Fluvial Geomorphology

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