Geologic Action of river.pdf

Rivers are powerful geological agents that shape the Earth's surface through a variety of processes. The geologic action of rivers includes erosion, transportation, and deposition, which collectively contribute to the formation and modification of landscapes. Here's a brief overview of these processes:

Erosion:

Abrasion: The river carries sediments (such as rocks and pebbles) that can wear away the riverbed and banks over time.
Hydraulic action: The force of flowing water can dislodge and transport loose particles, further eroding the riverbed.
Transportation:

Traction: Large particles, like boulders and pebbles, are rolled along the riverbed by the force of the water.
Saltation: Smaller particles are bounced or skipped along the riverbed.
Suspension: Fine particles, like silt and clay, are carried in the flow of the water without directly touching the riverbed.
Solution: Dissolved minerals are carried in the water without being visible, contributing to the river's overall load.
Deposition:

When the velocity of the river decreases, it loses the ability to transport certain sizes of particles. As a result, these particles are deposited along the riverbed or banks.
Larger particles are deposited first, closer to the river source, while smaller particles may be transported farther downstream before deposition.
Meandering and Oxbow Lakes:

Over time, rivers can create meanders or bends in their course. As the outer bank of a meander erodes and the inner bank accumulates sediment, the meander may migrate.
Eventually, a meander may become so pronounced that the river cuts through the neck of the meander, forming an oxbow lake.
Delta Formation:

When a river enters a standing body of water, like an ocean or a lake, the reduced velocity causes sediment deposition. This can lead to the formation of a delta, a fan-shaped landform composed of sediment carried by the river.
Canyon Formation:

In areas with resistant rock layers, rivers can erode deep canyons over time. The Colorado River carving out the Grand Canyon is a notable example.
Valley Formation:

Rivers contribute to the formation of valleys through erosion and transportation of sediment, shaping the landscape over millions of years.
The geologic action of rivers is dynamic and continuously shapes the Earth's surface, playing a crucial role in the ongoing process of landscape evolution

1. Engineering Geology
Geologic Action of river
Sanjivani College of Engineering, Kopargaon
Civil Engineering Department
(An Autonomous Institute Affiliated to S.P.P.U. Pune)
Presented By:
K.D.PETARE
Asst.Professor Civil Engg.Dept.
[email protected]

2. Geomorphologyisthestudyoflandformsandlandscapes,
includingthedescription,classification,origin,development,
andhistoryofplanetarysurfaces.Duringtheearlypartofthis
century,thestudyofregional-scalegeomorphologywastermed
"physiography".
Thenaturalprocesseswhichareresponsibleforthe
visiblechangesontheEarth’ssurfacearecalledgeomorphic
processes.Agentsofgeomorphicprocessesarewind,water,ice
gravity,temperature,atmosphericgases,organisms,
earthquake,tectonicforcesandvolcanoes.

4. Geologic Action of river
ARiverisabodyofwaterthatcarriesrock
particlesanddissolvedionsandflowsdownslope
alongaclearlydefinedpath,calledachannel.Thus,
streamsmayvaryinwidthfromafewmetersto
severalkilometers.Streamsareimportantforseveral
reasons.

5. •Head-Wherethestreamstarts,thetopofthestream.
•Mouth-Wherethestreamflowsintoanotherstream,alake,an
ocean.
•Channel-Theareaoccupiedbythewaterflowinginthe
stream.
•Bed-Thebottomofthechannel.
•Gradient-Theslopeofthestream.
•Upstream-Towardthehead,upthegradient.
•Downstream-Towardthemouth,downgradient.

6. Arivercanerodematerialfromits
bedandbanksin4mainways
HydraulicAction-
Theforceofrunningwatercansetparticlesinmotion.Loose
particlescanbeliftedbyturbulentflow.Thehigherwater
velocity,thelargerandgreaterquantityofparticlescanbe
lifted.
Cavitation-
Cavitiesaredevelopedontheriverbedwhereimpactof
waterathighspeedtakesplace.

