chapter 11: fluvial processes, patterns and landforms, and human interaction rivers transform the...

Chapter 11: Fluvial Processes, Patterns and Landforms, and Human Interaction

RiversTransform the landscape in three main ways:

1. Erosion – wearing it away2. Transportation – moving its load downstream3. Deposition – dropping its load


Important terms• Load – a river transports eroded material• Source – where a river begins• Course – the route a river takes as it flows from

an upland area down through its valley until it enters the sea

• Tributary – a stream/river which joins a larger river

• Mouth – the place where a river enters the sea or lake


Important terms (continued)• Estuary – where a river mouth is tidal• River basin – the entire area which is drained by

a river and its tributaries• Watershed – the high ground that separates two

river basins• River discharge – the amount or volume of water

carried by a river at a given time


Rate of river erosionDepends on the following:

• Size• Speed• Hardness of the rock the river flows over


The velocity/speed of a riverInfluenced by:

• Gradient • Volume of water carried by river • Roughness of the channel • Shape of river channel


Processes of fluvial erosionRivers erode through a number of processes:

• Hydraulic action• Abrasion/corrasion• Solution/corrosion• Attrition


Different types of erosion in a river channel• Vertical – river erodes down into riverbed• Lateral – river erodes the sides of the river

channel• Headward – erosion backwards of material at

the river source


Processes of transportationRivers transport their load by four processes:

1. Solution2. Suspension3. Saltation4. Traction


River depositionDeposition is the dropping of the river’s load. Rivers

deposit their load when the following occurs:• The river loses speed• There is a reduction in waters in the river channel• The river flows into a lake or sea• The slope or gradient of the river is reduced• The river flows over a permeable rock layer, which

allows the water to pass through easily• The river is carrying a larger load than it can

actually transport


River profileThree stages can be identified:

• Youthful or upper river valley• Mature or middle river valley• Old age stage or old river valley


1. Youthful stage• Processes of erosion are active • River cuts down into the riverbed –

referred to as vertical erosion


Features of youthful riverI. V-shaped valley

• Formed in the youthful stage of a river valley• Vertical erosion deepens valley floor• Hydraulic action loosens and dislodges rock• The river’s load further erodes and abrades the

valley• Deepens the riverbed and creates steeper sides• Sides are then weathered• Mass movement causes the sides of the valley to

move downslope into the river


Features of youthful riverI. V-shaped valley (continued)

• Processes of transportation move material down river

• Valley with steep sides and narrow floor remains• Interlocking spurs may form• Areas of high ground that jut out from each side

of the valley where river meets resistant hard rock; it is unable to erode

• River flows around the hard rock while still eroding downwards

• Creates a series of interlocking spurs


Features of youthful riverII. Waterfall

• Formed in the youthful stage of a river valley• Channel is narrow and deep• Created where a band of hard rock lies next to a

layer of soft rock• Differential erosion occurs• Soft rock is eroded and transported downstream.• Leaves hard, more resistant rock elevated and

standing out• As the process continues the drop over the more

resistant rock becomes steeper• Flow over the resistant rock forms a waterfall


Features of youthful riverII. Waterfall (continued)

• A series of rapids are often formed above the area of resistant rock

• Processes of hydraulic action and abrasion• A plunge pool forms at the base of the waterfall• Deepens as a result of hydraulic action and abrasion• Back wall of the waterfall will be further eroded as a

result of the water spray eroding the soft rock• Soft rock is eroded and the remaining hard rock is

left exposed• Hard, resistant rock eventually falls into the bottom

of the waterfall


2. Mature stage• Less steep than that of a youthful river valley• River flows more slowly • Many tributaries join• More discharge• River erodes laterally


Features of mature river I. Meanders

• Volume of water and the river’s load increases• Water on the outer bend of a meander is deep;

the river moves faster and erosion occurs• Water on the inner bend of a meander is shallow;

the river moves slowly and deposition takes place • River cliff• River beach or point bar


3. Old stage• River is moving very slowly• Level low-lying ground• River has very little energy to erode• The river deposits its load which has become

too heavy to transport


Features of old river I. Floodplains

• Linked to the formation of a meander• River meanders and swings from side to side; a

wider flat valley floor is formed• Following a heavy bout of rain, the volume of

water increases within the river channel flooding out over the flat land

• Finest, lightest particles of the river’s load carried by suspension away from the river channel

