1. The water cycle

4. The drainage basin

5. river evapotranspiration precipitation throughflow surface runoff groundwater flow water table interception percolation infiltration The drainage basin

7. Long Profile Height above sea level in meters.0 50 100 150 200 250 35 30 25 20 15 10 5 0 Distance from sea in Kms. Source. Upland stream. Lowland river. Mouth. Gradient/slope decreasing Velocity/flow increasing Cumecs/discharge increasing Energy increases

8. In upland areas rivers are high above their base level (The lowest limit to which erosion can take place). This means the river have lots of potential energy As the river descends in height it speeds up – increasing its energy. Rivers realise their full potential energy by reaching maximum velocity (fastest rate of flow). Rivers realise their full potential energy by reaching maximum velocity (fastest rate of flow). Rivers therefore use surplus energy to allow fastest flow

9. In order to reach their maximum flow rivers seek to achieve minimal resistance to their flow. Put simply to flow faster they must overcome FRICTION

10. Most friction/resistance comes from the wetted perimeter The wetted perimeter is where the water comes into contact with the river’s bed and banks. A river will use any spare energy it has to overcome this resistance by seeking to change the shape of the channel via erosion (making it smoother). Energy is also used to clear the channel of any debris, including that which has been eroded as this to causes friction – so material is also transported down the river The faster the flow the more energy is available for erosion and transportation

12. In upland areas the channel is often filled with large boulders that causes friction and reduces velocity (at this stage there is not enough energy to erode these boulders) The further you move from the source the more energy the river will have to overcome friction via increased water, thus the faster it will flow. Reduced bed load will also allow velocity to increase

13. The river channel also continually works to reach its base level As a result it will use energy to erode vertically in the steeper upland sections. As the river begins to reach its base level more energy is available for lateral erosion (sideways)

14. Long Profile Recap Gradient? Channel Depth? Channel Width? Velocity? Why does it change?

15. ENERGY ENERGY

16. DESCEND= SOME ENERGY= EROSION= REDUCED FRICTION=FASTER FLOW = GREATER ENERGY= MORE EROSION=REDUCED FRICTION FASTER FLOW= GREATER ENERGY=MORE EROSION =REDUCED FRICTION=FASTER FLOW= GREATER ENERGY=MORE EROSION etc

17. Friction can be reduced further and energy increased by the addition of more water into the channel – this occurs as you move down the long profile

18. Long Profile Height above sea level in meters.0 50 100 150 200 250 35 30 25 20 15 10 5 0 Distance from sea in Kms. Source. Upland stream. Lowland river. Mouth. Gradient/slope decreasing Velocity/flow increasing Cumecs/discharge increasing Energy increases

20. HOW DOES A RIVER ERODE AND TRANSPORT MATERIAL?

21. Processes of Erosion Attrition (material collides with each other) Abrasion (sandpaper on bed and banks) Solution/Corrosion (acids dissolve) Hydraulic Action (force)

22. Key Words - Erosion. Attrition – where material is moved along the bed of a river, collides with other material, and breaks up into smaller and smaller pieces. Corrasion/Abrasion – fine material rubs against the river bank. The bank is worn away, by a sandpapering action. Corrosion/Solution – some rocks forming the banks and bed of a river are dissolved by acids in the water Hydraulic action – the sheer force of water hitting the banks of the river.

23. Transportation. Transportation. Traction – where large rocks and boulders are rolled along the river bed. Saltation – where smaller stones are bounced along the river bed in a leap frogging motion Suspension – where very small grains of sand or silt are carried along with the water Solution – where some material is dissolved (like sugar in a cup of tea) and is carried downstream.

24. Traction Heavy rocks and boulders are rolled along the river bed. Happens most in times of flood, when the current is strongest.

25. Saltation. Small stones and pebbles are ‘bounced’ along the river bed. Saltation can take place when the river flow is less than that needed for ‘Traction’ to take place.

26. Suspension Very small particles of sand or clay that are ‘suspended’ in the water. These particles will ‘settle’ if kept in a jar of water overnight and the water will look clear.

