50°N

55°N

B

CGreat

Britain

5°W 0°

100 km

Fig. 1. Position of Ramalhete (A) in Portugal,and East Chidham (B) and Freiston Shore (C) inEngland.

100 km

A

Po

rt

ug

al

S p a i n

8°W 6°W

40°N

36°N

a b

c d

Fig. 2. Illustrations of studied salt-marsh vegetation. (a) at Ramalhete; canopyheight is 30 cm. (b) in front of a red background, example of picture used to computethe lateral obstruction; picture height is 34 cm; picture depth is 10 cm. (c) marsh at EastChidham. (d) Low pioneer marsh with . and at Freiston Shore; length ofyellow ruler is 8 cm.

Spartina maritimaSpartina anglica

SpartinaSalicornia sp Suaeda maritima

Location GFreiston Shore

England

Salicornia sp.Sueda maritima

Heig

htabove

bed

(cm

)

0%0

20

Heig

htabove

bed

(cm

)

Lateralobstruction

50% 0 5

G10 (42cm)

0 5

G18 (17cm)

0 5 10

G5 (38cm)

0 5 10

G6 (40cm)

0 5 10

G12 (38cm)

0

20

0 5 10 15

G3 (26cm)

Location F

East ChidhamEngland

Spartinaanglica

Heig

htabove

bed

(cm

)

0%0

20

Heig

htabove

bed

(cm

)

Lateralobstruction

50%0

20

40

60

80

0 5

F10 (112cm)

0 5

F11 (115cm)

0 5

F12 (115cm)

0 5 10

F14 (106cm)

0 5 10

F18 (78cm)

0 5

F29 (20cm)

Location E

East ChidhamEngland

Spartinaanglica

0%0

20

Heig

htabove

bed

(cm

)

Lateralobstruction

50%

Heig

htabove

bed

(cm

)

0 5 0 5

E9 (91cm)

0

20

40

60

0 5

E1 (28cm)

0 5

E3 (44cm) E6 (71cm)

0 5

E15 (62cm)

0 5 10

E13 (79cm)

0 50 100 1500

20

Heig

htabove

bed

(cm

)

Location C

RamalhetePortugal

Spartinamaritima

Biomassdistribution

Heig

htabove

bed

(cm

)

g m layer-2 -10 5

C11 (74cm)

0

20

40

0 5

C4 (45cm)

0 5

C8 (69cm)

0 5

C9 (75cm)

0 5

C13 (63cm)

0 5 10

C6 (60cm)

Location B

RamalhetePortugal

Spartinamaritima

Heig

htabove

bed

(cm

)0 50 100 150

0

20

Biomassdistribution

Heig

htabove

bed

(cm

)

0 5 10

B12 (69cm)

0

20

40

0 5

B1 (30cm)

0 5

B2 (39cm)

0 5

B10 (74cm)

0 5 10

B4 (54cm)

0 5 10

B7 (70cm)

Location H

FreistonShore

England

Spartinaanglica

Heig

htabove

bed

(cm

)

0 50 1000

20

40

Heig

htabove

bed

(cm

)

Biomassdistribution

0%

Lateralobstruction

50% 0 5

H15 (55cm)

0 5

H19 (18cm)

0

20

40

60

0 5

H1 (24cm)

0 5 10

H3 (40cm)

0 5 10 15

H8 (76cm) H10 (84cm)

0 5 10 15

g m layer-2 -1

Location I

FreistonShore

England

Spartinaanglica

Heig

htabove

bed

(cm

)

0 50 1000

20

40

Heig

htabove

bed

(cm

) Biomassdistribution

0%

Lateralobstruction

50%0

20

40

60

0 5

I 1 (19cm)

0 5

I 2 (28cm)

0 5

I 14 (69cm)

0 5

I 18 (39cm)

0 5

I 20 (25cm)

0 5 10

I 4 (57cm)

0 5 10

I 7 (79cm)

