Lessons for the Wadden Sea

Transcription

1 What we can learn from 18 years subsidence monitoring? Lessons for the Wadden Sea Joop Marquenie and Jaap de Vlas 1

2 History of monitoring on Ameland 1962 Discovery gas field: billion cubic meter 1972 Permit application 1983 Permits granted 1985 Prognoses subsidence, baseline study and impact assessment 1986 Start production 1987 Start monitoring st report 2000 Report, review and adjustment of the program 2005 Report and review? 2018 End production 2

3 Monitoring based on subsidence prognose for 2020 Prediction 1985: center: content: cm diameter: 20 km 24 x 106 m3 Prediction 2003: center: content: cm diameter: 15 km 22 x 106 m3 Winningsplan

4 Commission Monitoring Subsidence Ameland Monitoring on request of the Provincial Association for Conservation of Nature It Fryske Gea Independent Commission Task: Independency, quality and completeness Directly involved stakeholders Period 10 years (renewed in 2000 for 10 more years) Public evaluation every 5 years 4

5 What did we monitor? Subsidence Sea level, rainfall, evaporation Island morphology Beach nourishment Tidal flats (elevation and depth chart) Groundwater Salt marshes (grazed and non-grazed) Dunes (vegetation) Birds 5

6 What did we change? Subsidence: lower frequency Tidal flats: NEW METHOD, frequent erosion and sedimentation assessments Salt marshes: increased frequency Lower dune valleys: NEW Dunes: lower frequency Birds: assessment of feeding areas 6

7 Overview of monitoring stations 7

8 2003 assessed subsidence (27 cm) Data NAM 8

9 Subsidence and sea level rise Additive impact for marshes and tidal flats In 18 years we had: 27 cm subsidence in center 3 cm sea level rise (on global average) 20 cm year to year variation in Mean High Water 30 cm subsidence + sea level rise = 1,5 m sea level rise per century In 18 years we look a century ahead 9

10 Photo Jaap de Vlas 10

11 Island morphology develops as predicted East Cape was growing, but has reached point of erosion Beach nourishment as predicted Impact of subsidence is within natural variation W. Eysink WL Delft Hydraulics 11

12 Natural development of channels around De Hon Dieptegegevens RWS/RIKZ Data RWS WL Delft Hydraulics 12

13 Aerial photo analysis of erosion: no increase attributed to subsidence Erosion of the marsh south of Oerder dune does not seem to be influenced by subsidence, Further to the east, the marsh is growing P. Slim Alterra 13

14 Extension of the marsh vegetation, subsidence 20 cm 1989 K. Dijkema Alterra

15 Subsidence and sedimentation De Hon PQ 9.04 (WADZIJDE) Edge Wadden Sea opslibbing in mm hoogte in mm 1300 PQ 9.08 (DUINZIJDE) opslibbing in mm K. Dijkema Alterra hoogte in mm Central and dune 15

16 Conclusion morphology Large scale processes behave in a predicted manner Sea side morphology Coastal nourishment Marsh edge Sedimentation and erosion of salt marshes Edge of marsh and creeks Keeps up with subsidence and sea level (2 cm/yr) More as expected Central and higher marsh As expected and lags behind (0.5 cm/yr) A short spurt in sea level rise may not pose a problem 16

17 0 1 Tidal flats 2 km NAM S80 S70 N es S120 S10 S00 S30 S50 S110 S130 S20 S100 S90 S40 S60 b o d e m d a li n g s c h o te l s e d i m e n ta ti e s e d im e n ta tio n ( c m ) 15 ( c m / ja a r ) 10 S F 5i g u u r 2. L o k a t i e v a n d e s e d i m 2e n t a t2i e - m e e t p 2u n t e n2 o p h e t w a d o n d e r O o s t - A m e l a n d ( S S ). D e c ir k e lb o o g b e g r e n s t d e b o d e m d a lin g s c h o te l r o n d d e N A M - b o o r lo k a tie S S O 2000 J A J 2001 O J A J 2002 O J A 2003 F ig u u r 6. S e d i m e n ta ti e e n e r o s i e a a n h e t w a d o p p e r v la k o p m e e t- lo c a tie S 3 0. R e s u lta te n z ij n b o d e m d a li n g 0.5 ( c m / ja a r ) 0.0 J. Krol and M. Kersten, Natuurcentrum Ameland 17

