LONGSHORE DRIFT
INFORMATION SHEET
THE BEACHES
ARE ON
THE MOVE!
NRA
N a tio n a l R ivers A u th o r ity
S o u th e r n R eg io n
G u ard ian s of
the W ater Environm ent
Shingle beaches are an important
part of our sea defences in Southern
Region, they act as a cushion against
the pounding waves
...BUTTHEYAREONTHEMOVE!
o.
SINGLE TICKET, CHRISTCHURCH TO DOVER
The san d and broken ston es for ou r beaches cam e from the continental sh elf
w hen the last ice-age finished. G round up sea shells and flints from eroded chalk
cliffs have ad d ed m ore beach material since.
Over the centuries, becau se the w ind and w aves usually com e from the SouthWest, the shingle has m oved along the coast tow ards the East. It d oes not take
many days o f w atching to see that the stones are still on the move. At Dungeness,
for exam ple, the sh oreline westward o f the point is eroding at a rate o f about 2
m etres per year, w hile to the North the beach tends to accrete or build tow ards
France.
THE ZIG-ZAG ROUTE
WAVES APPROACHING AT AN ANGLE
The reason for all the movement is called longshore drift.
Let us follow the cou rse o f one pebble. A wave under the influence o f the w inds,
ap p roach es the coast at an angle. As the wave breaks, it carries the pebble up the
beach w ith its forw ard movement o r swash' (1). The backw ash’ o f the wave
trick les straight dow n the beach and the pebble rolls with it (2).
The pebble is now at position 3 and ready to be moved forw ard again by another
wave.
And so with all the oth er pebbles.
There are.several things that affect longshore drift — especially the num ber o f
days in a year that w inds com e from one direction; the strength o f the w inds, and
the ‘fetch’ or distance that the waves have had to travel in which to build up their
height and power.
RIVERS IN PERIL
Along the South coast, longshore drift is generally from West to East. This has tw o
im portant effects; first that the stones tend to be m oved away from the western
end o f the beaches, and second that the pebbles pushed along the coast threaten
to close o ff the entrances o f rivers. This is where the National Rivers Authority
intervenes. Shingle tending to obstruct the mouth o f rivers is picked up and
This gives three benefits — sea defences are protected, the river can discharge
freely and the entrance is left open for shipping. Each year costly replacem ent
and m aintenance is undertaken on our beaches. A cushion o f shingle must be
preserved and in som e cases reinstated, to dissipate the energy o f the storm waves.
West o f D ungeness and in other vulnerable areas, protection
has been achieved by renourishing the beach with
transported shingle — a continuous picking up o f shingle
from beyond the point and transporting it back to the West '
to continue its function as part o f the longshore drift along
the foreshore. In a m ajor civil engineering operation, which
was the largest o f its kind in the country, an artificial beach
nourishm ent schem e has been com pleted at Seaford at a cost
o f £13 million.
!
E n v ir o n m e n t A g e n c y
WORKING WITH THE SEA
The National Rivers Authority know s that our beaches need as much attention as
ou r countryside. By w orking with the sea, it w ill ensure that the protective
shingle is spread evenly along the Channel coast to protect people and property
from flooding.
NATIONAL LIBRARY &
INFORMATION SERVICE
SOUTHERN REGION
Guildbourne House. Chatsworth Road.
Worthing, West Sussex BN 111 LD
LOST HARBOURS
S A N D W IC H
— o n c e a m a jo r port an d naval base, now 2 km
in lan d , em b alm e d in san d . L o n gsh o re drift created a spit running
n o rth w ard from D eal w hich fo rced the Stour River into a hairpin
b e n d . T h e last straw w as the w re ck in g o f a large sh ip b elon gin g to
the P o pe in the en tran ce to the Stour in the mid sixteen th century.
Sh e trap p e d the san d an d created a d an g e ro u s bar.
HYTHE.
