fluvial geomorphology
TRANSCRIPT
Fluvial LandscapesFluvial Landscapes
OverviewOverviewFluvial ProcessesFluvial Processes
Basel LevelBasel LevelDownDown--cutting and meanderingcutting and meandering
Drainage Drainage WatershedsWatershedsDrainage PatternsDrainage Patterns
Stream flow and fluvial processesStream flow and fluvial processesMeandering StreamsMeandering StreamsFloodplainsFloodplainsFloodingFlooding
Base Level and Fluvial LandscapesBase Level and Fluvial LandscapesA Profound Concept: Water flows downhillA Profound Concept: Water flows downhill
Abrades and erodes the landscape as it happensAbrades and erodes the landscape as it happensAbrasion = erosion processAbrasion = erosion processCreates Creates erosionalerosional landforms landforms –– drainage patterns, cut banksdrainage patterns, cut banks
Carries eroded material downstream as either dissolved, Carries eroded material downstream as either dissolved, suspended or bed loadsuspended or bed load
Load = TransportLoad = Transport
Load becomes deposited, creating depositional landformsLoad becomes deposited, creating depositional landformsDepositional landforms: Deltas, point barsDepositional landforms: Deltas, point bars
Base Level: The lowest level that a river can erode Base Level: The lowest level that a river can erode down to.down to.
Gravity sets the water in motionGravity sets the water in motionUltimately, the water is trying to reach sea levelUltimately, the water is trying to reach sea levelLocal impediments to flow create Local impediments to flow create local base levelslocal base levels
Higher above base level, water has more potential Higher above base level, water has more potential energy, which gets converted to kinetic energy as energy, which gets converted to kinetic energy as it flows it flows downslopedownslope
Above base level, more energy directed downwards, Above base level, more energy directed downwards, more able to erode bedrock more able to erode bedrock -- downcuttingdowncuttingCloser to base level, energy directed outward with Closer to base level, energy directed outward with motion, erosion occurs more laterally motion, erosion occurs more laterally -- meanderingmeandering
Landforms associated with rivers vary by how Landforms associated with rivers vary by how high above base level the river ishigh above base level the river is
Above base levelAbove base levelSteep VSteep V--shaped valley wallsshaped valley wallsNarrow stream channelsNarrow stream channelsDistinct drainage patterns based on underlying Distinct drainage patterns based on underlying geographygeographyDowncuttingDowncutting (erosion) and transportation are the main (erosion) and transportation are the main geomorphologicalgeomorphological forces actingforces acting
Closer to base levelCloser to base levelWide stream channels (floodplains)Wide stream channels (floodplains)Valley walls characterized by terracingValley walls characterized by terracingMeandering river patterns, river deltasMeandering river patterns, river deltaslateral abrasion, transport and depositionlateral abrasion, transport and deposition
Tectonic forces can cause areas close to base level Tectonic forces can cause areas close to base level to become upliftedto become uplifted
Meandering gives way to Meandering gives way to downcuttingdowncuttingEntrenched meanders, canyonsEntrenched meanders, canyons
DrainageDrainage
When rain falls on a landscape, it drains When rain falls on a landscape, it drains from higher to lower elevationsfrom higher to lower elevations
erodes surfaces as it happenserodes surfaces as it happenslargely an largely an erosionalerosional processprocessOccurs above base level Occurs above base level -- downcuttingdowncutting
over time, forms regions of consistent over time, forms regions of consistent drainage patterns that concentrate runoff drainage patterns that concentrate runoff into specific streams and riversinto specific streams and rivers
watersheds or drainage basinswatersheds or drainage basinsdrainage patterndrainage pattern
WatershedsWatershedstopography directs flow of surface water topography directs flow of surface water into various into various downslopedownslope areasareasat high points in the topography, surface at high points in the topography, surface flow separates down different slopes, and flow separates down different slopes, and channels water into separate drainage channels water into separate drainage systemssystems
these high points are called drainage divides or these high points are called drainage divides or interfluvesinterfluvesdrainage divides form the boundaries between drainage divides form the boundaries between watershedswatersheds
Drainage PatternsDrainage Patterns
