Sediment (clay, silt, sand and gravel) is needed to create and maintain ocean and coastal depositional landforms and habitats, such as bars, beaches, dunes and salt marshes. Sediment transport often follows clearly defined paths (channels) but can occur over broad areas, especially during storms, when rates of sediment movement can be greatly accelerated. Transport away from a location (erosion) is often considered a negative effect, although this erosion often supplies sediment to another location (accretion) that can help maintain landforms and habitats. Flora and fauna are adapted to these changes in sediment transport, but humans are likely to view these changes as a sign of instability. Human actions can remove sediment deposits or sever pathways of sediment transport, requiring the use of mechanical equipment to artificially create or maintain depositional landforms and habitats.