Rivers and StreamsHydrologic CycleStreamsDrainage Basins and DividesColorado RiverDrainageBasinColorado Drainage BasinsFloodsAnnual FloodsFlash Flood, Boulder, 1894GradientGradient Decreases downstreamStream VelocityDischargeDischargeLoadLoadDeposition and ErosionDeposition, Erosion, and Valley ProfilesPotholes (Blyde River)V-shaped Valley (S Boulder Creek)No Flood PlainBarsPoint Bars, Cut Banks, Meanders, and OxbowsAntecedent StreamAnticline, Split MountainVictoria Falls (Zambesi)Mississippi DeltaStream TermsChapter 14Rivers and StreamsHydrologic CycleStreams•A stream is a body of water that is confined in a channel and moves downhill under the influence of gravity. •This definition includes all sizes of running water from a tiny trickle to the Amazon. •The total area drained by a given stream is its drainage basin.Drainage Basins and Divides•The line separating one drainage basin from another is a drainage divide. •The Continental Divide separates drainage basins of rivers that flow to the Atlantic and Gulf of Mexico from those flowing to the Pacific and Gulf of Cortez (Gulf of California).Colorado RiverDrainageBasinColorado Drainage BasinsFloods•Flash floods can occur in a matter of hours as a result of a single storm.•Flash floods are most likely in areas of high gradients.•Annual floods result from snowmelt or annual rain patterns (monsoons).Annual FloodsFlash Flood, Boulder, 1894Gradient•Gradient is the drop per mile (km).•Boulder Creek drops from 8000ft at Nederland to 5600’ in Boulder and has a gradient of 160 ft/mi (~30 m/km).•The Colorado River through Grand Canyon has a gradient of about 10 ft/mi (~2 m/km)•The lower Mississippi has a gradient of less than 0.5 ft/mi (~0.1 m/km).•Gradients usually decrease downstream.Gradient Decreases downstreamStream Velocity•Velocity is controlled by both gradient and channel size.•Steep gradients cause high velocities•Constricted channels cause high velocities.Discharge•Discharge is the total flow in ft3/s (cfs) or m3/s.•1 m3/s = ~35 ft3/s (cfs). •In a section of stream with no tributaries, the discharge is constant while the velocity and channel size may vary along the bed.Discharge•Boulder Creek is typically 10-25 cfs, but may be 500 cfs or greater in May and June.•The Colorado at Grand Junction is typically 2000 cfs, but may exceed 30,000 in May and June.•The lower Mississippi is typically 250,000 cfs but exceeded 3 million cfs in 1993 flood.Load•The load is the amount of material transported by a stream.–Dissolved load is the material in solution.–Suspended load is the material in suspension.–Bed load is the material on the bed•Saltation load is the material bouncing along the bottom.•Traction load is the material dragged along the bottom.LoadDeposition and Erosion•The amount of bed load and suspended load vary with velocity.–Where a stream widens and slows, it deposits material.–Where a stream narrows and quickens, it erodes material.Deposition, Erosion, and Valley Profiles•Actively eroding streams valleys have a charac-teristic V-shape (no flood plain).•Actively depositing stream valleys have flat bottoms (flood plain).Potholes (BlydeRiver)V-shaped Valley (S Boulder Creek)No Flood PlainFlood Plain(Yampa)Bars•Bars are material deposited by streams.–A point bar is a bar on the side of a stream.–A channel bar is a bar in the middle of a stream–A braided stream has many channels bars.•The presence of bars indicates that the steam is depositing.Point Bars, Cut Banks, Meanders, and OxbowsFlood Plain (Yampa)Flood Plain(Yampa)Braided StreamAntecedent StreamAnticline, Split MountainVictoria Falls (Zambesi)Mississippi DeltaStream Terms•Stream•Hydrologic Cycle•Drainage divide•Drainage basin•Gradient•Discharge•Load–Suspended–Dissolved–Bed•Saltation•Traction•Flash flood•Annual flood•Point bar•Channel bar•Cut bank•Meander•Oxbow•Braided stream•Antecedent
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