Ditchling Common, in East Sussex, from where it crosses into West Sussex and meets Herrings Stream at Twineham (50.962746°N 0.235728°W).
At Shermanbury, the eastern Adur is fed by the Cowfold Stream.
The Normal Tidal Limit is just below this at the footbridge near Shermanbury Church although a weir just above the confluence with the Western Adur means that only the highest tides reach here.
Up to the early 1800s boats could navigate to Mock Bridge where the A281 crosses the Adur.

West of Henfield, the two branches of the river meet before flowing between Upper Beeding and Bramber, past Coombes, through a gap in the South Downs near Lancing College where the Adur is fed by the Ladywell Stream.
The river continues on to the English Channel at Shoreham-by-Sea.
The mouth of the Adur is now two miles (3 km) from the town centre of Shoreham due to longshore drift.
Previously, the river mouth was further east, in Portslade, but an opening to the sea was made which allowed the creation of Southwick Ship Canal.

The Baybridge Canal uses part of the Adur's watercourse.
The Adur begins as two separate branches, the western Adur and the eastern Adur, which meet 2 km west of Henfield.
The western Adur rises at Slinfold from where it flows around Coolham and then through Shipley, where it meets Lancing Brook and flows on to West Grinstead and Knepp Castle.  The western Adur is tidal as far north as Bines Bridge near Bines Green, south of West Grinstead.
The eastern Adur rises at Ditchling Common, in East Sussex, from where it crosses into West Sussex and meets Herrings Stream at Twineham (50.962746°N 0.235728°W). At Shermanbury, the eastern Adur is fed by the Cowfold Stream. The Normal Tidal Limit is just below this at the footbridge near Shermanbury Church although a weir just above the confluence with the Western Adur means that only the highest tides reach here. Up to the early 1800s boats could navigate to Mock Bridge where the A281 crosses the Adur.
West of Henfield, the two branches of the river meet before flowing between Upper Beeding and Bramber, past Coombes, through a gap in the South Downs near Lancing College where the Adur is fed by the Ladywell Stream. The river continues on to the English Channel at Shoreham-by-Sea. The mouth of the Adur is now two miles (3 km) from the town centre of Shoreham due to longshore drift. Previously, the river mouth was further east, in Portslade, but an opening to the sea was made which allowed the creation of Southwick Ship Canal.
The Baybridge Canal uses part of the Adur's watercourse.
River Adur