FLUVIAL PROCESSES AND LANDFORMSFLUVIAL PROCESSES AND LANDFORMS

Unit six

The Dynamics of Earth’s environment presentation

by: S.T GIS postgraduate program (BDU)

Email: stsolt82@gmail.com

IntroductionIntroduction Running water present in almost all Running water present in almost all

environments, at least occasionally but environments, at least occasionally but other agents are limited to small parts of other agents are limited to small parts of the continents (action of wind, waves the continents (action of wind, waves and currents) or glacial ice.and currents) or glacial ice.

Nearly every part of the Earth has seen, at Nearly every part of the Earth has seen, at sometime in it’s geologic past, the imprint sometime in it’s geologic past, the imprint of fluvial processes. of fluvial processes.

In this paper we will discussed about the In this paper we will discussed about the various types of erosion, features of various types of erosion, features of drainage basin and types of drainage drainage basin and types of drainage pattern geomorphic works of rivers: pattern geomorphic works of rivers: erosion, transportation and deposition, the erosion, transportation and deposition, the development of river valley, the stages of development of river valley, the stages of river and various land forms associated river and various land forms associated with these courses. with these courses.

Learning objectivesLearning objectives

Explain briefly the various forms of surface and Explain briefly the various forms of surface and cannel erosioncannel erosion

  Describe the features of a drainage basin. Describe the features of a drainage basin. Explain how drainage patterns within a drainage Explain how drainage patterns within a drainage

basin form. basin form.   Explain the factors that control the processes of Explain the factors that control the processes of

river erosion,river erosion, transportation, and deposition.transportation, and deposition. Describe channel patterns and explain its role in Describe channel patterns and explain its role in

stream flow. stream flow.   Describe the processes and feature formed from Describe the processes and feature formed from

fluvial processes.fluvial processes.   Compare and contrast the several types of deltas.Compare and contrast the several types of deltas.

By the end of this unit you will be able to:

WATER AS AN AGENT OF WATER AS AN AGENT OF DEGRADATIONDEGRADATION

Of the of other agents of erosion, Running Of the of other agents of erosion, Running water (moving water), aides by mass water (moving water), aides by mass wasting, is the most important geologic wasting, is the most important geologic agent in eroding transporting and depositing agent in eroding transporting and depositing sediment. sediment.

Almost every landscape on the earth shows Almost every landscape on the earth shows the result of stream erosion or deposition. the result of stream erosion or deposition.

Water erosion is a two-part process involving Water erosion is a two-part process involving the detachment and transport of weathered the detachment and transport of weathered materials. materials. 

Erosion from water typically occurs in the Erosion from water typically occurs in the following ways.  following ways.  

Surface erosion Channel erosion

1. Surface Erosion1. Surface Erosion Water moving on the surface without being Water moving on the surface without being

confined to a channel. The two forms are : confined to a channel. The two forms are : splash and sheet erosionsplash and sheet erosion. .

A. Splash ErosionA. Splash Erosion First step in the erosion process First step in the erosion process Raindrops typically fall with a velocity of Raindrops typically fall with a velocity of

20-30 feet per second. 20-30 feet per second. Disaggregating and displacement of wet Disaggregating and displacement of wet

surface soil creating small craters in bare surface soil creating small craters in bare soil.soil.

Energy of these impacts is sufficient to Energy of these impacts is sufficient to displace soil particles as high as two feet displace soil particles as high as two feet verticallyvertically

splash erosion Cont…splash erosion Cont…

B. Sheet ErosionB. Sheet Erosion Gradual removal of a uniform layer of soil Gradual removal of a uniform layer of soil

from the surfacefrom the surface Entrainment of loose particles in overland Entrainment of loose particles in overland

flowflow Overland flow on smooth slopes is laminar Overland flow on smooth slopes is laminar

(layered), so particles can only be displaced (layered), so particles can only be displaced but not suspended but not suspended

Difficult to detect its effect until it develops Difficult to detect its effect until it develops into rill erosioninto rill erosion

The potential for sheet erosion is dependent The potential for sheet erosion is dependent on the on the soil type, velocity, vegetation, gradient soil type, velocity, vegetation, gradient and volume of flow and volume of flow over the surface. over the surface.

Long slopes, steep slopes, and slopes that Long slopes, steep slopes, and slopes that carry higher volumes of runoff are more carry higher volumes of runoff are more susceptible to sheet erosionsusceptible to sheet erosion

Sheet ErosionSheet Erosion

2. Channel Erosion2. Channel Erosion

Water is confined to long trough-like Water is confined to long trough-like depressions called channeldepressions called channel

A.A. Rill ErosionRill Erosion

The first stage of channel erosion and The first stage of channel erosion and intermediate process between sheet and intermediate process between sheet and gully erosiongully erosion

Are many closely spaced, innumerable and Are many closely spaced, innumerable and small shallow channels eroded by threads of small shallow channels eroded by threads of turbulent flow turbulent flow

Rill Erosion

B. Gully ErosionB. Gully Erosion Larger versions of rillsLarger versions of rills Most gullies extend up slope as a result of headwall Most gullies extend up slope as a result of headwall

migration. migration. It is the collapse and slumping of the sidewalls, It is the collapse and slumping of the sidewalls,

which usually contributes the greatest proportion of which usually contributes the greatest proportion of soil loss.soil loss.