Pattern relates to Pattern relates to underlying bedrockunderlying bedrock
Type of rockType of rockSoft sedimentary layers tend to Soft sedimentary layers tend to produce produce dendriticdendritic patternspatternsIgneous or hard sedimentary Igneous or hard sedimentary bedrock tends to produce bedrock tends to produce rectangular patternsrectangular patterns
streamflowstreamflow directed through directed through orthogonal rock fracturesorthogonal rock fractures
FoldingFoldingproduces trellis patternsproduces trellis patterns
DendriticDendriticsoft underlying soft underlying sedimentary rock sedimentary rock exerts no strong exerts no strong directional influence directional influence on the flow of wateron the flow of watermost common most common stream patternstream patterna radial pattern a radial pattern occurs when soft occurs when soft layers are uplifted layers are uplifted by an igneous by an igneous intrusion (dome) or intrusion (dome) or on mountain or on mountain or volcanic peaksvolcanic peaks
TrellisTrellisOccurs where there is intense foldingOccurs where there is intense folding
antiformsantiforms and and synformssynformsalternating layers of soft and resistant rockalternating layers of soft and resistant rock
Common in AppalachiaCommon in Appalachia
RectangularRectangularOccurs on areas with Occurs on areas with resistant bedrockresistant bedrockSurface flow follows Surface flow follows rectilinear fracture rectilinear fracture pattern of the rockpattern of the rockproduces an annular produces an annular pattern when this pattern when this occurs on a domeoccurs on a dome
ParallelParallelOccur on steep Occur on steep slopesslopes
DerangedDerangedOccur where Occur where something has something has disrupted normal disrupted normal surface patterns and surface patterns and processes, such as processes, such as glaciationglaciation
Stream Flow and Fluvial ProcessesStream Flow and Fluvial ProcessesStreams run down Streams run down slopesslopes
Potential energy is Potential energy is changed to kinetic changed to kinetic energyenergy
DischargeDischargeSpeedSpeedChannel depthChannel depthChannel widthChannel width
Fluvial ProcessesFluvial ProcessesErosion: abrasionErosion: abrasionTransport: loadTransport: loadDepositionDeposition
LoadLoad
Dissolved LoadDissolved LoadSuspended LoadSuspended Load
Greatest partGreatest part
Bed LoadBed LoadTractionTractionSaltationSaltation
General Principle: The greater the speed, the General Principle: The greater the speed, the more load a stream can carrymore load a stream can carry
Slowing causes depositionSlowing causes depositionLargest and heaviest materials deposited firstLargest and heaviest materials deposited first
Meandering StreamsMeandering Streams
Erosion and Erosion and DepositionDepositionUndercut bank and Undercut bank and point barpoint bar
FloodplainFloodplain
FormationFormationWidening of valley through meandering Widening of valley through meandering processprocess
FeaturesFeaturesFloodplainFloodplainNatural leveesNatural leveesOxbow lakes and swampsOxbow lakes and swampsMeander scarsMeander scarsTerracesTerraces
Entrenched MeandersEntrenched MeandersLandscape was once near base Landscape was once near base level, and meanders formed. level, and meanders formed. Later, tectonic uplift caused the Later, tectonic uplift caused the river to be raised above base river to be raised above base level, recommencing downlevel, recommencing down-- cutting, and carving these cutting, and carving these canyonscanyons
DeltasDeltas
DepositionDepositionRiver reaches sea level (base level)River reaches sea level (base level)Velocity decreases dramaticallyVelocity decreases dramaticallyLoad is depositedLoad is depositedDistributariesDistributaries
FloodingFloodingRating (10Rating (10--year flood, 100year flood, 100--year flood, etc)year flood, etc)
an expression of probability (10%, 1%, resp.)an expression of probability (10%, 1%, resp.)
Contributing factorsContributing factorsRainfall, of courseRainfall, of course
Oscillations, hurricanesOscillations, hurricanes
Human activities that increase runoff and reduce Human activities that increase runoff and reduce soil moisture storage capacitysoil moisture storage capacity
urbanization (increasing paved surfaces)urbanization (increasing paved surfaces)agricultural practicesagricultural practices
Midwest Flood of 1993, North Carolina flood Midwest Flood of 1993, North Carolina flood of 1999of 1999
1000 year flood events (0.1% probability of 1000 year flood events (0.1% probability of occurring)occurring)Contributed to formations of Contributed to formations of ““Dead ZonesDead Zones””
Dead Zone Dead Zone (The Zone of Hypoxia in the Gulf of Mexico)(The Zone of Hypoxia in the Gulf of Mexico)Pamlico Sound, NCPamlico Sound, NC