The past dry summers of 2018, 2019 and 2020 have indicated the sensitivity of Flemish agriculture to drought. In the Flemish polders, this resulted not only in crop water stress, but also in increasing soil and water salinity levels due to the high evaporative demand which rises the historical saline water up to the root zone. Due to the increasing occurrence of weather extremes as a consequence of climate change, farmers and farming systems will need to adapt with both too little and too much freshwater in the future. Compared to conventional drainage systems, controlled drainage can secure crop productivity and lower the irrigation need by draining water only when it is strictly necessary and thereby leaving more opportunities for water retention and groundwater recharge. As part of the project OP-PEIL, we will investigate the impact of adaptive drainage on water fluxes and availability, water quality as well as on the cropping system itself (crop growth, disease pressure, yield and quality) during 3 years. We will use geophysical techniques to monitor the impact of controlled drainage on the fresh/salt water interface in the drained field, as well as in the nearby landscape. Finally, we will set up numerical experiments using SWAP (water balance model), available historical climate, field management, and soil hydraulic properties data. This numerical experiment aims to evaluate more extensive climatological scenarios. By the end, this project will raise awareness of farmers and stakeholders about the impact of controlled drainage on agricultural practices in the Flemish Polders in Belgium.

1. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
Controlled drainage as a measure to
manage salinity in Polder context
Ali Mehmandoost Kotlar, Guillaume Blanchy, Bert Everaert, Dominique Huits,
Sarah Garré

2. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
What is Polder
• Polders are lands gained
by embarkments (dikes)
• Groundwater is saline (old
sea, WWI)
• Freshwater lens on top of
saline groundwater
• Polders are artificially
drained (ditches, tiles)
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3. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
Regular Drainage vs Controlled
Drainage
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The control pit is not
regulated, so drainage occurs
at the depth of drain pipes
(e.g. before ploughing)
The level is adjusted in the
pit, so drainage occurs at
desired depth (e.g. in
wintertime)

4. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
Salinity Dynamic in drained
fields
Stowa.nl - https://www.stowa.nl/deltafacts/zoetwatervoorziening/anti-verziltingsdrainage
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Regular Drainage
Fresh water
Saline water
Winter Summer
Regular
drainage
Controlled
drainage
Controlled Drainage

5. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
Case Study
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6. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
Observations
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• Higher GW
corresponds to
lower EC
• Intensity matters
a lot

7. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
Modelling Objectives
• How available models tackle the control
drainage scenarios?
• To what extent, water balance components are
affected by controlled drainage system?
• What is the impact of climate conditions?
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8. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
Modelling Scenarios
• SWAP-1D
• Richards Equation
𝜕𝜃
𝜕𝑡
=
𝜕𝑞
𝜕𝑧
• Drainage is a
source/Sink
• Many parameters
required
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• Implementation
of controlled
drainage

9. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
SWAP-1D
Scenario
• Whole year cultivated grass
• Layered soil profile as observed
in the field
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• Climates scenarios
Historical 1990-2020
RCP8.5 2030-2060
• Drainage Scenarios
RD: pipes located at
-90cm
CD: winter and summer levels

10. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
SWAP-1D
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Historical 1990-2020
RCP8.5 2030-2060
• Comparison of water balance components
Transpiration
Drainage
Runoff

11. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
SWAP-1D
• Transpiration increased by 5,8 cm in 2003
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Log
10
(h)

12. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
Higher Dimensional Modeling
• Hydrus 2D
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CD RD

13. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
Take home messages
• Freshwater lens increase reduces the saline
water
• There is high variability of groundwater
observations in the case studies which makes 1D
modeling questionable
• 1D models are parameter intensive while using
higher dimensional models such as Hydrus can
reduce at lease parameters related to drainage
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14. OP-PEIL | Opportuniteiten voor peilgestuurde drainage in Vlaanderen | VLAIO LA-trajecten 2021
Ali Mehmandoostkotlar
ali.mehmandoostkotlar@ilvo.vla
anderen.be
ILVO-Plant
www.peilgestuurdedrainage.be
Thank you
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www.peilgestuurdedrainage
.be