From Envirowiki

Erosion is a process of landscape change caused by wind or water movement, which wears away soil or rock. Erosion happens naturally, but anthropogenic erosion also occurs, and often such erosion is more destructive, as it happens more quickly, and ecosystems have less time to recover.

Anthropogenic erosion can come from farming (especially hard-footed animal farming), clear-felling for forestry or farming, construction (ie. dams, canals), water usage (boats can cause bank damage), and many other causes.

Erosion can be countered in a number of ways, the best of which is to leave the original ecosystems in place. If it's already past this stage, areas can be rehabilitated, and in emergency situations, solid fills such as gabion baskets can be put in place temporarily.