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Chapter 14 Outline

Chapter 14 Outline - Chapter 14 River Systems and Landforms...

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Chapter 14: River Systems and Landforms Introduction Rivers= water supply, process (dilute/transport) waste, etc; ~1250 km 3 water flows thru Earth’s water- ways at any moment= major agent of landmass denudation; rivers w/greatest discharge (stream’s vol of flow per unit time)= Amazon, Orinoco (S America), Congo (Africa), Chang Jiang (Asia) etc Hydrology - science of water, its global circ, distribution, properties- esp water at/below earth’s surface Fluvial Processes and Landscapes Stream-related processes= fluvial ; river - trunk stream/entire river sys; stream - gnrl term, may not be size-related; insolation, gravity power hydrologic cyc, are driving forces of fluvial sys’s; indv streams vary w/climate, composition of surface, topography, nature of veg/plant cover, length of time operating Water dislodges/dissolves/removes surface material in erosion ; streams=> fluvial erosion - wthred sediment picked up for trnsprt to new locations; stream = mix of water/solids; latter carried in solution/ suspension/by mechanical transport; materials laid down by deposition Alluvium - gnrl term for clay/ silt/other unconsolidated rock/mineral frags deposited by running water as semi/sorted sediment on floodplain/delta/streambed Base Level of Streams Base level - lvl below which stream can’t erode its valley; ultimate base lvl = sea lvl, avg lvl btwn high/ low tides; but not every landscape has degraded all way to sea lvl- other intermediate ones- local base level /temp’ry one may control lower limit of local streams- eg river/lake/hard, resistant rock/dam Over time, work of streams modifies landscape grtly; landforms produced by: 1) Erosive action of flowing water & 2) Deposition of stream-transported materials Drainage Basins Every stream has drainage basin ranging in size tiny-vast; defined by ridges tht=> drainage divides - div’g lines tht control into which basin precip drains; d’ge divides define watershed - catchment (water-receiving) area of d’ge basin; in drainage basin, water initially moves downslope in thin film: Sheetflow /overland flow; high ground tht separates valleys, directs sheetflow= interfluve ; surface runoff conc’s in rills - sml-scale downhill grooves, which can=>deeper gullies=>stream course in vlley Drainage Divides and Basins Svrl high d’ge divides- continental divides - in US, CAN; =extensive mtn, highland regs tht separate d’ge basins, sending flows Pacific/Gulf of Mex/Atlantic/Hudson Bay/Arctic Ocean; the divides=> water-resource regs, provide spatial framework for water-management planning Major d’ge basin sys made fr many smlr d’ge basins; each gathers, delivers its precip/sediment lgr basin, conc’g vol into main stream; eg Mississippi-MO-Ohio River sys drains 41% of cont’l US; each contributing d’ge sys adds its discharge, pollution, sediment load to lgr river Drainage Basins as Open Systems D’ge basins=open sys’s w/inputs incl precip, minerals/rocks of reg’l geology; energy/materials redistri-
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