Department of Biosystems & Agricultural Engineering Drainage

Q: Should I use a 3-inch or 4-inch lateral drain pipe?

A:

• Equal rate of water removal: In terms of water entry into the pipe, both 3- and 4-inch 4-row pipes drain water at the same rate. The 4-inch lateral pipe does not drain faster than the 3-inch pipe.
• Different pipe capacity: The 3-inch pipe has a lower pipe capacity, so it fills with water and reaches its maximum capacity over a shorter length than a 4-inch pipe. Use the maximum lateral length tool to see the difference (change the pipe from 4 to 3 inches).
• Option to boost performance: A pipe with 8-rows of perforation drains faster than a 4-row pipe, but the 3-inch pipe does not come in 8 rows. The 4-inch pipe comes in 8 rows of perforation that boost drainage performance.
• Sediment and root clogging risk: The 3-inch pipe clogs sooner if there\'s sediment entry into the pipe or root clogging because the cross-section area of the pipe is smaller than a 4-inch pipe.
• Grade error: 3-inch lateral has less grade-error forgiveness. If poor installation results in grade error (an off-grade dip or hump in the pipe), it will be worse in the 3-inch pipe than the 4-inch pipe. The dip of hump can lead to water standing in the pipe, thereby increasing the chance of root clogging.
• Price: The price difference between 3- and 4-inch is small, so the installer should evaluate if the cheaper pipe is warranted.

Q: My established (over 3 years old) alfalfa field has controlled drainage structures. I would like to know how much water I can/should hold back without doing detrimental harm to the roots. What about wheat?

A: I recommend that the stoplogs not be used to manage water during winter and spring when growing alfalfa. In other words, do not hold back any water, and maintain free drainage during winter and spring. This is because alfalfa roots are very deep and holding the water table close to the ground can cause harm. The same applies to wheat.

Q: Can I use controlled drainage with clay tile? Will I get tile blowout or sinkhole?

A: If the clay tile is intact and has not collapsed, you should not have tile blowout.

Q: Should I invest in subsurface drainage on a rented farm?

A: Tile investment is done by the landowner because it increases the value of the land. In the scenario that the land operator wants to invest in the drainage system, the rental value should not increase as the operator is paying for the drainage system. In addition, the operator and landowner should agree on having a long-term lease that provides enough time to pay off the drainage-installation loan. In other words, the lease term should be greater than the amortization period of the drainage-installation loan. Otherwise, a buyout clause should be added to the lease agreement. For additional information, read this economics page.

Q: Does frost depth impact drains?

A: It\'s best to place drains below the frost depth to prevent damage and have continuous flow throughout the cold season.

Q: When water is released from a water control structure, does high-velocity flow damage the tile line? Should I remove the stoplogs gradually to prevent this damage?

A: Yes, if the soil has high sand content, and if you have a perforated pipe coming into and out of the structure. Usually, several-feet-long sections of non-perforated pipes are used downstream and upstream of the structure, and this should not be an issue with clay soils.

Q: What happens if you install new drains half-way between the existing drains?

A: By adding new drains into the old system, more water will flow into the existing main. If the existing main was designed for the existing drains and not the new drains, the main size needs to be upgraded to convey the additional water. If the main size was not designed to handle the new drain, the drainage system\'s performance will be limited to the main and outlet capacity.

Q: How does an Agri Drain Water-Gate work?

A: The Water-Gate acts as an underground structure that can backup water upstream. Ohio research has shown that the water gate can effectively create a stair-step water upstream. If Water-Gate is used in a sandy soil, sediments may prevent the gates from closing or opening. Also, fields with surface inlets should be avoided as sediments from the surface inlets can clog the Water-Gate. Agri-Drain manufacturers these in 8" and 10" sizes.

Q: What is piping around main pipes?

A: Soil getting pulled into the main from the surrounding soil is called piping. Piping occurs when the main has too much grade, and thereby causing excessive water velocity in the main.

Q: If we cut through all the old clay/plastic tile with a new system, will the old tile pose a problem with the new. For example, will there be soft or mushy spots where water might accumulate? Or will the water merely find its way to the new tile?

A: If the broken tile has enough head pressure, it will cause water to come to the surface and cause a wet spot. If the broken tile is cut enough times that there is insufficient head pressure, water will not come to the surface.

Q: How to incorporate conservation practices into land leases?

A: Communication and planning are needed for landowners and tenants to include conservation in the land lease. For additional information, see news article.

Q: What’s the difference between drainage design for heavy clay and sandy soils?

A: Heavy clay soils can be drained with shallower drain depths and closer drain spacings. Coarse-textured sandy soils can be drained with deep drain depths and wider drain spacings while needing drain sock.

Q: I recently installed new plastic drains, but after a few months, I have water ponding and the drains were not flowing as much as they should. What is the problem?

A: You may have an under-performance issue. Click here for more information.

For additional frequently asked questions about drainage, see University of Minnesota Drainage page here.