The impact of automated drainage water management on groundwater, soil moisture, and tile outlet discharge following storm events

Tile outlet discharge, soil moisture, and groundwater response were monitored for one year from a 10-ha catchment in north-central Ohio to understand the impact of automated drainage water management (ADWM) following 16 storm events. Under ADWM the tile outlet valve was programmed to open and release water when the water level in the control structure reached a user defined set point below the soil surface. Average groundwater level, soil moisture, and percentage of surface flooding indicated by groundwater levels were not significantly different following precipitation events during periods of ADWM compared to free drainage. However, the time to achieve maximum soil water moisture following precipitation onset was significantly longer and lateral hydraulic gradients were greater during periods of free drainage compared to periods of ADWM, which potentially alters how agricultural fields contribute water through edge-of-field buffers and waterways. In addition, maximum discharge occurred significantly later for storm events that occurred during ADWM; however, total tile outlet discharge was surprisingly not significantly different for events that happened under ADWM compared to events that occurred during free drainage. Tile outlet discharge for precipitation events occurring under ADWM was significantly correlated with the percentage of time during the event in which the tile outlet valve was opened. ADWM for this study was thus more effective at retaining water in the field and reducing tile outlet to near zero discharge during low-intensity precipitation events and when dry antecedent conditions were present. Our results highlight that fields under ADWM are not isolated from the surrounding landscape as they still allow water to move beyond the boundary of the field through combinations of (1) redistributions or reconnections of subsurface flow pathways and (2) periodic opening of outlet valves to release tile drainage water during large storm events and wet conditions.