Other Controlled Drainage Management Considerations
The level of management required depends on whether the water control structures will be used to raise the system outlet during the fallow season, the growing season, or both. During the fallow season, the only management required is to raise the outlet after harvest and field operations in the fall, and to lower it about two weeks before the start of field operations in the spring. During the growing season, management may involve temporarily lowering the outlet height to increase the drainage during periods of heavy rain or sustained wet periods. Automated devices are available to aid in management. From Questions and Answers About Drainage Water Management for the Midwest (Purdue Extension).
Current recommendations are to place the control structure outlet within 6 inches of the field surface for maximum water quality benefits in the winter months. (Some surface ponding might occur in depressional areas of the field.) Researchers have yet to determine the optimum outlet height during the growing season, but they suggest an outlet depth of 2 or more feet below the field surface. The goal is to provide enough drainage for good aeration and root development but to capture some of the water that would otherwise drain out under conventional systems. From Questions and Answers About Drainage Water Management for the Midwest (Purdue Extension).
The USDA National Resource Conservation Service (NRCS) has approved conservation practice standards that support drainage water management in some states. The standards are 554, "Drainage Water Management," and 587, "Structure for Water Control." From Questions and Answers About Drainage Water Management for the Midwest (Purdue Extension).
When installing a new tile system, the layout to optimize controlled drainage will often have to be on a contour, and not straight. This may add to installation costs.
Another management option for reducing nutrient loading is the use of bioreactors.