Sediment that is small or light enough to be lifted by the water deposited when

Sediment that is small or light enough to be lifted

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Sediment that is small or light enough to be lifted by the water (deposited when velocity decreases) o Bed load Traction = stays in contact with bed Saltation = series of short leaps or bounces STREAM DEPOSITION As velocity falls, largest particles settle out Results in sorting of sediment in river deposits = alluvium Most transport takes place during floods; most deposition occurs as flood waters fall Stream deposits include
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o Bars Ridge of sediments (sand or gravel) Alluvial placer deposits – concentrations of heavy particles, such as gold, platinum, other metals or gemstones Ex: Barra del Puerto o Braided streams A stream heavily loaded with sediment Sediment collects as bar deposits which separate the stream into several different channels Arid/semiarid environments o Meandering streams and point bars Meandering streams – single, continuous channel with meanders Cut bank Point bar Oxbow lake o Flood plains Sediments are deposited as a river floods its banks and the water velocity slows. Natural levees Back swamp deposits Yazoo stream o Deltas Where the stream deposits at the mouth od a body water Distributaries Stream dominated delta o Long, finger- like sand bodies o Mississippi Wave-dominated deltas o Seaward margin of delta consists of islands reworked by waves o Nile Tide dominated delta o Continuously modified into tidal sand bodies that parallel the direction of tidal flow o Ganges-brahmaputra o Alluvial fans Is like a delta except it forms with temporary streams Usually deposit in arid and dry areas, when there is snow this rivers can flood. Bajada FLOODS
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Most deposition occurs when rivers flood. Floods are the most devastating of all geologic agents - exceeded only by plagues, world wars and the holocaust in loss of life. $5 BILLION annually in the US, NOT including coastal flooding due to hurricanes. River floods can occur quickly and recede after hours/days o Flash floods- can be caused by rapid, heavy rainfall, dam failures, etc. CAN FLOODS BE PREDICTED/CONTROLLED Controlling Floods o Dams o Flood walls o Levees o Floodways – built for excess water to flow through o Channelization – speed up the flow of water and thus prevent flooding o Dikes Zoning to minimize development Prohibition of rebuilding; moving town o Not a realistic option for larger towns o Martin, KY – has flooded 37 times since 1862 NORTH AMERICAS DRAINAGE DIVIDES Drainage basins o Mississippi River Drainage basin 40% of US area Tributaries Divides DRAINAGE PATTERNS The arrangement, in map view, of a river and its tributaries o Dendritic Like tree branching Gently sloping surfaces o Radial Flows outward in all directions o Rectangular Right-angle bends Controlled by geologic structures Ex. jointing o Trellis Parallel main streams Tributaries at right angles
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STREAM VALLEYS
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