Groundwater dynamics and effect of tile drainage on water flow across the redox interface in a Danish Weichsel till area

•We investigate groundwater dynamics and the effect of tile drains on flow.•We use high-frequency data and a 3D model with detailed representation of drains.•Rapid increase in head and drain discharge is seen when autumn water surplus starts.•The model was able to capture the dynamics in head and dr...

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Bibliographic Details
Published in:Advances in water resources 2019-01, Vol.123, p.23-39
Main Authors: Hansen, A.L., Jakobsen, R., Refsgaard, J.C., Højberg, A.L., Iversen, B.V., Kjaergaard, C.
Format: Article
Language:English
Subjects:
Agricultural land
Agricultural production
Catchment area
Crop production
Drainage
Drains
Dynamics
Field scale
Fluxes
Geology
Groundwater
Groundwater discharge
Groundwater flow
Groundwater table
High-frequency data
Hydrologic models
Hydrological modeling
Hydrology
Mineral nutrients
Model testing
Modelling
Monitoring
Nitrate reduction
Nitrates
Nutrient requirements
Nutrient transport
Oxidoreductions
Receiving waters
Reduction
Shallow groundwater
Slopes
Soil
Surface water
Temporal dynamics
Three dimensional models
Tile drainage
Tile drains
Water discharge
Water flow
Water table
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Summary:•We investigate groundwater dynamics and the effect of tile drains on flow.•We use high-frequency data and a 3D model with detailed representation of drains.•Rapid increase in head and drain discharge is seen when autumn water surplus starts.•The model was able to capture the dynamics in head and drain discharge.•Tile drains significantly decrease the water fluxes across the redox interface. Many agricultural soils are tile drained in order to lower water tables and improve crop production, but tile drains have a large impact on water flows and nutrient transport. The objectives of the study were to assess modelling requirements for describing shallow groundwater and tile drainage dynamics and to evaluate how tile drains affect groundwater flow across the redox interface, where nitrate reduction in the subsurface occurs. The study was conducted on a 33-hectare tile drained field within a Weichsel till area in Fensholt catchment, Denmark. The study consisted of 2.5 years high-frequency monitoring and numerical modelling using a variably-saturated 3D hydrological model (FEFLOW) with a detailed representation of the tile drain network. Field data showed extremely rapid increases, up to 1 m per day, in the groundwater heads when the autumn water surplus starts. Drain discharge was found to follow the dynamics in heads. High-frequency monitoring (at least once per day) is therefore necessary in order to capture the dynamics in shallow groundwater and tile discharge. The dynamics showed simultaneous rapid increase in groundwater heads down to a depth of 22 m, illustrating the key importance of deeper geology in understanding the hydrological processes in this area. The temporal dynamics in head and drain discharge were successfully captured by the hydrological model and the steepness of the retention curve was found to be important for this. The calibrated model was successfully tested against discharge in the stream draining a larger area. The model results showed, that tile drains affect the water flow in the area and significantly decrease the downward fluxes across the redox interface, located on average at 3.6 m depth. Tile drains therefore have a large effect on the amount of nitrate reduction in the subsurface and on the nitrate fluxes to receiving surface waters. [Display omitted]
ISSN:0309-1708
1872-9657
DOI:10.1016/j.advwatres.2018.10.022