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River valley deposition: levee formation Gentle valley side River flowing above height of floodplain Flat floodplain Gentle valley side Layers of silt.

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Presentation on theme: "River valley deposition: levee formation Gentle valley side River flowing above height of floodplain Flat floodplain Gentle valley side Layers of silt."— Presentation transcript:

1 River valley deposition: levee formation Gentle valley side River flowing above height of floodplain Flat floodplain Gentle valley side Layers of silt deposited during several floods Most silt deposited right beside river channel Finest materials <<<<< Coarsest materials Coarsest materials deposited right beside river channel where water speeds are fastest, but drop soon afterwards as flooding water moves from fast channel to broad floodplain. Lighter finer materials carried further even when water speed very low

2 A classic waterfall: headward erosion (5) Wearing back off soft rock exposes hard rock overhang which eventually breaks off under its own weight (6) Water fall retreats upstream - headward erosion (7) Steep narrow gorge develops (3) Undercutting (2) Soft Rock, e.g., sandstone or shale (1) Hard Rock, e.g., gritstone or schist (4) Deep plunge pool showing downward erosion through corrasion and hydraulic action. Usually full of debris from collapses above which is getting smaller, undergoing attrition

3 Neck gets narrower Meander core Meander core Ox-bow lake Meander loop bends increasingly Fastest current on outside of bend Meander neck Slowest current on inside of bend Slip off slope River cliff River cuts through neck of land at time of flood The meander & ox-bow lake Fastest current and thalweg

4 4 Point bar (slip off slope) created on inner bank River cliff created on outer bank Lateral erosion Deposition Helicoidal flow Hydraulic action, corrasion & attrition Concave profile Convex profile Faster current (Thalweg) Slower current The meander: lateral erosion Centrifugal force Centrifugal force


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