Assessing the movement of water through soil

Estimating the rate of subsurface drainage

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One way to approximate the rate of subsurface drainage is to bore a hole that's 1 inch to 3 inches in diameter and 4 to 5 feet deep. Such a hole can be made with a hand-operated soil auger. Lining the hole with a length of Schedule 40 PVC pipe may be a good idea, if you wish to test only the soil at the bottom of the hole. For loose-textured soils, such a liner will also help to prevent the walls of the hole from collapsing.

Fill the hole with water and return several hours later to monitor the level of water in the hole. If possible, visit the site at regular intervals over several weeks or months, each time recording with a steel measuring tape the level of water in the hole. Keep a log of rainfall and other weather-related data.

Note whether water accumulates in the hole after irrigation or heavy rainfall. If water stands in the hole more than 5 to 6 days after irrigation or heavy rainfall, then there may be a problem with drainage.

If possible, bore another hole near the first one, but 3 to 4 feet deeper. Observe whether water remains in the deeper hole after irrigation or rain. If it does, that indicates the presence of a lower layer of relatively impermeable soil.

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