SB07@Rivers2 Ppoint

7/31/2019 SB07@Rivers2 Ppoint

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Processes at work

From the source to mouth of a river three processes aretaking place

River Erosion

River Transport

River Deposition

RiverErosion

RiverTransport

RiverDeposition
http://www.swgfl.org.uk/riversa/eros.htmhttp://www.swgfl.org.uk/riversa/rtran.htmhttp://www.swgfl.org.uk/riversa/rdep.htmhttp://www.swgfl.org.uk/riversa/rdep.htmhttp://www.swgfl.org.uk/riversa/eros.htmhttp://www.swgfl.org.uk/riversa/eros.htmhttp://www.swgfl.org.uk/riversa/rtran.htmhttp://www.swgfl.org.uk/riversa/rtran.htmhttp://www.swgfl.org.uk/riversa/rdep.htmhttp://www.swgfl.org.uk/riversa/rdep.htmhttp://www.swgfl.org.uk/riversa/rdep.htmhttp://www.swgfl.org.uk/riversa/rdep.htmhttp://www.swgfl.org.uk/riversa/rtran.htmhttp://www.swgfl.org.uk/riversa/rtran.htmhttp://www.swgfl.org.uk/riversa/eros.htmhttp://www.swgfl.org.uk/riversa/eros.htmhttp://www.swgfl.org.uk/riversa/rdep.htmhttp://www.swgfl.org.uk/riversa/rtran.htmhttp://www.swgfl.org.uk/riversa/eros.htm


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Processes:Corrasion, (abrasion) is the grinding of rock fragments carried by the river against the bed and banksof the river. This action causes the channel to widen and deepen. This grinding is most powerful in floodtime when large fragments of rock are carried along in the river bed.

AttritionAttrition is the collision of rock fragments in the water against one another.The rock particles are broken into smaller pieces and become smoother the

longer the process continues.

River Erosion


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SolutionSolution (corrosion) is the process by which river water reacts chemicallywith soluble minerals in the rocks and dissolves them. An additional processis also at work caused by the force of the water itself known as Hydraulicaction. In this rocks are dragged away from the bed and banks by the forceof the running water. When water from a fast moving stream entersminute cracks in a rock, the pressure exerted weakens and eventuallybreaks up the rock

River Transport

A river carries or transports eroded materials such as mud, sand,boulders and dissolved materials on its journey. These materials areknown as its load. The load is carried along by three processes.

tractionsuspensionsolution

Traction

Is where boulders or stones are rolled along the stream bed by the force of thewater


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SuspensionFine particles such as clay, siltand fine sand are carried along in

the river.

SolutionDissolved materials containing minerals like calcium

and sodium are carried in the water and are invisible tothe naked eye.

River DepositionA river drops its load when the speed or volume of the river decreases. The load,which it carries, is deposited. The heavier material is deposited first andthe finermaterial carried further.Rivers reduce their speed when they enter flat land, enters a lake or the sea or

reach an arid area. The volume can be reduced during a dry season or when theriver passes over more porous landscapes e.g. sand or limestone.


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http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21393
http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21393http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21393http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21393http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21393


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What is the long river profile?
http://www.xscd.com/pub/picfolio_styles/sample_gallery/Costa_Rica/From_the_Air/Large_River_Mouth.jpghttp://www.xscd.com/pub/picfolio_styles/sample_gallery/Costa_Rica/From_the_Air/Large_River_Mouth.jpg


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River Valley DevelopmentA river has a life cycle from source to mouth. The processes at work cause changes to the river valleyand river features in the landscape that it passes over.Traditionally this cycle has been described in 3 stages, the Upper (Torrent) section, the Middle(Valley) section and the Lower (Flood Plain) section. The terminology's Youthful, Mature and Old havealso been used to describe the sections.The stages are not clearly defined but merge from one to the other and rivers show individualcharacteristics. There are river features that can be defined within a broad pattern.

A typical longprofile:

upper middle lower
http://www.swgfl.org.uk/riversa/upper.htmhttp://www.swgfl.org.uk/riversa/middle.htmhttp://www.swgfl.org.uk/riversa/lower.htmhttp://www.swgfl.org.uk/riversa/lower.htmhttp://www.swgfl.org.uk/riversa/middle.htmhttp://www.swgfl.org.uk/riversa/upper.htm


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http://www.xscd.com/pub/picfolio_styles/sample_gallery/Costa_Rica/From_the_Air/Large_River_Mouth.jpg


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Watch videos: from source to mouth


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1. How much energy do youthink the river has here? Howdo you think the river uses

its energy here?

