Functions in riparian forests operate through cascades of water, sediment, nutrients, contaminants, and carbon. It is in these cascades that the lateral flow of water dominates many of the processes in riparian landscape elements, and these are the cascades that primarily link the riparian elements to the other elements in the landscape. The primary cascade of water in the riparian zone is over-bank flooding, but precipitation, groundwater flow and evapotranspiration are also important. The role of the riparian zone in the storage of water is of critical importance. Sediment and nutrient cascades are directly linked to the cascade of water. The riparian zone may be an area of net erosion or deposition, or, for some time, an area of transport where sediment inputs are balanced by outputs. The sediments moving into or out of riparian areas are often sources of nutrients for the biota and may also be sources of toxic materials. Cascades of organic energy, beginning with photosynthesis, are also important in riparian ecosystems.