Exploring the relative importance of subsurface drainage parameters, drainage control schedule, peat thickness and topography on groundwater levels in cultivated peat soils

We computationally explored how structurally different factors can control groundwater levels in peat soils. Groundwater levels emerged from the combined impact of different factors. The impact of the factors was in the same order of magnitude. The drainage parameters (median impact -0.22–0.28 m) and terrain slope scenarios (−0.10–0.18 m) affected groundwater levels more than peat thickness (−0.01–0.07 m) in simulations with regular drainage. Drainage control parameters (control depth and schedule) affected groundwater levels more (median impact 0.12–0.32 m) than the drainage parameters (drain depth and spacing, 0.05–0.25 m) in the controlled drainage scenarios. Differences in the control schedule scenarios affected groundwater levels more than the adjustments of the control depth. The impact of controlled drainage was higher in thick (range 0.05–0.45 m) than in thin (0.01–0.33 m) peat soil. The groundwater levels in the different scenarios typically deviated less from each other during the growing seasons (except for the control schedule scenarios and steep upslope conditions), which highlights the challenge of controlling the groundwater levels during growing seasons and the role of the control schedule. Controlled drainage can increase groundwater levels (median ≤0.3 m) in different conditions.