A round the year 1,000, the R iver Rother entered the sea
n ear H ythe w hich w as an o th er o f the C in q u e Ports But w ithin 300
y ears the sh in gle d rifted a lo n g the sh o re o f the Rom ney Marsh and
e x tin g u ish e d the entrance.
ROMNEY
w as the next exit to the se a that the River Rother
a d o p te d . A su c c e ssio n o f sto rm s an d flo o d s savaged northw estern
E u ro p e d u rin g the thirteenth century. A great storm in 1287
c a p tu re d the R other an d drew it w estw ard to Rye.
RYE' S
b attle to k eep o p e n is still g o in g on . To reach the tow n now,
b o a ts have to g o 4 km up the Rother. A c astle built in 1539 b eside
the a p p ro a c h e s to Rye is now m ore than a kilom etre inland.
OLD W IN CH ELSE A
sto o d on the sh in gle to the West o f the
m o u th o f the Rother. In 1250 a sto rm , c o m b in ed w ith high tides,
b re ac h e d the sea d e fe n c e s. T h e great sto rm o f 1287 destroyed the
to w n an d its rubble ro lled aw ay to join the rest o f the shingle on
D u n g e n e ss.
PEVENSEY HARBOUR
w as on ce situated on a lagoon
behind the shingle spits o f the coastline and Pcvensey C astle could
be reached by ships at high tide. The eastw ard drift choked the
mouths o f the stream s and the lagoon silted up. encouragin g man to
recover the m arshland for farming.
SEAFORD AND LEWES.
The O use’s losing battle against
the shingle and silt resulted in the dow nfall o f both ports. In Roman
tim es the river cam e out roughly w here it d o es now. Then the
longshore drift threw a shingle spit across the river and m oved it
4 km. The haven o f Seaford grew up there but the new river mouth
w as threatened by the driftin g shingle. A man-made cut w as m ade to
save the river and took it by a direct route to the sea where a New
Haven was founded.
PEN-HOUSE IN LANCING.
Until the latter half o f the
fifteenth century the Adur and the Arun shared a com m on entrance
to the sea just East o f Lancing Church. Shingle pushed the Adur
towards Hove an d the Arun w as thrust back w estw ards. Fresh exits
form ed at W orthing, G oring and Ferring. Around 1500-1530 it
b roke through near Littleham pton. Shoreham Beach is a spit o f
shingle created by longshore drift w hich turned the mouth o f the
Adur eastwards.
SELSEY
w as form erly an island. The gap was closed by longshore
drift leaving on ly the vanishing harbour o f Pagham on the eastern
side. Once a m ajor Roman Fort, Selscy, together with its cathedral
w as washed aw ay by the sea.
An exam ple o f how
m uch the coastline
has altered over the
centuries in one
part o f our region.
REFERENCES
Murray, J.C . (1953). Rom ney M arsh. Robert Hale Ltd.
C ald er, N. (1986). T h e English C h an n el. C h atto & . W indus Ltd.
R o b in so n , G.W. (1972). Land D rain age an d Sea D efence o f Romney
M arsh. C antium .
Roper, A. (1972). R om ney M arsh — T h e Fifth Quarter. Cantium .
Sm y th , C. an d Je n n in g s, S. (1988). C o a stlin e C h an ges and Land
M an agem en t in East S u sse x , Sou th ern E ngland. O cean and
Shoreline Management II, 375-394.
* Robinson, G. (1984). Land D rainage and Sea Defence o f Romney
Marsh. Gazette o f the A ssociation o f Drainage Authorities, 65-74.
* Holm es, A.E. (1988). The Seaford Sea Defence Scheme. IWFM
Conference, 16.1-16.13.
'
A v a ila b le on req u est fr o n t S K A So u th ern Region.
NRA
N a t io n a l R ivers A u th o r ity
S o u th e r n R e g io n
G u a rd ia n s of
the W ater Environm ent
Guildbourne House, Chotsworth Road, Worthing, West Sussex BN11 11D Telephone: (0903) 820692
June 1 9 9 3