Percolation is known as the movement of water throughout soil. Measuring the percolation rate is helpful when determining if the soil drains as fast as is wanted whether from direct water with a downspout or with retention grading. The percolation rate also helps to decide how suitable this soil is for certain trees that may be planted on the property. Some need well-drained soil while others require a water-logged site.
To measure the percolation rate, dig a hole that is as deep and wide as the head of a shovel. Fill the hole with water. Watch how long it takes for the water to disappear into the hole. If the water drains quickly or less than 5 minutes, you have fast-draining soil, which is good for retention grading. If the water drains in less than an hour, the soil is draining about ½ inch an hour or 1 inch per hole, which is fine. If the water isn’t draining much at all, a swale or detention basin may be required where the soil is replaced with 2 feet of gravel at the bottom and 6 inches of soil on top. This helps water to sink instead of pooling, which will help prevent flooding during rainy season.