7. Abrasion-
Solidparticlesinsuspensionandinthebedloadcanscourthe
channel.Bedrockcanbeerodedandchipped,sedimentparticles
aresmoothedandrounded.Potholesaresemicircularholes
scouredoutineddycurrentsbyswirlingsandandgravel.
Attrition-

8. River Transportation

9. The River’s Journey
Riversusuallybegininthemountains.
Theyflowdownhillontoflatlandandintothesea

10. Stages of River
•YouthfulStream
•Steepgradients
•V-shapedcrosssections
•Roughsedimentsflowingrapidlydownstream.
•Duetogreaterwatervelocitylargersedimentcanbe
moved.

12. Features of Youth stages
Pothole formation

14. Waterfalls
Soft rock is easy to erode, but
the hard rock is resistant.
So over time a ledge develops.
Hard Rock –Lava
Soft Rock –Sandstone or Conglomerates

15. The water rushes over the
ledge and erodes a plunge pool
by abrasion and hydraulic
action.
The ledge collapses into the
plunge pool, where the
debris helps to speed up the
erosion.

16. V –shaped valley
Form due to a combination of
the following processes:
Vertical erosion by the
river itself.
Physical weathering (eg:
frost action) which provides
debris to move down slope.
Mass movement (inc: soil
creep & landslides) to move
debris down slope.

18. Mature Stage
•Potentialenergyforcuttingandremovingrock
becomesless.
•Theaveragegradientisdecreased.
•Velocitynearthebedbecomesless.
•Thesizeofsedimentthatcanbemoveddecreases.
•Bedbecomescoveredwithloosematerial,thus
protectingitfromfurthererosion.

19. •Cutting action of the stream becomes very slow.
•The base of the V has been widened due to
weathering and the action of tributaries the valley
now has gentle slopes.
•Meanders begin to form
•There is an increase in the volume of water that is
carried.
•A greater mass of sediment can be carried, but
most of it is silt and clay.

21. Features of mature stage

23. Old Stage
•Gradientbecomesextremelysmallandonlythe
finestofsedimentscanbemoved.
•Duringtimesofpeakflowthebankswilloverflow
andfloodthenearbyportionsofitsvalley.
•Whentheflowsubsidesalayerofsiltandclayisleft
behindonthevalleysurface,thisisthefloodplain.

24. Features of old stage
Deltas
•Anestuaryiswherearivermeetsthesea(itistidal).
•Deltasareessentiallytheseawardextensionofthe
floodplainandformwheretidesaretooweakto
removedepositsediment.

27. An alluvial fan
Caused when a stream falling
from a side valley reaches flatter
ground on the valley floor.
Material is dropped at the ‘break
of slope’to form this fan shape.
alluvium = silt deposited by a river

28. Ox-bow lakes
Downstream migration of meanders produce pronounced meander loops which
may form ox-bow lakesduring flood conditions
1 Lateral erosionon outside of bends of pronounced meander
2 Narrow neck of meander gradually becomes narrower
3 Neck is cut through by river during floods and river forms new straighter channel
4 Cut-off is sealed by deposition
5 Ox-bow lake begins to silt up

29. Alluvial fans
Thealluvialmaterialwhichflowsdownfrommountains
accumulatesatfoothillswherethestreamentersaplain.
Thedepositionoccursduetoabruptchangeinthegradient
ofrivervalley.Suchdepositsspreadoutintheshapeofflat
fansandarecalledalluvialfans

31. Flood plains-
Duringfloodsariveroverflowsitsbankand
submerges.Theadjacentlow-lyingareaswhere
depositionofalluvialmaterialtakesplace.Awidebeltof
alluvialplainformedinthiswayoneithersideofa
streamisfloodplain.

32. Floodplain
River Cliff
Pebble deposits on the inner meander bend
where there is low energy