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Fluvial Landforms: 

Fluvial Landforms Chapter 7

Floodplains: 

Floodplains Areas adjacent to channel inundated during floods Floodplains are built by lateral accretion on point bars and bend cut-off overbank deposition

Floodplain of meandering river may be dominated by abandoned bends: 

Floodplain of meandering river may be dominated by abandoned bends ridges on former floodplains: “accretion topography” standing water in some abandoned channels: “oxbow lakes”

Abandoned bend is now part of floodplain: 

Abandoned bend is now part of floodplain

Overbank deposition: 

Overbank deposition General over-topping of banks and deposition can result in formation of natural levees Break in levee (crevasse) can result in fan-shaped deposit on floodplain (crevasse splay deposit)

Slide6: 

Breach in channel bank results in overbank flow

Crevasse splay deposit in sandstone -- Pakistan: 

Crevasse splay deposit in sandstone -- Pakistan Photo by B. Willis

River Terraces: 

River Terraces Flat-topped, steep-sided benches elevated above floodplain Form due to relative base level fall (e.g. uplift; eustatic sea level fall) change in discharge:sediment yield

Fig. 7.12: 

Fig. 7.12 Paired terraces commonly result from rapid incision Unpaired terraces result from lateral erosion and migration

Deltas: 

Deltas Discrete shoreline protuberances formed where a river empties into ocean or lake Form from sediment deposition; delta grows if deposition rate is greater than rate at which coastal processes can redistribute sediment

Delta progradation deposits coarser nearshore sediments over finer offshore deposits.: 

Delta progradation deposits coarser nearshore sediments over finer offshore deposits.

Morphology of a Delta: 

Morphology of a Delta Delta top (subaerial channels and bays) Delta Front (subaqueous, steeply inclined) Prodelta (offshore marine, low slopes)

Influences on Delta Morphology: 

Influences on Delta Morphology River influence -- sediment load; deposition rate Wave influence -- moves sediment along shore Tidal influence -- river mouths become funnel-shaped

Nile delta -- wave dominated; Mississippi delta -- river dominated: 

Nile delta -- wave dominated; Mississippi delta -- river dominated

River-Dominated Delta: 

River-Dominated Delta Distributary channels Leeves Bays

Wave-Dominated Delta: 

Wave-Dominated Delta Wave-driven longshore drift redistributes sediment along the coast.

Tide-Dominated Delta: 

Tide-Dominated Delta Indus Delta Tidal channels and flats Tidal channels widen toward sea

Wave- & Tide-Influenced Delta: 

Wave- & Tide-Influenced Delta

Cyclic sedimentation on deltas: 

Cyclic sedimentation on deltas Deltas prograde as river brings sediment in, builds delta lobe Avulsion causes river to change course; delta lobe shifts to new location Abandoned lobe subsides

Avulsion -- major shift in river course during large flood: 

Avulsion -- major shift in river course during large flood

Deltaic Sandstone over Marine Shale: 

Deltaic Sandstone over Marine Shale

Foresets in Frewens Sandstone: 

Foresets in Frewens Sandstone