RESTORING ECOSYSTEM FUNCTIONS IN A HEAVILY DISTURBED ESTUARY

Tom Maris, Stijn Temmerman & Patrick Meire

Driving forces: - Dredging & embankments- Pollution- Climate change

loss of ecosystem functionsImpact on:- safety- economy- ecology

Schelde: disturbed estuary

Structure

Fu

nct

ion

35853

42341

28,4

20,3

32000

34000

36000

38000

40000

42000

44000

1900 1990

Su

rfac

e (h

a)

0

5

10

15

20

25

30

% i

nte

rtid

al a

rea

total surface % intertidal

Schelde: disturbed estuary

Loss of intertidal habitat loss of goods and services

5.0

5.5

6.0

6.5

7.0

7.5

8.0

1930 1950 1970 1990

ann

ual

max

. HW

(m

TA

W)

Schelde: disturbed estuary

Increasing tides: risk for floodings

slope , current speed marsh erosion

Increasing tides: habitat loss

Schelde: disturbed estuary

Structure

Fu

nct

ion

Return to pristine situationis impossible.

Sustainable solutions:

Restoring functions

Managed realignment? - Elevation often not suitable - Not always compatible with safetyplan

Flood control area: restoring safetyControlled reduced tide: restoring ecology

Schelde: solutions?

Pilot studyLippenbroek

How to restore estuarine nature in an area far below MHW?

Ecology: CRT

- Introducing estuarine ecosystem

- Tidal regime in area

- Two times a day!

Ring Dike Lowered FCA dike

FCA estuary

Outlet

polder

Concept FCA – CRT safety, ecology and a new ecosystem

Safety: FCA

- Lowered dike stretch

- Critical tides: whole storage capacity

- Only few times/year!

Ring Dike Lowered FCA dike

CRT estuary

Outlet

Inlet

polder

Lippenbroek

1: Ring Dike

2: FCA dike

3: Inlet sluice

4: Outlet sluice1

23

1

4

1

1

Management scenario Lippenbroek

10 ha of tidal nature developping since March 2006

Pilot project Lippenbroek

Pilot project Lippenbroek

10 ha of tidal nature developping: May 2008

0

1

2

3

4

5

6

7

7/04 12/04 17/04 22/04 27/04 2/05 7/05

date

leve

l (m

TA

W)

Schelde (De Plaat)

Lippenbroek

0

1

2

3

4

5

6

7

7/04 12/04 17/04 22/04 27/04 2/05 7/05

date

leve

l (m

TA

W)

Lippenbroek

Schelde (De Plaat)

0

1

2

3

4

5

6

7

7/04 12/04 17/04 22/04 27/04 2/05 7/05

date

level

(m T

AW

)

Lippenbroek

Schelde (De Plaat)

Introducing macrotidal regime

Reduction of high water level by 3 meter No reduction of spring – neap variation

Introducing macrotidal regime

Intertidal habitat development

Tide - Sedimentation

-2

0

2

4

6

8

10

12

14

0 20 40 60 80 100

inundation frequency (%)

accr

etio

n r

ate

(cm

/yea

r)

Lippenbroek

"De Plaat"

Tidal marsh

Tidal flat

?

?

?

Tide - Sedimentation

Tide - Sedimentation

-2

0

2

4

6

8

10

12

14

0 20 40 60 80 100

inundation frequency (%)

accr

etio

n r

ate

(cm

/yea

r)

Lippenbroek

"De Plaat"

Low

Mean

High

Sediment(cm)

10

00

00

20

00

00

Spring 2006 Winter 20081

00

00

02

00

00

0

Spring 2006 Winter 2008

10

00

00

20

00

00

spring 2006 Winter 2008

High

Mean

Low

Aquatic species+ insects

Aquatic species + insects

Terrestric species + Insects+ others

Max densityin fine sediments200000 / m²

Zoobenthos

0

5

10

15

20

Colonising species (40)Low inundation frequency:

30 species

- Wetland + ruderal species

- Salix and Phragmites potentially dominant

Averaged inundation frequency:

27 species

- Ruderal + wetland species

- Salix, Phragmites, Typha: pot. dominant

- High inundation frequency:

10 species

- typical wetland species

- Typha potentially dominant

Phragmites australis

Ranunculus repens

Salix sp.