A

C. Stream ErosionC. Stream Erosion Eventually gullies develop into streams.Eventually gullies develop into streams. Streams/Rivers contain more water and Streams/Rivers contain more water and

have more capacity to do the work of have more capacity to do the work of erosion, transportation and deposition.     erosion, transportation and deposition.    

Stream channel erosion consists of both Stream channel erosion consists of both streambed and stream bank erosion. streambed and stream bank erosion.

In this paper the words stream and river are In this paper the words stream and river are used interchangeably. used interchangeably.

· Forms erosion on an exposed slope

River as a SystemRiver as a System Drainage/ River/ BasinsDrainage/ River/ Basins River is anybody of fresh water flowing from an River is anybody of fresh water flowing from an

upland source to a large lake or to the sea, fed by upland source to a large lake or to the sea, fed by such sources as springs and tributary streams. such sources as springs and tributary streams.

A river starts on hillsides as small channels, or rills.A river starts on hillsides as small channels, or rills. The rills combine to make larger channels or The rills combine to make larger channels or

tributaries that eventually come together, forming tributaries that eventually come together, forming distinct streams.distinct streams.

The largest channels formed by this convergence of The largest channels formed by this convergence of tributaries are rivers, and they can carry large tributaries are rivers, and they can carry large quantities of fresh water and sediment across quantities of fresh water and sediment across continents. continents.

The world’s longest riversThe world’s longest rivers

River nameRiver name ContinentContinent Total lengthTotal lengthNileNile AfricaAfrica 6695 Km6695 KmAmazonAmazon South AmericaSouth America 6400 Km6400 KmYangtzeYangtze AsiaAsia 6300 Km6300 KmMississippi-Missouri-Red RockMississippi-Missouri-Red Rock North AmericaNorth America 5970 Km5970 KmYeisey-AngaraYeisey-Angara AsiaAsia 5550 Km5550 KmYellow RiverYellow River AsiaAsia 5464 Km5464 KmOb’-IrtyshOb’-Irtysh AsiaAsia 5410 Km5410 KmRio Parana-ril grandeRio Parana-ril grande South AmericaSouth America 4500 Km4500 KmAmur-shilkaAmur-shilka AsiaAsia 4416 Km4416 KmLenaLena AsiaAsia 4400 Km4400 KmCongoCongo AfricaAfrica 4374 Km4374 KmMackenzie-Peace-FinlayMackenzie-Peace-Finlay North AmericaNorth America 4241 Km4241 KmMekongMekong AsiaAsia 4200 Km4200 KmNigerNiger AfricaAfrica 4180 Km4180 Km

Cont’dCont’d

Cont’dCont’d Rivers have different sources. Rivers have different sources. They may start from the melt waters of They may start from the melt waters of

glaciers, e.g. Rhone (France), lakes, e.g. Nile glaciers, e.g. Rhone (France), lakes, e.g. Nile (Africa), springs, e.g. Thames (England) from (Africa), springs, e.g. Thames (England) from regions of steady rainfall, e.g. Zaire (Africa).regions of steady rainfall, e.g. Zaire (Africa).

Likewise, they may end at in the sea, e.g. Likewise, they may end at in the sea, e.g. Amazon (Atlantic), the Niger (Gulf of Guinea) Amazon (Atlantic), the Niger (Gulf of Guinea) and the Indus, (Arabian Sea). Sometimes the and the Indus, (Arabian Sea). Sometimes the mouth could be in a lake, e.g. Volga mouth could be in a lake, e.g. Volga (Caspian), or in a swamp, e.g. Chari River (Caspian), or in a swamp, e.g. Chari River (Lake Chad). (Lake Chad).

Moves from its sources to its mouth captures Moves from its sources to its mouth captures several tributaries.several tributaries.

Sources of Stream Flow

Cont’d

Cont’dCont’d Geologists have devoted much time and effort to the Geologists have devoted much time and effort to the

study of drainage systems and their evolution. The study of drainage systems and their evolution. The reasons for their interests are:reasons for their interests are:

Firstly, there is the obvious point that a drainage Firstly, there is the obvious point that a drainage system is a major feature of the physical landscape.system is a major feature of the physical landscape.

Secondly, evolutionary studies of drainage systems Secondly, evolutionary studies of drainage systems may afford valuable information about the may afford valuable information about the denudational history of an area. For instance, it is denudational history of an area. For instance, it is often useful to attempt a reconstruction of the often useful to attempt a reconstruction of the initial form of a river system in order to gain initial form of a river system in order to gain evidences of the nature and mode of origin of the evidences of the nature and mode of origin of the land surface on which that system began its land surface on which that system began its existence. existence.

Cont’dCont’d A A drainage basindrainage basin is a portion of the Earth's surface is a portion of the Earth's surface

that contains a main stream and its tributaries.that contains a main stream and its tributaries. Drainage divide-Drainage divide- a ridge or strip of high ground a ridge or strip of high ground

dividing one drainage basin from another. dividing one drainage basin from another. It determines into which basin precipitation flows. It determines into which basin precipitation flows.

