Appalachia’s coal bearing region is typified by steep, mountainous terrain. Here, factors such as coal thickness, expected mine roof conditions, and the vertical distance between coal seams make underground mining impossible or potentially unsafe, and surface mining is used to remove coal from seams. The Surface Mining Control and Reclamation Act (SMCRA) requires that areas disturbed by surface mining be returned to their approximate original contour (AOC). The majority of rock and earth moved during active mining is temporarily stored and then returned to the mined area to restore the land to its AOC.
However, when the earth and rock are first loosened from their compact state, a natural swelling of the material takes place, to the point that there’s usually excess material left over after the mined area’s been restored to AOC. In mountainous terrain, the only places where the excess rock and dirt can be placed are the heads of hollows, the upper reaches of larger hollows, or in small valleys. Thus the term “valley fill.”
A highly engineered process is followed in constructing valley fills. For example, by law, valley fills must be constructed so that rain water that flows into the same stream system that it did prior to the disturbance.
The valleys used to place the excess rock and soil typically do not have permanently flowing streams. Rather, they may have ephemeral streams that flow only after rainfall or intermittent streams that flow seasonally. Regardless, the valley fill is engineered in a way that maintains the original course of the water from those ephemeral or intermittent streams.
Lastly, when valley fill construction is completed, by law all disturbed areas must be re-vegetated.
to view the detailed stages of valley fill engineering and construction.