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Unformatted text preview: 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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This note was uploaded on 06/24/2008 for the course GEOG 1 taught by Professor Okin during the Fall '06 term at UCLA.
- Fall '06