The upland between tributaries is called The upland between tributaries is called interfluves.interfluves.   

Mississippi river basinMississippi river basin Cont’d

North America drainage systemNorth America drainage system

Continental divide

Cont’d

Cont’dCont’d Streams within the drainage basin are Streams within the drainage basin are

either perennial or intermittent in flow. either perennial or intermittent in flow. Perennial streams -permanent streams Perennial streams -permanent streams

that flow all year.that flow all year. Intermittent stream — a stream Intermittent stream — a stream

that carries water only part of the that carries water only part of the year.year.

Tributary streams- small streams that Tributary streams- small streams that enter into the main stream. Some enter into the main stream. Some streams are classified as streams are classified as exotic exotic streamsstreams, originate in a humid region but , originate in a humid region but flow through an arid region. E.g.. Nile flow through an arid region. E.g.. Nile and Colorado Riversand Colorado Rivers

Superposed StreamsSuperposed Streams

Development ofwater gap

Folded Units

Cont’dCont’d

Stream ordering Stream ordering system system

• First order streams The smallest streams in a drainage network have no tributary streams.•Second order Two first order streams unite to form a second order stream. •Third order -only have second and first order streams as tributaries, etc. •The main stream is always the highest order in the basin

Cont’dCont’d Drainage densityDrainage density is the total length of is the total length of

streams per unit area.streams per unit area. Drainage Density = Drainage Density = total river lengthtotal river length

Basin areaBasin area There are three different drainage densities. There are three different drainage densities.

These are:These are: - Low drainage densities- Low drainage densities - Medium Drainage densities- Medium Drainage densities - High Drainage densities- High Drainage densities

Cont’dCont’d Drainage PatternsDrainage Patterns - arrangement of - arrangement of

streams in a watershedstreams in a watershed Often controlled by geology structures and Often controlled by geology structures and

surface materialssurface materials Reflects the particular plan or design which Reflects the particular plan or design which

individual river courses collectively form.individual river courses collectively form. The most common patterns dendritic, The most common patterns dendritic,

parallel, trellis, rectangular, radial, centripetal parallel, trellis, rectangular, radial, centripetal and deranged or contorted.and deranged or contorted.

Cont’dCont’d Dendritic PatternDendritic Pattern_ Is the most common form _ Is the most common form

and looks like the branching pattern of tree and looks like the branching pattern of tree roots. roots.

Develops in regions underlain by Develops in regions underlain by homogeneous material horizontal sediments homogeneous material horizontal sediments or uniformly resistant rocksor uniformly resistant rocks

Cont’dCont’dParallel Pattern_ develops in regions of

parallel, elongate landforms like outcropping resistant rock bands.

Sometimes indicates the presence of a major fault that cuts across an area of steeply folded bedrock.

Cont’dCont’d Trellis drainage pattern_ develops in folded

topography like that found in the Appalachian Mountains

Tributary streams enter the main channel at sharp angles as they run down sides of parallel ridges called anticlines. ridges called anticlines.

Cont’dCont’d Rectangular pattern found in regions that

have undergone faulting. Movement of the surface due to faulting

offsets the direction of the stream; As a result the tributary streams make shape bends &enter the main stream at high angles.

Cont’dCont’d

Radial pattern -develops around a central elevated Point

Conically shaped features like volcanoes &domes

Cont’dCont’d Centripetal pattern: Centripetal pattern: the opposite of the the opposite of the

radial patternradial pattern Streams flow toward a central depression. This pattern is typical in the western and

southwestern portions of the United States where basins exhibit interior drainage.

During wetter portions of the year, these streams feed ephemeral lakes, which evaporate away during dry periods.

Cont’dCont’d

Cont’dCont’d Deranged drainage : areas recently disturbed

by events like glacial activity or volcanic deposition; many lake and wetland, short streams with few tributaries.

Cont’dCont’d The patterns described above are accordant The patterns described above are accordant

or correlated with the structure and relief or correlated with the structure and relief over which they flow. over which they flow.

Those streams that are discordant with the Those streams that are discordant with the rocks over which they flow are either rocks over which they flow are either antecedent or superimposed.antecedent or superimposed.

Antecedent streams flowed across bedrock Antecedent streams flowed across bedrock structures prior to uplift. structures prior to uplift.

E.g. Columbia River that cuts across the E.g. Columbia River that cuts across the Cascade Mountains.Cascade Mountains.

superimposed streams often not controlled superimposed streams often not controlled by underlying structure because river course by underlying structure because river course established according to structure of established according to structure of overlying strata. overlying strata.

Channel patternChannel pattern Is the configuration of the individual stream Is the configuration of the individual stream

channel as viewed from the air.channel as viewed from the air.

1.Straight Channels Controlled by a linear zone of weakness in

the underlying rock, like a fault or joint system.  

Straight channel does not mean a straight flow.

Velocity is highest in the zone overlying the deepest part of the stream. In these areas, sediment is transported readily resulting in pools.

Sediments are deposited to form bars where the velocity of the stream is low.

