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Bellwork Complete your mini quizzes (to test your OWN knowledge, not the knowledge of the person sitting next to you)

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Presentation on theme: "Bellwork Complete your mini quizzes (to test your OWN knowledge, not the knowledge of the person sitting next to you)"— Presentation transcript:

1 Bellwork Complete your mini quizzes (to test your OWN knowledge, not the knowledge of the person sitting next to you)

2 Rivers Quiz 1.What is evapotranspiration? 2.What is the equation for working out precipitation? (Clue- it includes the following: S=Storage, E=Evapotranspiration, O=Total Runoff (Streamflow)) P= 3.Is groundwater storage found above or under the ground? 4.What is river discharge measured in? 5.What is lag time?

3 Rivers Quiz 1.What is evapotranspiration? 2.What is the equation for working out precipitation? (Clue- it includes the following: S=Storage, E=Evapotranspiration, O=Total Runoff (Streamflow)) P= 3.Is groundwater storage found above or under the ground? 4.What is river discharge measured in? 5.What is lag time?

4 Answers! 1.What is evapotranspiration? Evaporation + Transpiration 2.What is the equation for working out precipitation? (Clue- it includes the following: S=Storage, E=Evapotranspiration, O=Total Runoff (Streamflow)) P= O+E+/-S 3.Is groundwater storage found above or under the ground? Under the ground 4.What is river discharge measured in? cumecs 5.What is lag time? The amount of time in between peak rainfall and peak discharge

5 River Processes Learning Objectives: To understand river processes and the Hjulström Curve Learning outcomes Name the 4 erosional processes Name the 4 transportational process Interpret the Hjulström curve

6 River Processes Erosion Hydraulic Action Corrasion/Abrasion Attrition Solution/Corrosion Transportation Traction Saltation Suspension Solution Deposition Low river energy

7 RIVER PROCESSES: Three river processes: 1.Transportation 2.Deposition 3.Erosion

8 Information Hunt Walk around the room to find the information about the 3 main river processes in order to complete your sheet *Extension Task- Draw a diagram to go with each of the definitions*

9 Solution minerals are dissolved in the water and carried along in solution.

10 Saltation small pebbles and stones are bounced along the river bed.

11 Suspension fine light material is carried along in the water.

12 Traction large boulders and rocks are rolled along the bed of the channel.

13 Hydraulic Action Air may become trapped in joints and cracks on a river bank. When a wave breaks, the trapped air is compressed which weakens the bank and causes erosion.

14 Attrition Fast river discharge causes rocks and pebbles that are suspended in the water to crash into one another into each other, and they break and become smoother.

15 Abrasion/Corrasion Bits of rock and sand in waves grind down river channel surfaces like sandpaper.

16 Solution/Corrosion Acids contained in water will dissolve some types of rock such as chalk or limestone.

17 Deposition Deposition of bedload when river discharge is low can form river beaches/slip off slopes

18 River Processes ErosionTransportationDeposition Erosion usually happens in 4 different ways and forms river cliffs and waterfalls Attrition: Solution/Corrosion: Abrasion/Corrasion: Hydraulic Action: Transportation is the process whereby bed load is carried down the long profile of the river towards the sea Traction: Saltation: Suspension: Solution:

19 River Competence & River Capacity River Competence is the maximum size of load a river is capable of transporting. River Capacity refers to the total volume of sediment a river can transport. It is important to note that the velocity has an influence: –At low velocity only fine partials may be transported (Clays, silts, and sands). –At a higher velocity larger material can be moved. Maximum particle mass that can be moved increases with the power of velocity, so when discharge levels are high (during a flood for example), much larger boulders can be moved.

20 Hjulstrom Curve River Processes

21 Hjulstrom curve The Hjulstrøm curve is a graph used by hydrologists to determine whether a river will erode, transport or deposit sediment. The graph takes sediment size and channel velocity into account. The curve shows several key ideas about the relationships between erosion, transportation and deposition.

22 Hjulstrom curve The Hjulstrøm Curve shows that particles of a size around 0.5 mm require the least energy to erode, as they are sands that do not coagulate (such as clay). Particles smaller than these fine sands are often clays which require a higher velocity to produce the energy required to split the small clay particles which have coagulated.

23 Hjulstrom curve Larger particles such as pebbles are eroded at higher velocities and very large objects such as boulders require the highest velocities to erode. When the velocity drops below this velocity, particles will be deposited or transported, instead of being eroded, depending on the river's energy.

24 THE HJULSTRÖM CURVE The hjulström curve illustrates the relationship between velocity and competence. It shows the velocities at which sediment will normally be eroded, transported or deposited. Very fine particles need higher velocity to erode them than larger particles as materials like clay and sand are cohesive. Less energy is needed here to erode a particle as less energy is needed to erode sands than clays. Some of the smallest particles can stay in suspension when the water is still When the particles are boulders, even the smallest drop in velocity can mean they are deposited.

25 Drawing the Hjulström Curve In order to aid your understanding of what the Hjulström curve is showing, copy out your own version for your notes, noting carefully the logarithmic scale on the x axis

26 Hjulstrom Curve River Processes

27 Hjulstrom Curve River Processes

28 Words Fill! eroded 0.1 silt 120 transported 150 cobbles 200 At 10 cm per second has eroded whilst would be deposited. The smallest clay particles require velocities of cm per second to be eroded. For the smallest silts it is approximately cm per second. Cobbles are upwards of 170cm per second. Deposition starts to occur at cm per second for particles of approximately 0.01mm in size. Boulders require the smallest velocity for deposition, at only cm per second for the smallest boulders 250mm in size. Course sand of 0.5 mm in size is between 3cm per second and 16 cm per second. silt cobbles eroded transported

29 Plenary Critique How could we critique the Hjulstrom curve?


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