Most studies of soil erosion have focused on cultivated lands. From such studies, much is known about the erosional characteristics of cultivated soils and about the erosional effects of different crops and cultivation practices, especially in countries such as the United States where soil erosion research has been extensive. The research has also been beneficial because a better understanding of the processes of soil erosion has aided the development of more effective soil conservation measures. However, serious problems involving soil erosion continue to threaten such key activities as food and hydroelectric power production throughout the world. As reservoirs fill with sediment, it becomes apparent that patterns of soil erosion in entire watersheds, not just the cultivated portions, need to be examined.