Cont’dCont’d 2.Meandering pattern Usually on flat land with unhurried flow with Usually on flat land with unhurried flow with

enough force to erode banksenough force to erode banks Geoscientists use the sinuosity ratio to determine

whether a channel is straight or meandering. Sinuosity ratio is the distance between two points

on the stream measured along the channel divided by the straight line distance between the two points.

If the sinuosity ratio is 1.5 or greater the channel is considered to be a meandering one.

Lateral (sideways) erosion of the river channel Lateral (sideways) erosion of the river channel results in the river forming a winding pattern. results in the river forming a winding pattern.

Cont’d Erosion on outside banks, deposition on Erosion on outside banks, deposition on

inside banks, causing rapid and sometimes inside banks, causing rapid and sometimes abrupt changes in the channel. abrupt changes in the channel.

Cont’d 3.Braided Channels

A network of small channel separated by small and often

temporary islands and bars       A stream that consists of a multiplicity of interwoven

and interconnected shallow channels separated by low

islands of sand, gravel, and other loose debris.

Usually occurs with a very flat stream channel with a heavy load of alluvium and a period of low discharge.

Islands may become resistant to erosion if they become

inhabited by vegetation  

Braided StreamsCont’d

Cont’d Characteristics of channel patternsCharacteristics of channel patterns

Rivers as Agents of Degradation Rivers are one of the greatest sculpturing agents at

work in humid regions. accounts for 85-90% of total sediment transport to the ocean basins (glaciers account for only 7%).

From the source to mouth of a river three processes are taking place.

River erosion River transport River deposition

River ErosionRiver ErosionThere are 4 different ways water erodes the

river away Attrition 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.

Cont’d

See how these rocks are becoming smoother at the See how these rocks are becoming smoother at the edgesedges

The results of attritionThe results of attrition

Cont’d Abrasion (or Corrasion,) is the grinding of

rock fragments carried by the river against the bed and banks of the river.

-This action causes the channel to widen and deepen.

-This grinding is most powerful in flood time when large fragments of rock are carried along in the river bed.

Cont’d An additional process is also at work caused by An additional process is also at work caused by

the force of the water itself known as the force of the water itself known as Hydraulic Hydraulic action.action.

In this rocks are dragged away from the bed In this rocks are dragged away from the bed and banks by the force of the running water. and banks by the force of the running water. 

Corrosion Corrosion is the process by which river water is the process by which river water reacts chemically with soluble minerals in the reacts chemically with soluble minerals in the rocks and dissolves them. rocks and dissolves them.  although this is often called solution – confusing although this is often called solution – confusing

as solution is also a word used in as solution is also a word used in transportation .transportation .

We often say things like water pipes corrode – We often say things like water pipes corrode – the chemicals in the water seem to eat them the chemicals in the water seem to eat them away!away!

Cont’d

Factors of river ErosionFactors of river Erosion VelocityVelocityStream velocityStream velocity – the distance water travels in a stream – the distance water travels in a stream per unit time. per unit time.Velocity is largely controlled by the stream Velocity is largely controlled by the stream gradientgradient, , channel shapechannel shape, and , and channel roughnesschannel roughness.. -Expressed in ft./sec.-Expressed in ft./sec. -The stream reaches its -The stream reaches its maximum velocity near the maximum velocity near the middle of the channelmiddle of the channel.. Velocity is the key factor in a stream’s ability to

erode, transport, and deposit -High velocity – results in erosion and transportation -Low velocity – causes sediment deposition

Cont’dWhen the stream goes around a curve, the region of maximum velocity is displaced by inertia towards the outside of the curve

Cont’dWith in a stream channel, three types of flow can be

observed Laminar flow -Under very low velocities water flows

through a stream as smooth sheets running parallel to the bed In this type of flow the direction of water in the stream is not altered in its direction

Only the finest particles kind be detached, so laminar flow is basically non erosive.

Turbulent flow - under higher flow velocities, resistance within the flow and that caused by the bed and sides of the channel (channel topography) cause the flow to break down into separate currents.

-More erosive than laminar flow and help suspend material in the stream.

- Is the "normal" type of flow in most streams Helical flow - spiral flow in a stream, Caused by

channel shape.

Cont’d GradientGradient– the downhill slope of the stream bed.– the downhill slope of the stream bed. The difference in elevation between two points

on a stream divided by the distance between them

The stream gradient is one of the factors that The stream gradient is one of the factors that controls a stream’s velocity.controls a stream’s velocity.

The steeper the slope, the faster the velocity of flow and the more the energy of the stream will be to erode materials  

Stream GradientStream GradientCont’d

Cont’d Channel Shape and Channel Shape and

RoughnessRoughnessThe The shapeshape of the channel also of the channel also controls stream velocity.controls stream velocity. In wide, shallow channel water flow slowly and in narrow channel it flows rapidly

• The stream in ‘B’ flows slower The stream in ‘B’ flows slower thanthan

‘‘A’ because the wide, shallow channel A’ because the wide, shallow channel in ‘in ‘B’ has more surfaceB’ has more surface for the moving for the moving water to drag against – water to drag against – higher frictionhigher friction.. The The roughness of the channelroughness of the channel also also controls velocity.controls velocity.

