What is Controlled Drainage?

What is it?

Controlled drainage is a method of water management that involves use of control structures within a traditional, uncontrolled water management system. This enables water managers to exert some level of control over the rate at which water drains from their fields, thereby allowing them to retain water during periods of drought and help mitigate nutrient loss.

Controlled vs. Uncontrolled

In short, controlled drainage is more exacting. It limits leaching and, in the process, regulates nutrient levels in and around root structures, providing a leg up on crop growth maximization.

In an uncontrolled system, when it rains, water is absorbed into the soil and then, upon reaching a level of saturation, makes its way to corrugated pipe buried beneath the surface of a field. From there the water travels, uninhibited, through a sometimes-complicated piping system to an outlet, which could be a drainage ditch, a stream, or a larger water management system altogether. As rain travels through the soil to the drainage system, it picks up nitrates and phosphorus originally applied to the ground as fertilizer. These nutrients are then carried from the soil surrounding crop root structures (where they do the most good) through piping to an outlet. Uncontrolled systems are concerning, as a result, because they potentially lead to nutrient loss, and they potentially carry nutrients and other chemicals to natural water systems.

Benefits of Controlled Drainage

Controlled drainage incorporates water control structures within an uncontrolled system. These structures function as gates within the system that allow for greater control over the rate at which water exits the management system. This provides farmers with leverage by enabling them to mitigate nutrient loss and allowing them to retain water during periods of forecasted drought.

Cost

Upfront design costs for controlled drainage are greater for obvious reasons: there’s more to consider and additional technology is implemented into the system design. The project requires more thought and foresight. It also requires investment in the water control structures themselves. Additionally, for controlled drainage to be a feasible option in a field, the slope of the field must have a grade of less than 1%. If this requirement can’t be met upon project conception, a landowner might consider engaging a contractor for additional dirt work to flatten the land to a degree allowing for use of a controlled drainage system. Another added cost might be the forfeiture of space in a field and markers for each water control structure, depending on the grade of the field and subsequently, the number of water control structures required.

Key Takeaways

Drainage, whether uncontrolled or controlled is a proven investment for farmers. And while controlled drainage won’t work for every field, when it can be implemented, it has the potential to provide considerable benefits:

Increased water retention

o   When drainage is controlled, it provides for greater soil elasticity during droughts.

Increased water quality / fewer nitrates lost

o   As water is retained, so too are nutrients originally applied to the topsoil.

Increased crop yield

o   Controlled drainage gives more power to the water manager, allowing the system operator to optimize soil aeration and nutrient retention.