Transfer times in the Rhine Delta (1900-2008): Lobith discharge & Wadden Sea salinity

Impact of Dutch water management and climate variability on water transfer times through the Rhine Delta: linking Lobith discharge with Wadden Sea salinity from 1900 to 2008

Marijn van der Velde [email protected]

IIASA – International Institute for Advanced Systems Analysis

… with acknowledgements to Hendrik van Aken from NIOZ

Contents

• BACKGROUND

• APPROACH & DATA SOURCES

• RESULTS

• IMPLICATIONS BROUGHT FROM CLIMATE CHANGE

• CONCLUSIONS & PERSPECTIVES Dutch Water Management

• Large-scale coastal infrastructures for protection against the sea including the closure-dike completed in 1932 resulting in the IJsselmeer

• Mitigating river inundations and river navigability has been an important aim since the beginning of the 18 th Century

• Recently, Dutch river management is focusing on giving more space to natural river systems for environmental and flooding-prevention reasons

• Resulted in a significantly altered Dutch waterscape with an an impact on the transfer and retention times of water through the Lower Rhine Delta.

Approach

WADDEN SEA AT MARSDIEP (monthly, 1860 and onwards)

CLOSURE DIKE COMPLETED 1932

RHINE AT LOBITH (daily, 1900 and onwards) Motivation Wadden Sea environment important ecosystem with specific species & biodiversity

Subject to variable pressures including changing freshwater fluxes from land and projected sea level rise as well as anthropogenic impacts and water management interventions (e.g. closure dike)

Restoration of the fresh-salt water transition zone (closure dike brought fresh-salt water interface within the Wadden Sea)

Understanding interactions and controlling factors of the lower Rhine Delta – a complex system with many processes and actors - using a simple model

Data

Annual and interannual variability

Monthly

Daily

Figure. Time series of Marsdiep salinity and Rhine discharge measured in Lobith (all monthly values). Methods Advantages of a simple ‘model’: • Representation of a complex system with many actors and interactions • Processes with large-scale temporal variation • Easy interpretation

Link variability with transfer function:

Objective function to get transfer time and σ :

Source: van der Velde et al. GRL 2006

Three management periods

Consider three ‘management’ periods:

1. 1900-1932 (when the closure-dike was completed) 2. 1933-1971 (with a ‘natural’ discharge rate of IJssel) 3. 1972-2008 (when IJssel discharge increased from 12 to 17% of Rhine flow rate due to the operation of three lock weirs in the Nederrijn in 1971; van Aken, 2008)

In the latter period the Wadden Sea received about 100 m3s-1 more Rhine water via the river IJssel than in the earlier period, an increase of about 40%.

Source: van Aken JoSR 2008 Three management periods

Decreasing salinity

Impact management?

Increasing salinity variability

Source: van Aken JoSR 2008

IJssel discharge

1932-1971 (with a ‘natural’ discharge rate)

1972-2008 (when IJssel discharge increased from 12 to 17% of Rhine flow rate

In the latter period the Wadden Sea received about 100 m3s-1 more Rhine water via the river IJssel than in the earlier period, an increase of about 40%.

Source: van Aken JoSR 2008 Results • Good agreement • ~5 year oscillation

(R 2 = 0.76)

Figure . Monthly measured variation in salinity in Marsdiep, and one-year running mean, and one-year running mean of modeled salinity using a transfer function approach with daily discharge measured at Lobith as input from 1901 to 2005.

Results

Figure . Time series of normalized measured daily discharge and normalized modelled daily reciprocal of salinity in the Marsdiep from 1901 to 2005 with a time-lag of 1.5 month. Results: 3 periods

1901-1931 1932-1971 1972-2005

Results: transfer functions 3 periods

Travel Time St. Dev. (month) (month) 1901-2005 1.70 0.52 1901-1931 1.72 0.94 1932-1971 1.57 0.30 1972-2005 1.58 0.29 Changing seasonal behavior? Freshwater discharge Evaporation dominates dominates 0,8

0,6

0,4 Current situation after 1972

0,2 • Changing outlet scheme from lake IJssel? • Earlier spring melt? 0,0 0 1 2 3 4 5 6 7 8 9101112 0,8 -0,2 0,6 1932-1971 1870-1931 0,4 change in monthly salinity (psu) salinity monthlyin change -0,4 0,2 0,0 -0,6 -0,2 0 1 2 3 4 5 6 7 8 9101112 1972-2008 -0,4 -0,8 -0,6 -0,8

change in monthly salinity (psu) salinity monthlyin change -1,0 -1,2

Difference data-model: possible impacts?

1. Increased industrial activity after wars? 2. Salt mines? Land reclamation 3. After 1919 (Treaty of Versailles) and 1945 upstream policy changes France/Germany. 4. In 1940-45 increased of discharge to improve navigation from Germany (should be captured by model)? Deliberate flooding in the Netherlands? Implications brought from climate change • Increase in winter discharge (more winter precipitation) • Increase in spring discharge peak (lower snow buffer in Alps) • Decrease in summer discharge (less summer precipitation)

Hurkmans et al. (2010)

Conclusions & Perspectives • Good agreement salinity data and simple model • Changing seasonal salt-fresh dynamics • Impact closure dike on transport times (?) • Monthly analysis incomplete

• Only monthly salinity data: where are the original daily data? Improve resolution! Suggestions? • Derive seasonal transfer functions! • Include salinity measured at Lobith to deduce impact of Rhine salt load on Wadden Sea (difficult to distinguish from the Wadden Sea getting fresher) • Include additional monitoring points from the Rhine, IJssel lake, and the Wadden Sea Questions & References

van Aken, H.M., 2008. Variability of the salinity in the western Wadden Sea on tidal to centennial time scales. Journal of Sea Research 59, 121–132, doi:10.1016/j.seares.2007.11.001. van der Velde, M., Javaux, M., Vanclooster, M. and Clothier, B.E., 2006. El Niño-Southern Oscillation determines the salinity of the freshwater lens under a coral atoll in the Pacific Ocean. Geophysical Research Letters, 33, L21403, doi:10.1029/2006GL027748.

Please contact me: Marijn van der Velde [email protected]