Adur Mouth, Shoreham

Changes in the mouth of the Adur at Shoreham

The mouth of the River Adur has been greatly affected by the drifting of shoals of sand and gravel from west to east, and by major attempts by man to maintain it as a usable harbour. The original port on the estuary of the Adur was at Old Shoreham 1.5km north of the present coastline near the old church of Old Shoreham, and the river was navigable up to Bramber (1). By the eleventh century, silting of the river resulted in the port being moved 1km downstream to what is now the town of Shoreham but was then called New Shoreham (2). Silting continued to affect the port as a result of an eastward growing spit across the estuary mouth.
At the time of the Armada Survey in 1587 (Fig 4a) the river ran eastwards from New Shoreham for a distance of about 1km to discharge at a point between New Shoreham and Kingston-by-Sea. The coast west of the mouth was fronted by a shingle beach which attained a width of 1km opposite New Shoreham, tapering away towards Lancing. Behind the beach, and along the line of the original coast was a depression occupied by an arm of water flowing into the river and directly across the river from New Shoreham there were a series of lagoons. Large sand banks lay in the mouth of the Arun which must have hampered entrance and exit by boats.


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Bleau, in 1648, records a very noticeable extension to the Shoreham beach spit of 1.4km giving a total spit length of 2.4km. In 1698 Dummer's map (Fig 41b) shows a further 600m of shingle having built up with extensive shoaling in the estuary beach mouth and the formation of many bars within the river. The eastward extension of Shoreham beach appears to be accompanied by its thinning from a maximum width of 1km in 1587 to less than half a kilometre in 1698 while the backwaters across the river from New Shoreham appear to have silted up and become marshland.
Between 1698 and 1760, an artificial cut appears to have made through the spit opposite New Shoreham (3) but the cut only survived or a short time. In 1724, the river discharged at Portslade 4.7km east of New Shoreham, and, in 1757, it discharged at Aldrington, 5.1km from New Shoreham (after maps by Budgen and Lt. Roy resepctively). In 1760 it was decided to make an artificial cut at Kingston (4) to shorten the exit to the sea, thereby improving access to the port and improving drainage upstream. This had the effect of overwhelming the saltings on the north bank due to the increased tidal flow (5). The Yeakell and Gardner map of 1778-83, (Fig 4c), shows a belt of marsh protected by the shingle bar to the east of the exit which is wider than the present day bar. In contrast, the shingle forming the western arm is narrower than it is today, especially opposite Shoreham where mud banks lie within the channel. As a result of the continued drift of shingle across the 1760 cut (6) temporary openings were made opposite Southwick in 1775 and 1800. Yeakell and Gardner's map shows how the 1775 cut was diverted 450m eastwards in the few years up to the production of that map. By 1815 the harbour mouth was 2km east of Kingston, and in 1818 the 1760 opening was re-opened with the protection of groynes and breakwaters (7). Greenwood, 1825, shows the new 1818 cut and the earlier abandoned cut 2km to the east (Fig 4 d). In 1821 harbour works were built to make the 1818 cut a permanent opening (8) and in the 1850s the former channel east of Kingston was converted into a canalised, lock controlled basin (9).
Since 1816 changes in the basic estuary shape have been negligible although the various Ordnance Survey maps from 1874 indicate that there have been minor changes within the harbour estuary in terms of shifting mud and sand banks (Fig 4e). However, the shingle which makes up the two arms of the spit has been less stable. The western arm, aided by groynes has experienced a gain in material, and has been judged sufficiently stable for housing development to be permitted. In contrast, on the eastern arm despite groyning the reserves of shingle have slowly been depleted causing concern about the safety and stability of Shoreham power station, now disused and soon to be demolished (Fig 4f)
NOTES.
1. Steers, J.A. 1964:- The Coastline of England and Wales.- Cambridge pp 306-308.
2. Robinson, D.A. and Williams, R.B.G. 1983: The Sussex Coast Past and Present.- Sussex; Environment, Landscape and Society.- The Geographical Editorial Committee. University of Sussex (ed), Alan Sutton, chapter 3 pp 44-55.
3. Steers, op. cit.
4. Robinson and Williams, 01). cit.
5. Brookfield, H.C. 1952: The Estuary of the Adur.- Sussex Archeological Collections.- Vol 90 pp 153-163.
6. Steers, op. cit.
7. Brookfiels, op. cit.
8. Steers, op. cit.
9. Robinson and Williams, op. cit.