Roughness creates more friction Roughness creates more friction and and

slows flow. slows flow.

Roughness of the channelRoughness of the channel

Cont’dChannel shape

Cont’d

In streams in humid climates, In streams in humid climates, discharge discharge increases downstream for two reasons:increases downstream for two reasons:

•as river water evaporates into the air as river water evaporates into the air •and soaks into the dry groundand soaks into the dry ground

In an arid climate, a river’s In an arid climate, a river’s discharge can discharge can decrease in a downstream directiondecrease in a downstream direction

1. Water flows out of the ground into the river 1. Water flows out of the ground into the river through the streambed.through the streambed.2. Small tributary streams flow into a larger 2. Small tributary streams flow into a larger stream along its length, adding water to the stream along its length, adding water to the stream as it travels.stream as it travels.

DischargeDischarge - is the volume of water that flows - is the volume of water that flows past a given point in a unit of time.past a given point in a unit of time.

River TransportRiver Transport A river carries or transports eroded materials such A river carries or transports eroded materials such

as mud, sand, boulders and dissolved materials on as mud, sand, boulders and dissolved materials on its journey. its journey.

These materials are known as These materials are known as its loadits load.. Materials or loads transported by the river can be Materials or loads transported by the river can be

sub divided in to bed Load, suspended load and sub divided in to bed Load, suspended load and dissolved load dissolved load

Bed loadBed load: heavy sediment particles that travel on : heavy sediment particles that travel on the streambed. Such materials include sand and the streambed. Such materials include sand and gravelgravel

These particles may move individually along the These particles may move individually along the bottom, or they may travel in groups. bottom, or they may travel in groups.

They will deposited when ever the local flow They will deposited when ever the local flow conditions will not entrain them. conditions will not entrain them.

Suspended loadSuspended load : are fine or light enough to remain : are fine or light enough to remain lifted indefinitely above the bottom by the water lifted indefinitely above the bottom by the water turbulence. e.g. silts and clays .turbulence. e.g. silts and clays .

Cont’d Dissolved loadDissolved load: : soluble products of chemical soluble products of chemical

weathering process can make up a substantial weathering process can make up a substantial dissolved load in a stream.dissolved load in a stream.

Most streams contain numerous ions in solution. Most streams contain numerous ions in solution. Such as bicarbonate, calcium, potassium, sodium, Such as bicarbonate, calcium, potassium, sodium, chloride, and sulfate.chloride, and sulfate.

Generally, most material is transported in the Generally, most material is transported in the suspended load; the least, in bed loadsuspended load; the least, in bed load

The load is carried along by four processes.The load is carried along by four processes. - - traction traction - - saltation saltation - - suspension suspension -- solution solution TractionTraction is where boulders or stones are rolled or is where boulders or stones are rolled or

sliding along the stream bed by the force of the watersliding along the stream bed by the force of the water

Cont’d

Cont’d SaltationSaltation :t :the speed of the water lifts the he speed of the water lifts the

fragments( fragments( tiny pebbles )tiny pebbles )of the river bottom, and they of the river bottom, and they bounce along bounce along and leapfrog over each otherand leapfrog over each other in a in a process called saltation (from a Latin word meaning process called saltation (from a Latin word meaning jump).jump).

--Saltation, therefore is a combination of traction and Saltation, therefore is a combination of traction and suspension.suspension.

Cont’d SuspensionSuspension is when very fine particles (suspension) is when very fine particles (suspension)

such as clay, silt and fine sand are carried along in such as clay, silt and fine sand are carried along in the river. the river.

--The small particles are held up by the water as they The small particles are held up by the water as they float because they are very, very small!float because they are very, very small!

Cont’dAn example of suspensionAn example of suspension

Cont’d Transportation in Transportation in solutionsolution is when dissolved materials is when dissolved materials

containing minerals like calcium and sodium are containing minerals like calcium and sodium are carried in the water and are invisible to the naked eye.carried in the water and are invisible to the naked eye.

--No picture here because you cannot see them!No picture here because you cannot see them!

Time in transport will round transported grains &decrease size

Cont’d

River DepositionRiver DepositionA river drops A river drops its loadits load when the speed or volume of the when the speed or volume of the

river decreases or river decreases or competence is reducedcompetence is reduced. . CompetenceCompetence - the size of the largest particle that can - the size of the largest particle that can

be transported by a stream. be transported by a stream. CapacityCapacity - the maximum load that a stream could - the maximum load that a stream could

transport under given conditions; its potential.transport under given conditions; its potential. -The heavier material is deposited first and the finer -The heavier material is deposited first and the finer

material carried further.material carried further. -Rivers reduce their speed when they enter flat land, -Rivers reduce their speed when they enter flat land,

enters a lake or the sea or reach an arid area or enters a lake or the sea or reach an arid area or with with change in gradient or as channel widens or changes change in gradient or as channel widens or changes direction. direction.

-The volume can be reduced during a dry season or -The volume can be reduced during a dry season or when the river passes over more porous landscapes when the river passes over more porous landscapes e.g. sand or limestone.e.g. sand or limestone.