2. How do you thinkthe channel shape

changes here?

3.In which directionis the river erodinghere? How do you

know?

4. Do you thinkthe river is at its

fastest here?What do you

think happens tovelocity as you

traveldownstream?

5. What do youthink the riversload is like here?

Why? Where

does its loadcome from?

6. What processes oferosion do you thinkmay be happening

here?

7. How do youthink the river

transports here?

8. Do you thinkdeposition occurs

here? If yes when?

9. Whatlandforms do you

find in the upperstage?


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Upper CourseCharacteristics:

Deep narrow valley

(V shaped)Interlocking spursFast flowing river(erosion predominant)Pot holes in the river

bedRapids andWaterfalls

The main process at work is the downward

or vertical erosion of the stream bed. Thiscuts into the landscape deepening the valleysides.


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As the water twists around obstacles such as rocks and boulders theerosion forces undercut outward bends and a snaking pattern isproduced. From lower down the interlocking of the spurs of landbetween the bends blocks the view up the valley.

V-shaped valley with interlocking spurs


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http://www.school-portal.co.uk/GroupDownloadFile.asp?file=55027&Groupid=12426
http://www.school-portal.co.uk/GroupDownloadFile.asp?file=55027&Groupid=12426http://www.school-portal.co.uk/GroupDownloadFile.asp?file=55027&Groupid=12426http://www.school-portal.co.uk/GroupDownloadFile.asp?file=55027&Groupid=12426http://www.school-portal.co.uk/GroupDownloadFile.asp?file=55027&Groupid=12426


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Potholes:Potholes are formed bycorrasion. Pebbles carriedby the river are swirledaround on the riverbed. Thisaction erodes the rock onthe riverbed formingpotholes. Over time, theymay widen and join with

other potholes to formlarger potholes, and thewhole riverbed is deepened.


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Rapids:Rapids are stretches of fast-flowing water tumbling over arocky-shallow riverbed. Different resistance among rockscause rapids. They are formed when the water goes from onehard rock that resists the water's erosion to a softer rockthat is easier eroded.


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Waterfalls:Waterfalls occur when a band of hard rock lies across the river with softer rock downstreamwhich is more rapidly eroded. At first rapids would form but then develop into a waterfall as th

softer rock erodes further. Variations may be caused by the rock structure.

(1) Rock layer ishorizontal

(2) Rock layer dips

upstream


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(3) Rock layer is vertical

http://www.school-portal.co.uk/GroupDownloadFile.asp?GroupId=12426&ResourceID=29560
http://www.school-portal.co.uk/GroupDownloadFile.asp?GroupId=12426&ResourceID=29560http://www.school-portal.co.uk/GroupDownloadFile.asp?GroupId=12426&ResourceID=29560http://www.school-portal.co.uk/GroupDownloadFile.asp?GroupId=12426&ResourceID=29560http://www.school-portal.co.uk/GroupDownloadFile.asp?GroupId=12426&ResourceID=29560


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Watch video: waterfall formation


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http://www.stacey.peak-media.co.uk/Year7/7-7Rivers/7-7Meanders/341.jpg


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Middle-course features

Meanders

In the middle course the river has more energy and a high volume of water. Thegradient here is gentle and lateral (sideways) erosion has widened the riverchannel. The river channel has also deepened. A larger river channel meansthere is less friction, so the water flows faster:

As the river erodes laterally, to the right side then the left side, it formslarge bends, then horseshoe-like loops called meanders.

The formation of meanders is due to both deposition and erosion.

The force of the water erodes and undercuts the river bank on theoutside of the bend where water flow has most energy.

On the inside of the bend, where the river flow is slower, material isdeposited.


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Deep, fast water and erosion on the outside of the bend

Slow, shallow water and deposition on the inside of the bend


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http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21606
http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21606http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21606http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21606http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21606


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LOWER STAGE: FLOODPLAINS


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LOWER STAGE: LEVEES

SB07@Rivers2 Ppoint

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