18 Simple and accurate M. Kersten, Natuurcentrum 16 Stations (duplicate) Each station 4 anchors at 0.5 m 18

19 Tidal flats: ,2-2,1 4,2-2,9 7,2 9,7 9,8 Data RWS Average annual sedimentation in mm/yr 19

20 Pinkegat NW van -4 cm Hypsometric graph ,50 - Tidal flats increased inwadplaten height with about cm Hypsometrische curve: Alle in één beeld.5de geulen - Channels zijn dieper geworden, de platen zijn ongeveer 5 cm opgehoogd. got wider 1,00 0,50 0,00 Hoogte (m) 000,0E+0 5,0E+6 10,0E+6 15,0E+6 20,0E+6 25,0E+6 30,0E+6 35,0E+6 40,0E+6 45,0E+6-0,50-1,00-1,50-2,00 2 Surface Km Natte oppervlakte (m2) 20

21 Mean High Water variations GHW Nes mm t.o.v. NAP GHW in mm Lop. gem. 3 jr. Poly. (GHW in mm) K. Dijkema, Alterra 21

22 The 18-year cycle tijverschil (cm) Tijverschil Nes y = 0.14x tijd (jaar) 22

23 Conclusions tidal flats Subsidence is locally compensated at rates up to at least 1.3 cm per year The mechanism seems a rapid exchange between flats and channels The variation in Mean High Water levels may play a dominant role Longer and more time-series of the erosion and sedimentation measurements are needed in relation to tidal variation 23

24 Sea buckthorn mortality after flooding Ameland-Oost 1994 The area did not significantly increase D. Schouten, UU 24

25 Flooding frequency was calculated to increase significantly - more flooding events - more sedimentation Ameland scenario 1 (2002) SPRINGTIJ 1.19 m F B1 E A C G1 DD G2 NAM B m SPRINGTIJ overvloedingsrichting va lle i f (1987) z ss scenario 25 cm f (2002) f (2007) zss sce na rio 50 cm h (m+nap) 1,8 1,9 2 2,2 2,3 2,5 2,6 2,7 2,8 2,9 3 3,5 3,6 3, f (2007)kans op overschrijding per jaar f (2002) 600 D. Schouten, UU B C D 0, E 0, F 0,2 0,5 1 0,5 G 0,02 0,03 0,05 0, HW in cm boven NAP A (reeks ) , ,1 0,01 0,001 0,0001 0, ,

26 /4 21/4 14/4 7/4 31/3 24/3 17/3 10/3 3/3 25/2 18/2 11/2 4/2 28/1 21/1 14/1 7/1 31/12 24/12 17/12 10/12 3/12 26/11 19/11 12/11 5/11 29/10 22/10 15/10 8/10 1/10 25/03/ /03/ /02/ /02/ /01/ /01/ /01/ /12/ /12/ /11/ /11/ /10/ /10/ datum waterstand +NAP J. Krol, Natuurcentrum ground level 3 ground level NC = flooding event 6 NC valleinummer Inundation increased from days to months = =

27 Conclusion lower dune valleys Not in original program, lessons from doing and observing Relative groundwater table is main driving force for change Flooding frequency adds to it to a lesser extend No significant change in surface area Vegetation is expected to change Monitoring will continue 27

28 Dunes and birds Dunes (see contribution Han van Dobben) Natural succession Eutrophication Birds Increase of species that associate with sandy flats Decrease of species that prefer silt conditions and mussel beds Changes are not related to subsidence 28

29 What to monitor in relation to sea level rise? 29

30 Conclusions after 18 years: learning from doing The erosion sedimentation measurements on the tidal flats, gave interesting clues for underlying processes. Longer time-series are needed. The whole ecosystem seems extremely resilient to subsidence and therefore sea level rise Changes can be expected to be measurable in the lower dune valleys These valleys are not part of any structural program at this time, related to sea level rise and should be considered as candidates 30

31 31

32 Wash-over east of locationon Ameland-Oost 32

33 Subsidence prognoses hampered by salt Salt rock (Zechstein) is a complexing factor in the prediction of subsidence behaviour 33

34 Gemiddelde jaarlijkse sedimentatie in mm/j tussen 1989 en ,1 9,8 11,4-1,4 2,3 Elias et al: 2,4 mm 1,8 mm/j = natuurlijke zeespiegelrijzing 34