27. Solution. Takes place when material is dissolved in the water, it is invisible and does not colour the water. Some pollutants like weedkiller are also held in solution in the water

28. Landforms in the upper course V-shaped valleys and interlocking spurs RapidsWaterfalls

29. river disappears from view hidden by this spur of land Upper Valley - River Conwy (near Mignant Moor) Landforms in the upper course

36. Rapids

37. Identify v-shaped valleys and spurs of land from this OS map

39. What happens to the river when it moves to the middle course? Gradient becomes less steep River continues to erode vertically but LATERAL erosion now occurs. River channel is changing shape River channel becomes more efficient Spare energy Eroded material picked up and transported Meanders and Ox-bow lakes form

40. Stages in the Development of a River Valley

41. The river cuts downward to form a ‘V’shaped valley. The river starts to meander

42. River uses its meanders to cut from side to side eating into the valley Floodplain starts to form 1 2

43. 1 2

44. Floodplain River bluffs River cliff Alluvial deposits

45. It changes from this…..

46. To this…….

47. What is here? Where did this material come from? Does the river flow faster or slower here? Why is the material dropped here? The inside bend

48. About how high the river bank here? Is the river flowing faster or slower here? What is the river doing to the bank here? The outside bend

49. Valley bottom and flood plain Valley sides River meander River beach Eroded bank River channel

51. Future changes Erosion on the outside bend Deposition on the inside bend River meander moves downstream

56. Oxbow lakes Meander loops

58. LEVEES

59. 1.Floodplains and levees are formed by deposition in times of river flood. 2.When there is a lot of water in the river channel the river is flowing at a faster velocity. 3.As a result it can transport a large load 4.However when the water floods over the channel banks it quick looses its velocity (due to increased wetted perimeter) 5.The river therefore deposits its load. 6.It will deposits the heaviest of these particles first (as they need the greatest amount of energy to be transported.) 7.These larger particles, often pebble-sized, will build up close to the river channel to form leveés. 8.The sands, silts and clays are similarly sorted with the sands being deposited next, then the silts and finally the lightest clays. This deposition makes up the floodplain. Floodplain formation

60. Floodplains

63. 1.As the river meets the sea there is a sudden drop in velocity 2.This drop means the river is suddenly unable to carry as much load and so deposition occurs. 3.As with levees the deposition is graded. 4.The top of the delta is a fairly flat surface. 5.This is where the coarsest river load is dropped. 6.The finer particles are carried into deeper water. 7.The silt is dropped to form a steep slope on the edge of the delta while the clay stays in suspension until it reaches the deeper water. silt clay sand Delta formation

65. Estuaries

66. Long Profile of a River 1. The land is flat on either side of the river and is easily flooded at high tide 2. The valley sides are flatter here 3. The valley sides are very steep and there may be a waterfall on this section of the river 4. The river has formed wide sweeping bends called meanders. 5. The river looks as though it is flowing very fast in this section because the gradient is steep and the bed of the river has large angular boulders 6. The river valley has interlocking spurs 7. The river is eroding laterally in this part of the river rather than vertically, 8. The gradient of the river is gentler and the channel is wider. 9. The river is flowing at its fastest at this point 10. The bed of the river has small rounded pebbles and fine silt 11. Tributaries, surface run-off and ground water have increased the volume of the river 12. The river is deep here

67. The causes and effects of flooding River basin management issues The causes and effects of flooding in MEDC and LEDC The short, med and long term strategies used to manage floods ‘Hard’ and ‘Soft’ strategies to manage rivers River basins often need to be managed to supply water as well as manage flooding

70. Flood Management Floods occur when discharge exceeds bankfull capacity. Water leaves channel to cover adjacent land – the flood plain. Human occupancy of this flood zone creates need for hazard response.