• Alluvium deposited on the floodplain


Features of old river (continued)II. Oxbow lakes

• Formed when a meander is cut-off from the river• Lateral erosion takes place on the outer bend • Deposition occurs on the inside bend• After a long period of time meander neck becomes

very narrow• Narrow neck is eventually cut through• River at the cut-off point has very little energy• Deposits its load leaving a meander loop isolated• Oxbow lake is eventually formed when deposit

seals off both ends of the cut-off meander loop • Eventually oxbow lake dries up forming a

mortlake


Features of old river (continued)III. Levees

• River loses energy • It moves out of original river channel and flows

over a wider floodplain• Speed is reduced and its ability to transport is

also reduced• Deposition occurs• Heavy material is deposited first whilst lighter

material flows further out over the floodplain• Over time, the deposition of coarser material

along the riverside leads to the formation of raised banks


Features of old river (continued)IV. Deltas

• Formed at the mouth of a river where the river enters an estuary, sea or lake

• River loses speed and its energy to transport recedes• Deposition of alluvium• Alluvium build ups and become visible above the

water• Bottomset beds are composed of fine deposits – are

carried/transported out furthest to sea• Foreset beds are composed of coarser deposits – are

deposited close to the river mouth• Topset beds are composed of differing deposited

material – some fine, some coarser, e.g. silt and sand


Features of old river (continued)IV. Deltas

• Lacustine deltas form where rivers enter lakes• Marine deltas form where rivers enter the sea.

There are three main types of marine delta: Arcuate delta Estuarine delta Bird’s foot delta


River drainage patterns1. Dendritic pattern2. Radial pattern3. Trellis pattern4. Deranged pattern


1. Dendritic pattern• Similar in appearance to a tree• Develops in areas that have rocks of equal

hardness • Develop where the river follows the slope of the

physical landscape• Tributaries join the main river at an acute angle;

less than 90°


2. Radial pattern• Similar in appearance to the spokes of a wheel• Rivers radiate down from a central apex on the

top of a mountain


3. Trellis pattern• Occurs where rivers have tributaries joining the

main river at right angles in areas that have rocks of unequal hardness, i.e. areas of hard and soft rock

• Differential erosion occurs where soft rock is eroded easily and faster than hard resistant rock

• Forms in areas that have experienced folding, such as the Munster Ridge and Valley Province

• The River Blackwater is a river found in this area and its tributaries join onto it at right angles


4. Deranged pattern• Occurs where glaciation has impacted on the

landscape• Rivers are irregular in their pattern/appearance


Impact of human activity on river processes1. Hydro-electric dams

Positive• Generation of electricity• Supply of water• Controlling the effects of flooding• The reservoir can be used for recreational

purposes and also for aquaculture

Negative• Relocation of people• Natural flooding does not occur down river• Reduction in the number of species living in the

river ecosystem


Impact of human activity on river processes2. Canalisation

Positive• Efficient water transport• Irrigation purposes• Flood control measures – levees

Negative• River bank failure • Flooding elsewhere along the river course


The River Rhine case study• One of the longest and most important rivers in

Europe• Length approximately 1,232 km (766 miles)• Source in the Swiss Alps• Flows through six countries: Switzerland,

Liechtenstein, Austria, Germany, France, the Netherlands

• Enters the North Sea at Rotterdam, the Netherlands

• Main tributaries are the Main, Necker and Moselle


Features• One of the main traffic arteries of Western

Europe• An important means of transporting and shipping• Canal network developed around the river course• Dykes constructed to prevent the likelihood of

flooding• Meanders bypassed by the construction of new

canals and channels• Resulted in a shorter, deeper and straighter river

course


Impact of changes to river courseDykes

• Land is utilised for agricultural purposes and buildings have also been constructed on the floodplain

• Dykes have been constructed and are regularly increased in size to protect the surrounding agricultural land and buildings

• Prevent the river flooding over its banks at dyke locations resulting in flooding being transferred further downriver

• River cannot deposit onto its floodplain and so deposits sediment onto the river bed

• Raises the level of the river• Dykes must be regularly upgraded to match the new

river height


Impact of changes to river courseShipping

• Areas of the River Rhine were narrowed to create a deeper river channel to allow larger ships to travel through

• Rhine travels through polders in the Netherlands between high embankments

• Embankments absorb water• Embankments may eventually collapse resulting

in the surrounding land being flooded


Impact of changes to river courseHEP

• Thirteen hydroelectric power stations constructed along the river

• Contributed to increased flooding along the course of the river

• Power Project involved the construction of a new section of river running parallel to the old River Rhine course


Outcome of changes to river course• Dams trap sediment, which reduce the rivers

load• Created a faster and deeper river• Flooding frequency and water flood levels

increased over the last 100 years• Plan to tackle the problem by restoring 100

artificial channels and 11,000 km of river bank

chapter 11: fluvial processes, patterns and landforms, and human interaction rivers transform the...

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