Jncc coastal Directories Project Region 11 The Western Approaches

around the coastal plain estuaries, notably the Somerset
Levels, which stretch inland from Bridgwater Bay, and the
Gwent Levels along the northern shore of the Severn
Estuary.
4.1.2  Important locations and species
Map 4.1.1
shows the estuaries in the region and 
Table 4.1.2
summarises their main physical characteristics.  Estuaries in
the west of the region are mostly rias - non-glaciated river
valleys submerged by rising sea-levels; in the lower-lying
landscape further east are embayments and coastal plain
estuaries.  All the region’s estuaries are macrotidal (i.e. have
a spring tidal range >4 m).  Tidal range increases from west
to east in the region, in Cornwall being between 4.7 m
(Helford River) and 6.4 m (Gannel Estuary).  The Severn
Estuary, with a spring tidal range of over 12 m, has the
second largest tidal range in the world. 
On the south coast of Cornwall, on the rocky shores
around their mouths and in the sheltered soft sediments
further upstream, the rias of Falmouth and the Helford
River support important and diverse sea-bed communities,
including maerl and Zostera spp. (eelgrass) beds.  These
narrow, sinuous estuaries are predominantly subtidal, with
narrow strips of fringing tidal flats and saltmarshes,
especially in their upper reaches; much of the Helford River
is fringed by ancient woodlands.  On the north Cornwall
coast the small Hayle Estuary has formed behind sand spits
and has been much modified by human uses; further east,
the rias of the Gannel and Camel Estuaries have formed in
an otherwise cliffed and rocky coast.  Both Gannel and
Camel are shallow and predominantly sandy, but with
rocky areas near their mouths.  In north Devon the confluent
Taw-Torridge Estuary has formed behind the two sand spits
of Northam and Braunton Burrows, the latter in particular
being of major nature conservation importance as one of the
largest dune systems in Britain, with an extensive matrix of
grasslands and dune slacks.
On the Somerset coast Blue Anchor Bay is a broad area
of intertidal flats and shingle forming part of a series of
broad shore platforms, unusual in a macrotidal
environment.  Further east, the River Parrett discharges
across the broad tidal flats of Bridgwater Bay, a system
developed partly in the shelter of Brean Down and which
includes vegetated shingle banks and sand dunes with a
particularly rich flora.  The upper tidal reaches of the River
Parrett stretch into part of the extensive meadows and
marshes of the Somerset Levels; both the Levels and
Bridgwater Bay are internationally important for their
wintering waterfowl populations, and the Levels are
important also for breeding waterfowl.
North from Bridgwater Bay the vast coastal plain
estuary of the River Severn is of great importance for a wide
variety of features.  With its very large tidal range the
Severn Estuary provides an extreme example of a highly
turbid system.  Much of the outer part is subtidal, and in the
main estuary the intertidal flats are mostly highly mobile
sand; only in the shelter of side bays and estuaries such as
the Avon, Wye, Usk and Taff/Ely are there more stable
muds.  The estuary supports very diverse sea-bed
communities, especially on soft substrates but also on
intertidal rock platforms.  Large areas of mostly grazed
saltmarsh fringe the estuary and there are important wet
grassland areas around Slimbridge (Gloucestershire) and on
the Gwent Levels, the latter supporting a range of rare
aquatic invertebrates.  The Severn supports more species of
migratory fish (seven), including the allis and twaite shad
Alosa alosa and A. fallax, than any other UK estuary.  There
are large wintering waterfowl populations on the estuary,
including five species each occurring in internationally
important numbers.
Region 11  Chapter 4  Marine and estuarine environments
64
Table 4.1.2  
Physical characteristics of Region 11 estuaries
Estuary
Centre
Geomorph-
Total
Inter -
Salt-
Shoreline
Main 
Spring
Sub-
grid ref.
ological
area
tidal
marsh
length
channel
tidal
tidal
type
(ha
a
)
(ha
a
)
(ha
a
)
(km
a
)
(km
a
)
range (m)
%
Cornwall
154. Falmouth
SW8334
Ria
2,482
746
93
127
18
5.3
69.9
155. Helford River
SW7626
Ria
568
186
5
44
9
4.7
67.3
1. Hayle Estuary
SW5538
Bar-built
358
321
19
20
2
5.0
10.3
2. Gannel Estuary
SW8061
Ria
122
85
20
9
4
6.4
30.3
3. Camel Estuary
SW9375
Ria
839
610
50
43
15
5.9
27.3
Devon
4. Taw-Torridge Estuary
SS4631
Bar-built
2,463
2,018
240
88
21
7.3
18.1
Somerset
5. Blue Anchor Bay
ST0244
Embayment
350
350
0
9
0
9.7
0.0
6. Bridgwater Bay
ST2947
Embayment
6,529
5,147
487
109
46
11.1
21.2
Somerset, Avon, Glos., Gwent, S. Glamorgan
7. Severn Estuary
ST4080
Coastal plain
55,684
16,890
933
353
111
12.3
69.7
S. Glamorgan
8. Thaw Estuary
ST0366
Coastal plain
160
160
8
5
0
10.5
0.0
Mid Glamorgan
9. Ogmore Estuary
SS8776
Coastal plain
187
173
15
8
2
8.9
7.5
Sources: Buck (1993; in prep.); JNCC Integrated Coastal Database.  Key: 
a
areas/lengths rounded to the nearest whole hectare/kilometre.
Notes: estuary numbers are those used in Davidson et al. (1991).  ‘Geomorphological type’ relates to nine estuary categories, described
further in Chapter 5.7 of Davidson et al. (1991) and Chapter 4.5 of Davidson & Buck (in prep).  ‘Spring tidal ranges’ are for the monitoring
station closest to the mouth of the estuary.

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