71. Human Impact on Run-off and flooding Most activity tends to increase flood risk by reducing the interception store and thus increasing the amount of surface run-off: DeforestationUrbanisationCultivation

72. Human response to Flooding: 1. Flood protection – decreases risk of bankfull capacity being exceeded (Change the channel) 2. Flood abatement – reduces stormflow and reduces peak discharge levels (Change the flow) 3. Behavioural responses – societies adopt different coping strategies ( Deal with the consequences)

73. Human response to Flooding: Flood Protection 1.Dam construction: Controlled release of water stored in reservoir through sluice gates can spread discharge over a longer period (reducing peak flows) Multi-purpose, but key tool for flood protection

76. Human response to Flooding: Flood Protection 2.Flood relief channels: effectively increases bankfull capacity and diverts flow away from high impact zones requires there to be space on floodplains to skirt around high impact zones, so not always possible e.g. River Exe at Exeter, River Thames at Windsor

78. Human response to Flooding: Flood Protection 3. Straightening of sinuous rivers: Allows faster flow rates Thus water levels drop and flood risk is reduced Also reduces deposition and averts bed aggradation Also keeps channels navigable

80. Human response to Flooding: Flood Protection 4.Artificial channel linings: Concrete lined channels create smoother wetted perimeter and so increase velocity Thus water levels drop and flood risk is reduced E.g. Los Angeles

82. Human response to Flooding: Flood Protection 5.Modification to channel or banks: Bank raising and dredging both increase bankfull capacity Bank raising and dredging both increase bankfull capacity By increasing the hydraulic radius, channels also become more efficient (velocity increases and so water levels drop) By increasing the hydraulic radius, channels also become more efficient (velocity increases and so water levels drop) Widely used (e.g. Mississippi – 3000 kms of raised levées – up to 15 m high) Widely used (e.g. Mississippi – 3000 kms of raised levées – up to 15 m high)

87. Human response to Flooding: Flood Protection 6.Spreading grounds: Diverting flood water to low impact flood plain zones, for storage Reduces downstream peak flows Low impact zones can be recreational land use Flood water will evaporate or eventually infiltrate, replenishing groundwater supplies E.g. Los Angeles basin

89. Human response to Flooding: Flood Abatement Tackles problem at source by reducing surface run-off. Achieved by: 7.Afforestation or reforestation of upper catchment slopes (e.g. River Exe) 8. Terracing of farmland 9. Contour ploughing

90. Human response to Flooding: Behavioural responses 10Floodplain zoning Planning authorities can prohibit certain land- uses in the more flood prone floodplain zones 11Flood proofing Individuals bear responsibility for reducing likely flood damage to property Techniques: water-proof garden walls, windows and doors; sandbags; buildings on stilts; removal of damageable goods to higher levels.

91. Human response to Flooding: Behavioural responses 12 Monitoring and Prediction Data on rainfall and stream discharge can be used to produce accurate predictions of the timing of flood surges Data on rainfall and stream discharge can be used to produce accurate predictions of the timing of flood surges

92. Human response to Flooding: Behavioural responses 13Accepting the loss – fatalism often only option in countries like Haiti or Bangladesh 14Public relief funds – emergency response to hazard event requires funding, materials, technical support, rebuilding. Sources vary from UN agencies to governments and NGO’s 15Flood insurance – a standard response in flood prone communities in the North

96. Factors influencing Storm Hydrographs Slope Rock Type Soil Land Use Precipitation / Temp ©Microsoft Word clipart

97. 0 12 24 36 48 30 72 3 2 1 Base flow mm 4 3 2 Rivers with a short lag time and high peak discharge are more likely to flood than rivers with a lengthy lag time and a low peak discharge. WHY? Prediction flooding using a hydrograph

98. Using Storm Hydrographs for flood prediction Rainfall Intensity Rising Limb Recession Limb Lag time Peak flow compared to Base flow Recovery rate, back to Base flow You need to refer to: Basin lag time 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb Recession limb mm 4 3 2 Peak flow

99. ‘Solutions’ to flooding Plant vegetation (increase evapotranspiration - this reduces the amount of water that reaches the river) reduces the likelihood of future flooding reduces the impact of future floods Concrete beds and banks (increase the velocity of the river) Widen and deepen channel (to increase the capacity of the river) Floodplain Zoning Flood relief channels (these increase the capacity of the river by creating more channels) Dams (these control the flow of the water in the upper course and thus reduce flooding. e.g. Donzere on the Rhone) Flood warning systems

100. ‘Solutions’ to flooding How does this solution reduce the likelihood of future flooding?

101. YOU MUST KNOW AT LEAST ONE CASE STUDY OF FLOODING AND DRAINAGE BASIN MANAGEMENT IN LEDCS AND ONE IN MEDCS