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
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
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
You've reached the end of your free preview.
Want to read all 15 pages?