What we can learn from 18 years subsidence monitoring? Lessons for the Wadden Sea Joop Marquenie and Jaap de Vlas 1
History of monitoring on Ameland 1962 Discovery gas field: 50-60 billion cubic meter 1972 Permit application 1983 Permits granted 1985 Prognoses subsidence, baseline study and impact assessment 1986 Start production 1987 Start monitoring 1994 1st report 2000 Report, review and adjustment of the program 2005 Report and review? 2018 End production 2
Monitoring based on subsidence prognose for 2020 Prediction 1985: center: content: 20-34 cm diameter: 20 km 24 x 106 m3 Prediction 2003: center: content: 31-37 cm diameter: 15 km 22 x 106 m3 Winningsplan 2003 3
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
What did we monitor? 1987-2000 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
What did we change? 2000-2005 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
Overview of monitoring stations 7
2003 assessed subsidence (27 cm) Data NAM 8
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
Photo Jaap de Vlas 10
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
Natural development of channels around De Hon 1987 1997 1994 2003 Dieptegegevens RWS/RIKZ Data RWS WL Delft Hydraulics 12
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, 1949 1996 1979 Further to the east, the marsh is growing P. Slim Alterra 13
Extension of the marsh vegetation, subsidence 20 cm 1989 K. Dijkema Alterra 1999 14
Subsidence and sedimentation De Hon PQ 9.04 (WADZIJDE) Edge Wadden Sea 250 200 1999 1998 1997 1996-50 1995 1000 1994 0 1993 1050 1992 50 1991 1100 1990 100 1989 1150 1988 150 1987 1200 opslibbing in mm 1250 1986 hoogte in mm 1300 PQ 9.08 (DUINZIJDE) 1999 1998 opslibbing in mm 0 1997 1150 1996 50 1995 1200 1994 100 1993 1250 1992 150 1991 1300 1990 200 1989 1350 1988 250 1987 K. Dijkema Alterra 1400 1986 hoogte in mm Central and dune 15
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
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 30 10 5 1 2 1 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 0 0 - S 1 3 0 ). 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. 0 0 5 5 S -1 0 0 S -6 0 10 15 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 1.5 1.0 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
Simple and accurate M. Kersten, Natuurcentrum 16 Stations (duplicate) Each station 4 anchors at 0.5 m 18
Tidal flats: 1989-2000 -1,2-2,1 4,2-2,9 7,2 9,7 9,8 Data RWS Average annual sedimentation in mm/yr 19
Pinkegat NW van -4 cm Hypsometric graph 85-90 97-02 1,50 - 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
Mean High Water variations GHW Nes 1980-2004 1200 mm t.o.v. NAP 1150 1100 1050 1000 950 900 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 GHW in mm Lop. gem. 3 jr. Poly. (GHW in mm) K. Dijkema, Alterra 21
The 18-year cycle tijverschil (cm) Tijverschil Nes 250 245 240 235 230 225 220 215 210 205 200 1960 y = 0.14x - 49.85 1965 1970 1975 1980 1985 1990 1995 2000 2005 tijd (jaar) 22
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
Sea buckthorn mortality after flooding Ameland-Oost 1994 The area did not significantly increase D. Schouten, UU 24
Flooding frequency was calculated to increase significantly - more flooding events - more sedimentation Ameland scenario 1 (2002) SPRINGTIJ 1.19 m 609000.00 F B1 E 608500.00 A C G1 DD G2 NAM B2 1.19 m SPRINGTIJ 608000.00 overvloedingsrichting 607500.00 188500.00 va lle i f (1987) z ss scenario 25 cm 189500.00 f (2002) f (2007) zss190500.00 sce na rio 50 cm 191500.00 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 3,7 192500.00 f (2007)kans op overschrijding per jaar f (2002) 600 D. Schouten, UU 4 13 20 15 B 3 9 14 11 C 2 3 5 4 D 0,5 1 2 1 E 0,3 1 1 1 F 0,2 0,5 1 0,5 G 0,02 0,03 0,05 0,04 500 HW in cm boven NAP A 400 25 17 6 300 200 100 2 2 1987 (reeks1941-1980) 1 2002 0,06 0 1000 100 2007 10 1 0,1 0,01 0,001 0,0001 0,00001 0,000001 25
10 9 8 7 5 2 1 0 28/4 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 25/03/2004 11/03/2004 26/02/2004 12/02/2004 29/01/2004 15/01/2004 01/01/2004 18/12/2003 04/12/2003 20/11/2003 06/11/2003 23/10/2003 09/10/2003 26 datum waterstand +NAP J. Krol, Natuurcentrum ground level 3 ground level 200 195 190 185 180 175 170 165 160 155 150 145 140 4 NC-15 2003-2004 = flooding event 6 NC valleinummer Inundation increased from days to months =1986-1987 =2003-2004 15 14 13 12 11
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
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
What to monitor in relation to sea level rise? 29
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
Wash-over east of locationon Ameland-Oost 32
Subsidence prognoses hampered by salt Salt rock (Zechstein) is a complexing factor in the prediction of subsidence behaviour 33
Gemiddelde jaarlijkse sedimentatie in mm/j tussen 1989 en 2000. -2,1 9,8 11,4-1,4 2,3 Elias et al: 2,4 mm 1,8 mm/j = natuurlijke zeespiegelrijzing 34