Conservation Drainage
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Providing Environmental Benefits from Artificially Drained Fields
Conservation drainage practices treat drainage water from agricultural fields that are artificially drained. These edge of field practices provide numerous environmental benefits.
Description
Conservation drainage practices help reduce the movement of sediment, nitrogen and phosphorus into surface waters from agricultural land that is artificially drained. Agricultural practices and components commonly used in Maryland include subsurface denitrifying bioreactors, saturated buffers, created wetlands, water control structures, underground outlets, and subsurface drains.
Benefits
- Conservation drainage practices remove nutrients from subsurface drainage water before it leaves the farm.
- Wetlands and saturated buffers help maintain stream flow by storing excess water and slowly releasing it into adjacent streams.
Types of Practices
- Subsurface Denitrifying Bioreactor – A buried trench filled with a carbon source, usually wood chips, and installed at the edge of a field to remove nitrate nitrogen from subsurface agricultural drainage water.
- Saturated Buffer – A biological treatment system used to divert subsurface drainage water to a vegetated area for treatment.
- Wetland Creation – A wetland is constructed at the edge of a field to treat and filter drainage water on a site that was not previously a wetland. Wetlands remove sediment, nutrients, organic matter and other pollutants from subsurface groundwater associated with farming operations.
- Water Control Structure – Used in conjunction with the above practices or as a stand-alone practice to help prevent gully erosion, manage water to improve crop production, and reduce the movement of nitrates to downstream waters.
- Subsurface Drain – An underground pipe used to collect and convey subsurface drainage water to a buffer, wetland, or bioractor.
- Underground Outlet – tubing, tile or pipe installed to move surface water from a treatment practice to a designated outlet.
Planning
- Consider how this practice may affect surface water quality.
- Will the practice impact downstream flows or aquifers?
- A subsurface denitrifying bioreactor must be designed to achieve at least a 30% annual reduction in the nitrate nitrogen load of the water flowing through the bioreactor.
- Saturated buffers must intercept a subsurface drain outlet draining at least 15 acres; buffers must be at least 30 feet wide.
- Created wetlands should be located in landscape positions and soil types capable of supporting the planned wetland functions.
- Water control structures may be used as a component of a water management system to control the stage, discharge, distribution, delivery, or direction of water flow.
- Subsurface drains and underground outlets must be installed in association with another best management practice to ensure that discharging water is subject to a nutrient reduction process.
Tech Notes
- Work with our office to determine the best conservation drainage practice for your farm.
- Cost-share funding is not available for field drainage laterals.
- Reduced cost-share funding is available for drainage mains.
Maintenance
- Trees and shrubs in the soil above and around these practices must be controlled by hand, machine, or chemicals.
- Protect outlets from rodents and other animals by installing a rodent guard.
- Conduct periodic inspections – especially following significant rainfall events – to keep inlets, trash guards, and collection of boxes and structures clean and free of materials that can reduce flow.
- Repair eroded areas to pipe outlets.