Cont’d Some of the depositional land forms include

levees ,flood plain, delta, alluvial funs , back swamp, point bars and etc.

-The details of these features will be discussed in the fallowing section.

-materials deposited by river are known as Alluvium. -Most alluvium is deposited into quiet water (ocean or

lake).

River valley development and River valley development and associated land forms   associated land forms  

Streams develop their valley through the fallowing ways;

1.Down cutting1.Down cutting – the process of deepening a – the process of deepening a valley by erosion of the streambed.valley by erosion of the streambed. If a stream removes rock from its bed, it can If a stream removes rock from its bed, it can

cut a narrow slot canyon down through the cut a narrow slot canyon down through the rock.rock.

Such canyons are not common because down Such canyons are not common because down cutting is usually is usually accompanied by cutting is usually is usually accompanied by mass wasting and sheet erosion of the valley mass wasting and sheet erosion of the valley wallswalls..

The limit of down cutting is known as base level; it is a theoretical limit for erosion of the earth’s surface

Cont’d

Cont’d2.Lateral erosion: a2.Lateral erosion: a

stream can de stream can de deepening its channel deepening its channel by cutting while part of by cutting while part of its energy is also its energy is also widening the valley bywidening the valley by lateral erosion.lateral erosion.

The erosion of a The erosion of a stream’s bank and stream’s bank and valley walls as the valley walls as the stream swings from side stream swings from side to side across its valley to side across its valley floor.floor.

Cont’d3.Head ward erosion3.Head ward erosion :a stream can also lengthen its :a stream can also lengthen its

valley by hvalley by head ward erosionead ward erosion.. The slow uphill growth of a valley above its The slow uphill growth of a valley above its

original source through gulling, mass wasting, original source through gulling, mass wasting, and sheet erosion.and sheet erosion.

Stream capture (Stream piracy) Stream capture (Stream piracy) - - an event where a an event where a portion of the flow of one stream is diverted into that portion of the flow of one stream is diverted into that of another by natural processes.of another by natural processes.

Cont’d A.A. Graded stream Graded stream Has regulated its various stream parameters

(depth, width, slope, velocity, etc.) to obtain the most efficient conditions for flow and sediment transport.

A graded stream is capable of maintaining a steady-state condition.

Characteristics of a graded stream

Slope of the longitudinal profile is concave upward, steeping upstream.

No falls or basins exist within the channel profile. No net erosion or deposition occurs along its

channel. The stream is capable of handling all sediment

introduced to it from its tributaries.

Cont’d B. Non-graded stream Energy within the system is not evenly distributed Energy within the system is not evenly distributed

along the profile; contains falls and basins.along the profile; contains falls and basins. Falls result in a concentration of energy, which Falls result in a concentration of energy, which

promotes erosion.promotes erosion. Basins result in a decrease in energy, which Basins result in a decrease in energy, which

promotes deposition.promotes deposition.

Young Stage-Has steep-sided and narrow V-shaped valley created by vertical erosion-characterized by waterfalls and rapids. -Water is often quite clear because the river is not carrying much load in suspension. -Velocity is high.-Down cutting and head ward erosion are the major processes of river erosion.

and and head wardhead ward erosion is dominanterosion is dominant

Cont’d Valley profile in the upper courseValley profile in the upper course

V shape valley

Long Profile o f a typical stream 

 

Is a depiction of the down slope gradient of stream. 

Gorge  A gorge is a steep, V-shaped valley formed

by the vertical (down ward) erosion of the land by the river.

The Indus Gorge in Kashmir is the deepest in the world (about 5180 m.).

If the region is arid where there is little weathering and mass wasting on the valley sides, the gorge will be impressively deep. If such a gorge is deep, long and U-shaped, we call it canyon.

Cont’d In the case of a canyon the valley is

deepened more than they are widened.

Slot-canyon: Young stream, eroding down and no mass wasting

Cont’d Water fallWater fall : a steep drop in the course of a river. It has a high head of water and a characteristic

Plunge pool at the base. Waterfalls often form when a band of resistant

rock lies over softer, less resistant rocks. Knick point- a sharp irregularity in a stream-

channel profile, commonly caused by abrupt changes in bedrock resistance and at which Waterfalls starts.

Plunge pool : also known as a waterfall lake Is a pool, lake, or pond that is small in diameter,

but deep. Plunge pools can remain after the waterfall has

ceased to exist or the stream has been diverted.

Cont’d

-Cap Rock - layer of hard resistant rock forming the 'step' over which the 'falls' occur in a waterfall.

Water fallWater fall

Tis Isat” (Blue Nile) Waterfall

Cont’d

Potholes Are depressions that are eroded in to the

land rock of the streambed by abrasive action of the sediment load.

When a stream is full, the swirling water can cause sand and pebbles to scour out smooth, cylindrical or bowl- shaped depression in hard rock.

Tend to form in spots where the rock is a little weaker than the surrounding rock.

They may contain certain sand or an assortment of beautifully rounded pebbles.

PotholesCont’d

spurs are ridges of more resistant rock around which a river is forced to wind as it passes downstream in the upper course.

