Berms are frequently built using some form of fill, such as sand, plant waste, rubble, or asphalt and dirt. Simply utilize the fill material for the majority of the mound, shaping it with dirt and firmly tamping it down. Outline the form of the mound and dig out any grass. Then, fill the hole with water and watch how quickly your berm disappears! The best way to keep a berm from washing away is to avoid creating an unstable area next to or on top of a wetland. If you must have an unstable area, then add more than one layer of fill so that if one layer is washed away, there will be another below it. The key to keeping a berm intact is to make sure that you put down at least two layers of fill. The first layer should be compacted very hard, especially along the base of the berm where soil tends to wash away first. The second layer should be slightly less dense than the first, allowing it to hold its shape better in case it gets washed away too. Compacted soil is important because it forms a solid foundation that can't be washed away by high tides or storms. It also filters water, providing oxygen for other plants and animals who live in or near wetlands. The more compact your fill layer is, the longer it will last.