A check dam is a small dam that can be built from a wide variety of materials, including logs, rocks, and sandbags, and can be used for various purposes, for example to provide an area for sediment, silt, or pollutants, such as garbage and heavy metals, to settle and be removed from the water. This type of dam can also be used to slow water flow and retain water for purposes such as irrigation, fish farming, or livestock. Check dams are often built across drainage ditches, small streams, or in marshy, low areas called swales. The recommended specifications for a check dam are that it should be no higher than 2 feet (60 cm), that the center of the dam should be at least 6 inches (15 cm) lower than the edges, and that it should be used to drain areas 10 acres (0.04 km2) or smaller. Check dam construction is often easy and inexpensive, making them practical in poor areas with few financial and technological resources.
In developing countries, check dams are often used to increase agricultural production, replenish groundwater, and prevent soil erosion in heavy rainfall, such as monsoons. Check dams can also be used in artificial drainage ditches called bioswales that are often specifically built to remove pollutants from the water. Check dam design varies depending on the material used for construction, but the material needs to stretch across the entire channel being dammed, and often some of the material must be embedded in the soil to make sure the dam stays in place even during heavy water flow.
Three common types of check dams are stone check dams, rock check dams and log check dams. A rock check dam is usually built with 8-12 inch (20-30 cm) rocks, while stone check dams are constructed from smaller stones, commonly 2-3 inches (5-7.5 cm) in diameter. A log check dam is built by using logs 4-6 inches (6-15 cm) in diameter, and the logs must be buried in the soil to a depth of at least 18 inches (45 cm). Sandbags are sometimes used to build temporary check dams, for example in cases of flooding or very heavy rainfall.
A check dam requires frequent inspection, especially before and after heavy rainfall. The dam itself must be inspected for damage and wear, and the level of sediment behind the dam must also be measured. Such sediment can interfere with the function of the dam, and it must sometimes be removed or the dam can fail.