These are earthen embankments, also known as levees, that are built in a river's flood plain and run parallel to the river bank along its length. The purpose of constructing these embankments is to keep river floodwaters within the cross section accessible between the embankments. If no action were taken, more than half of all land currently under water would be covered by at least one body of water during some part of the year - this is called "flooding". By building up the sides of the rivers where they enter and leave their flood plains, governments can protect people's homes and businesses from damage caused by floods. In addition to protecting against flooding, the embankments themselves can cause problems if not done properly. River banks are made of loose material such as dirt and rocks that can shift due to weather or natural forces creating gaps in the protection afforded by the bank. A common example is the loss of a house foundation due to soil erosion caused by heavy rainstorms or tornadoes. Gaps in the bank can also allow water to enter areas where it shouldn't be, causing environmental damage. For example, water entering through one side of an estate may flow across the yard until it finds an opening into another part of the property or onto public land. This can lead to problems with erosion, scouring of the soil, and changes to the natural landscape.