Mean horizontal velocity (cm s ) with standard deviation-1

Fig. 3. Selection of profiles of mean horizontal velocity with i (or downstream standard deviation)

presented as the error bars. Each velocity profile is labelled with its profile name (e.g., "B1") and, inbrackets, the water depth during measurements. The vertical density variation of the canopy isrepresented on the left hand side by the vertical biomass distribution and/or by the lateral obstruction ofa 10 cm thick canopy.

u

z (cm)visual

z(c

m)

0

0

10

20

0 10 20 30

z = 0.8374 z – 1.1617

R = 0.8773

p < 0.01

0 visual

2

·

Fig. 4. Relationship between z (lower limit of

the skimming flow defined visually from theplots) and z for all profiles with a

skimming flow exhibiting a logarithmicvelocity profile. The statistically significantlinear regression is shown.

visual

0 Spartina

cm s-1 J m-3 Pa

U with iu � �xz xyz&TKE & TKEhoriz vert U with iu � �xz xyz&TKE & TKEhoriz vert

H17

0

20

0 105 0 0.2

H20

H9

G2

G5

G9

0

10

0

20

40

60

0

20

0

20

0

20

0

0

0

0

0

10

20

20

10

10

5

10

10

5

5

0 0.1

0 1 2

0 0.5 1

0 0.5 1

0 0.5

heig

htabove

the

bed

(cm

)

0 0.01

�xz

�xyz

TKEhoriz

TKEvert

3

0 0.02-0.02

0 0.2

0 0.1

0 0.05

0 0.2

B1

B9

E10

F17

0

20

40

60

0

10

0

20

40

60

0

20

40

60

0

0

0

0

10

10

10

10

5

5

5

5

0 0.4 0 0.2

0 0.4 0 0.4

0 0.2 0 0.04

0 1 0 0.2

cm s-1 J m-3 Pa

heig

htabove

the

bed

(cm

)

Fig. 5. Profiles of flow parameters: Mean horizontal velocity (U) with i (or downstream standard

deviation) represented by the error bars, horizontal and vertical TKE, two dimensional and three

dimensional Reynolds stresses ( and ). The horizontal dotted lines mark the top of the dense

canopy and the canopy height, respectively. Profiles B1 and B9 are in a marsh;profiles E10, F17, H17, H20, and H9 are in a marsh; profiles G2, G5, and G9 are in a

marsh.

u

xz xyz� �

Spartina maritimaSpartina anglica

Salicornia / Suaeda maritima

Fig. 6. Ebb flow during experiment H ( , 32 cm tall):5 successive velocity profiles (mean U) with the correspondingprofiles of turbulent kinetic energy (TKE). On the right hand sideare shown the time in minutes after high water, the height of thewater level, and the significant wave height (H ). The flow

accelerated as the water level dropped, the associated reduction inTKE is probably not due to the velocity increase but the decrease ofsurface wavelets (shown by H ).

Spartina anglica

m0

m0

Heig

htabove

the

bed

(cm

)

0 0.5 1.0

J m-3

TKE

0

10

20

30

40

0 2 4 6

cm s-1

+51' 55cm 1.9cm

+63' 41cm 1.5cm

+67' 34cm 1.0cm

+76' 22cm 0.4cm

+83' 14cm 0.1cm

Time Water Hlevel

m0mean U

Heig

htabove

bed

(cm

)H

eig

htabove

bed

(cm

)

SSC (mg/l)

0

20

40

60

0

0

0

10

10 20

20

20 30 40 60

0

20

40

60

0 10 20 30

(A) -38 min. (B) +1 min.

(B) +35 min. (D) +53 min.

Fig. 7. SSC profiles measured in the salt-marsh at Freiston Shore during experiment H.The dotted horizontal line marks the canopyheight. The time before/after high water isspecified for each profile. The width of themarkers indicates the accuracy of eachmeasurement.