Earth dams are a type of embankment dam built with compacted earth, normally on sites with wide valleys. They are typically constructed in a triangular fashion with a clay- or earth-based nucleus that is dense and watertight. These types of dams consist of an impermeable earth core unable to retain water. Earth dams are among some of the most common types of dams constructed throughout the world, and are the most common type in the U.S.
The force of the water exerts itself against the embankment and is transferred to the core and pushed downwards to the foundation of the dam. The materials used in the dam give it weight that makes it resistant to the force of the water from the river, valley, or reservoir.
Earth dams have many environmental and economical benefits. As earth and clay are naturally occurring materials usually found on-site, the construction of earth dams may have less environmentally damaging implications than other types of dams. As well, aggregate does not need to be crushed, screened, and transported to the site of the dam, cutting down on costs in that area.
Some of the oldest earth dams go back as far as the ninth century, notably the Fishers Pond Dam.