When is it okay to use low point drains on a mainline?

• A. When the freeze depth is 3 to 6 feet
• B. When the freeze depth is no more than 3 feet
• C. When the freeze depth is no more than 1 foot
• D. In Arid Regions only

Answer: (C)

The key idea is frost protection for irrigation mains and using a drain to purge water from the line during cold weather. Low-point drains are effective only when the soil and the buried pipe are not deeply frozen. If the freeze depth is no more than about one foot, draining the mainline at the lowest point can remove enough water so that remaining water in the line won’t freeze and cause damage.

When the freeze depth is deeper, simply opening a low-point drain may not prevent freezing inside the mainline, because the surrounding ground stays frozen deeper and water in the line can still freeze. In those cases, other winterization or protection methods are needed.

So, the best condition for using low-point drains on a mainline is when the freeze depth is no more than one foot.