The flexible use of different water table management options allows WRSIS to provide improved crop yields and potential environmental benefits. WRSIS agricultural field water tables are managed with intake pipes and hydraulic control structures. Intake pipes allow water to be added to the buried subirrigation/drainage pipe network, and in turn, the crop root zone. Hydraulic control structures contain a weir comprised of track-mounted flashboards. There are three WRSIS water table management options.

One option is uncontrolled drainage. With respect to this option, no water is supplied through the intake pipe, and all flashboards are removed from the hydraulic control structure. After a significant rainfall event, uncontrolled drainage results in the water table quickly dropping to near the level of the buried subirrigation/drainage pipe network. This option is used intermittently during the growing season to prevent crop injury due to root zone flooding. Uncontrolled drainage is used continuously, especially during portions of the fall and spring, to help site trafficability during harvest, tillage, planting, and post emergence field operations. 

Schematic illustrating uncontrolled drainage. 

A second option is controlled drainage. For this option, no water is supplied through the intake pipe, but flashboards are inserted or remain in place within the hydraulic control structure.  If there is enough rainfall, controlled drainage allows the water table to be maintained near a level coinciding with the top of the stacked flashboards. If rainfall is not sufficient, the water table drops slowly beneath the level of the top stacked flashboard. The controlled drainage option is now being tested at the Defiance County WRSIS site during winter months to promote anaerobic conditions that decrease nitrate levels in the soil through denitrification processes, thereby limiting the amount of this nutrient/pollutant being released offsite during winter and spring months. This water table management option also has the potential to reduce organic matter biodegradation, in turn promoting soil carbon sequestration.

Schematic illustrating controlled drainage.