Lythrum salicaria

Typha latifolia Iris pseudacorus

Callitriche sp. Veronica beccabunga

Alisma plantago-aquatica

Vegetation: colonisation of bare sites

Water quality

0

25

50

75

100

125

150

175

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

time (hour)

oxy

gen

(%

sat

)

STAGNANT

STAGNANT

INFLOW OUTFLOW

Water quality: oxygen

0

2

4

6

8

10

9 10 11 12 13 14 15 16 17 18 19 20 21 22time (hrs)

DS

i (m

g/l

SiO

2)

Lippenbroek estuary

Inflow Outflow

Water quality: Silica

DSi delivery on 3/7/2006

02468

101214

16/0

5/20

06

3/07

/200

6

11/0

9/20

06

25/1

0/20

06

20/0

3/20

07

21/0

3/20

07

4/06

/200

7

5/06

/200

7

1/10

/200

7

DS

i (m

g/l

SiO

2)

-10

0

10

20

30

40

DS

I (k

g S

iO2)

Si inflow conc. Si retention

Water quality: Silica

Delivery when DSi is limiting

Water quality: Nitrogen

0

20000

40000

60000

80000

16/0

5/20

06

3/07

/200

6

11/0

9/20

06

25/1

0/20

06

20/0

3/20

07

21/0

3/20

07

4/06

/200

7

5/06

/200

7

1/10

/200

7

volu

me

(m³)

0

5

10

15

20

TDIN

(kg)

tidal volume N retention

On average 1 kg N retention per ha per tide

???

Ring dike

Overflow dike

CRT

FCA-CRT: sustainable?

Sedimentation

Flattening of the area

Changing inundation frequencies: decrease of accretion?

2.25

2.50

2.75

3.00

3.25ja

n 06

apr

06

jul 0

6

okt

06

jan

07

apr

07

jul 0

7

okt

07

jan

08

apr

08

datum

ho

og

teli

gg

ing

(m

TA

W)

S2

S4

S5

S7

S9

S10

S4

2.40

2.50

2.60

2.70

2.80ja

n 06

apr

06

jul 0

6

okt

06

jan

07

apr

07

jul 0

7

okt

07

jan

08

apr

08

jul 0

8

okt

08

jan

09

apr

09

jul 0

9

datum

ho

og

teli

gg

ing

(m

TA

W)

S4

???

future

date

Ele

vati

on

(m

TA

W)

Development of cross-section 1 (main channel)

0,5

1

1,5

2

2,5

3

3,5

0 5 10 15 20 25

Distance along cross-section (m)

Ele

vati

on

(m

TA

W)

T0

T1

T2

Erosion

Tidal marsh restoration in area below MHW is possible

Tidal regime and sedimentation can be tuned

Sedimentation rate can be reduced to preserve storage capacity

Sedimentation rate can be maximased to prepare a low site for succesful managed realignment

Lippenbroek conclusion

Tidal marsh restoration in area below MHW is possible

Tidal regime and sedimentation can be tuned

Tidal marsh restoration in area below MHW is possible

Tidal regime and sedimentation can be tuned

Sedimentation rate can be reduced to preserve storage capacity

Tidal marsh restoration in area below MHW is possible

Tidal regime and sedimentation can be tuned

Sedimentation rate can be reduced to preserve storage capacity

Ready for the big work?

Thanks

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 2 4 6 8 10 12Time (hour)

Wa

ter

lev

el

(m T

AW

)

Polder

Estuary

sluice 4.7

Start inflow

stagnant

HW Maximum inflowStop inflow Start outflow

Introducing macrotidal regime