Interlocking spurs form where the river is forced to swing from side to side around these

Interlocking Spurs

Interlocking SpursInterlocking Spurs

River channel

Cont’d

Maturity stage Many tributaries have fed the river upstream. The volume of water increases and lateral erosion is

taking place River channel has become much wider and deeper The surrounding valley has also become wider and

flatter with a more extensive floodplain.

Bends or loops in the river One of the most distinctive features of the river in the

middle course is its increased sinuosity. Unlike the relatively straight channel of the upper

course, in the middle course there are many meander (bends) in the river.

Meanders

Cont’dAs water flows into a meander it takes on a

helical or spiral flow that determines where erosion and deposition is concentrated.

Centrifugal force draws water toward the outside bank causing erosion and creates a bend . Sediment eroded from the outside bank is deposited on the inside bank

Slip off Slope - a small beach found on the inside of a meander bend where deposition has occurred in the low energy zone.

River Cliff - a small cliff formed on the outside of a meander bend due to erosion in this high-energy zone. when the water in an ox-bow lake dries

Cont’d

Cont’d

Neck & Cutoff Neck Is the upland between tow consecutive

(opposing) meanders of a stream. Cutoff or an Oxbow :occurs when the neck

between river meanders is totally eroded away and the meanders join to shorten the length of the channel.

1. A gently meandering river flows through an area of relatively flat terrain.

2. Water flows at different speeds as it goes around bends in a meandering river. On the outside banks of corners, the river water moves the fastest, causing lateral erosion and undercutting

3. Meanwhile, on the inside banks of corners in the river, the water flows more slowly, leading to sediment settling out of the water & building up on the inside banks.

Cont’d4.4.Gradually, the inside banks are filled in with Gradually, the inside banks are filled in with

accumulated deposits, and the outside bends accumulated deposits, and the outside bends extend further and further, forming a wide loop extend further and further, forming a wide loop in the river.in the river.

5.5.The loop continues to bend further and further, The loop continues to bend further and further, until a thin strip of land called a neck is created at until a thin strip of land called a neck is created at the beginning and the end of the meander the beginning and the end of the meander

6. Eventually, the narrow neck is cut through by either gradual erosion or during a time of flooding. When this happens, a new straighter channel is created, diverting the flow of the river from the loop into the new channel.

7. Deposition finally seals the cut-off from the river Deposition finally seals the cut-off from the river channel, leaving a crescent-shaped land form channel, leaving a crescent-shaped land form known as oxbow lake. known as oxbow lake.  

Meander scar - feature left behind when the water in an ox-bow lake dries up

Oxbow Lakes

Oxbow Lakes

Meander neck becomes smaller

new course of the river

oxbow lake

When the river floods it breaks through the thin meander neck and the river takes the easier, straight course. This leaves the meander loop ‘cut off’ as an oxbow lake. Over time, the oxbow lake will become colonised by vegetation.

Old Stage Final stage of a river is reached when the river is

flowing on more or less flat surface. The speed so low that no net erosion occurs any

more. Erosion on the slopes is balanced by deposition on

the floodplains. Peneplain -a flat and relatively featureless landscape

with minimal relief; considered to be the end product of the geomorphic cycle. Peneplain means “almost a plain. The process is known as peneplanation

From now on the rivers just sweep over the floodplain and rework the sediment, creating various floodplain features. Isolated remnants of resistant bedrock may rise over the Peneplain surface, the so-called monad nocks or inselbergs.

Yazoo stream _ a tributary unable to enter the main stream because of natural levees along the main stream; instead flows downstream to the back swamp zone and runs parallel to the main stream until it finds an entrance.

Rejuvenation Old or mature stage landforms may be uplifted due to

climate change or tectonic activity Entrenched meanders are the result.     Entrenched meander :a winding, sinuous stream

valley with abrupt sides. In a fashion, the landscape reverts to an earlier stage

in its evolution (e.g. from intermediate/mature to the initial/young stage

Cont’d

Cont’d Because the river is moving on a flat surface,

deposits sediments at the bed often act as barriers to free flow of water making it to form meanders.

The meander, in this case, does not, however, occupy the whole valley bottom as in the case of the middle course

Point BarIs a depositional feature of streams. Point bars are found in abundance in mature or

meandering streams. Point bars are composed of sediments that are well stored and typically reflects the overall capacity of the stream.

Point bar deposits on the inner meander bend where there is low energy

Deposition and Erosion of River BarsDeposition and Erosion of River Bars

Flood: Increaseddischarge anderosion!

Normal Flow

Post-flood; newbars deposited

Floodplain  A relatively flat area that borders a stream, which

is periodically inundated with water during high flow periods.

The resulting decrease in velocity causes sediment carried by the stream, such as gravel, sand, silt, and clay, to deposit as alluvium on the floodplain.

Large particles are deposited first, and much of this material is laid down alongside both banks.

Bluff : a relatively steep slope at the outer edge of a floodplain, marking the outer limit of lateral erosion and undercutting.

Flood plainFlood plainCont’d

Bluff

Natural levee is a narrow ridge of alluvium deposited at the side of the

channel. During high discharge periods when the stream floods, coarse sediment settles out near the stream channel and grades to finer material further away.

