Combined effects of erosion & depositionPresentation Transcript
Combined Effects of Erosion & Deposition• Pools and Riffles• Meanders and Ox-bow lakes• River Terraces
Pools and RifflesPools: are areas of deep water and greater erosion. (Energy build up due to less friction)Riffles : are areas of shallow water caused by deposition of coarse sediment
SinuosityIs the curving nature of a river’s course.
ThalwegThe position of the rivers fastest flowing current.(Least friction, greater energy, greatest erosion)
Thalweg – the line of fastest flow in a river
Meander – Bends in course of a river channel
How occur?1. Begin when a river approaches its middle course & gradient channel is less steep.2. It results from helicoidal flow with faster current spirals downstream in corkscrew fashion.3. Movement result in erosion on outside bend of meander to form river cliff and deposit on inside bend called slip off slope.
Slip-off slope River cliff Point barThalweg
Material is deposited on the inside of a meander bend as apoint bar. At point bars particles are usually graded in size (sorted) with the largest particles found on the upstream side.
As erosion occurs on the outside of the meander bend, thewhole meander migrates downstream. Material forming the point bar becomes a contribut ory factor in floodplain formation.
As sinuosity Temporary straightening of increases, the channelduring flood means the main events the flow is in mid flow may channel, meaning cut of the deposition now meander occurs at thebend at the river banks and neck, thus the old curve is shortening therefore its course. abandoned to leave an ox-bow lake.
River / Fluvial Terraces• Benches on the valley side• Formed when a river cuts into a former floodplain Following vertical erosion caused by rejuvenation• Can be formed in bedrock• Result from AGGRADATION f0llowed by INCISION of a river valley