Back swampsBack swamps Located some distance away from the stream Located some distance away from the stream

channel on the floodplain. channel on the floodplain. When water spills over onto the floodplain, the When water spills over onto the floodplain, the

heaviest material drops out first and finest material heaviest material drops out first and finest material is carried a greater distance. is carried a greater distance.

The fine-grained alluvium holds much water and The fine-grained alluvium holds much water and drains rather slowly creating wetland areas.drains rather slowly creating wetland areas.

important "sponges" that retain water that might important "sponges" that retain water that might cause severe flooding downstream. cause severe flooding downstream.

Land forms produced by river

Cont’d

Stream terraces Are elevated portions of a floodplain created

when the stream down cuts and creates a new floodplain at a lower elevation.

Paired terraces

Occur at same elevations on opposite valley sides; produced by intermittent down cutting with changes in discharge , load or base level.

Unpaired terraces Fragment of former floodplain “accidentally”

preserved (e.g. by a rock buttress) as a meandering stream slowly degrades it

Stream TerraceStream Terrace

Stream terraces

DeltaDelta A landform at the mouth of a river produced. A landform at the mouth of a river produced.

by the sudden dissipation of stream’s by the sudden dissipation of stream’s velocity and the resulting deposition of the velocity and the resulting deposition of the stream’s load.stream’s load.

Distributaries: branching stream channel that Distributaries: branching stream channel that crosses a delta crosses a delta

For the formation of a delta the following For the formation of a delta the following necessary conditions should be fulfilled. necessary conditions should be fulfilled.

-large load, -large load, -low velocity and-low velocity and -loads must be deposited faster than it -loads must be deposited faster than it

can be removed by the action of tides& can be removed by the action of tides& currentscurrents

Cont’d The shape of a delta depends on following factors The shape of a delta depends on following factors the rate of sediment supply,the rate of sediment supply, wave action and coastal currents reworking the wave action and coastal currents reworking the

deposited sediment,deposited sediment, and the rate at which the alluvial deposits and the rate at which the alluvial deposits

subside. subside. We have four basic types of delta. These are:We have four basic types of delta. These are: --Arcuate Arcuate --Bird footBird foot -- Cuspate Cuspate -- Estuarine Estuarine

1.Arcuate Delta1.Arcuate Delta Fan or inverted cone-shaped delta .Fan or inverted cone-shaped delta . Has many active, short distributaries Has many active, short distributaries

taking coarse and fine sediment to their taking coarse and fine sediment to their mouths. mouths. 

In areas of significant wave activity sediment will be redistributed laterally along the delta front to forma smooth arcuate shoreline with many sand bars, beach ridges and/or barrier islands.

ExamplesExamples : :Nile, the Ganges, the Indus, the Nile, the Ganges, the Indus, the Irrawaddy, the Mekong and the Hwang – Irrawaddy, the Mekong and the Hwang – Ho.Ho.

Arcuate Delta

2.Bird’s foot Delta Where delta formation is river-dominated and less

subject to tidal or wave action, a delta may take on a multi-lobed shape which resembles a bird’s foot.

Tend to have one or a very few major distributaries near their mouths.

It consists of very fine martial, called silt. There is a broad, shallow shelf that deepens abruptly, so the trend is to grow long and thin like a bird's toe.

Example; -Mississippi Delta and

Bird’s foot Delta

3.  Cuspate Delta3.  Cuspate Delta

Tooth-shaped delta Tooth-shaped delta Formed by a river that usually has one Formed by a river that usually has one

distributaries' emptying into a flat coastline with distributaries' emptying into a flat coastline with wave action hitting it head-on. wave action hitting it head-on. 

This tends to push the sediment back on both This tends to push the sediment back on both sides of the mouth, with a "tooth" growing out sides of the mouth, with a "tooth" growing out onto the shelf. onto the shelf.

Example; -Tiber River of Italy -Tiber River of Italy -The delta of Niger River -The delta of Niger River 

Cuspate DeltaCuspate Delta

Tiber River delta of ItalyTiber River delta of Italy

4.  4.  Estuarine DeltaEstuarine Delta

Developed when a river that empties into a long, Developed when a river that empties into a long, narrow estuary that eventually becomes filled with narrow estuary that eventually becomes filled with sediment (inside the coastline).sediment (inside the coastline).

Examples of this type of delta include ;Examples of this type of delta include ; -The delta of Seine River of France -The delta of Seine River of France -The deltas of the River Vistula (in Poland) and-The deltas of the River Vistula (in Poland) and -The Ob river (USSR) -The Ob river (USSR)

Estuarine Delta

Are fan-shaped alluvial deposits generally found when a mountain stream runs on to a flatter surface at the front of a mountain system. Mountain streams carrying a heavy stream load loses their kinetic energy as they flow out on to the flat plain depositing alluvium. Alluvial fans are quite common in arid regions where water is lost to evaporation and infiltration into coarse surface material when the stream exits the mountain front.

Alluvial fans

Alluvial fans

Alluvial Fans - Brooder Peninsula, Baffin Island, Canada.

Bajada_ forms when several individual alluvial fans merge into one broadly sloping surface.

Cont’d

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