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Hydrology and Fluvial Geo morphology for CAMBRIDGE AS level

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This power point lesson describes about the hydrology and rivers work in detail with different tools, which is more important for students and candidates of Cambridge Examination at AS level.

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Hydrology and Fluvial Geo morphology for CAMBRIDGE AS level

  1. 1. Hydrology and Fluvial Geomorphology Mr. Yonas Gemeda Addis Ababa 2019
  2. 2. The Drainage Basin System
  3. 3. What does drainage basin mean? • Drainage basin is the area of land drained by a river and its tributaries ( streams ).
  4. 4. Terms definition
  5. 5. Hydrological Cycle
  6. 6. What does it mean? • The hydrological cycle is the system which describe the distribution and movement of water between the earth and its atmosphere. • The model involves the continual circulation of water between oceans, the atmosphere, vegetation and land
  7. 7. Hydrological cycle
  8. 8. Components of drainage basin hydrological cycle Input Flow Store Output Through fall interception Evaporation Stem flow Soil water / soil moisture Precipitation Infiltration Surface water Transpiration Percolation Ground water / base Through flow Channel storage River discharge Base flow Surface runoff
  9. 9. Input • The input is the water that is added to a drainage basin in the form of precipitation. • This can occur in a number of forms, such as a rain, snow and hail. • It can also occur at different times of the year and in different amounts, intensities and frequencies throughout the year.
  10. 10. Outputs • Evaporation is the process by which a liquid is changed in to a gas. • Solid into gas or gas into solid is sublimation • Evaporation is the most important from oceans and seas. • It increases under warm, dry conditions and decreases under cold, calm conditions.
  11. 11. Factors affecting evaporation include: Meteorological factors 1 temperature, 2humidity and 3 wind speed Temperature is most important Other factors 1. amount of water available 2. vegetation cover and 3. albedo
  12. 12. Evapotranspiration • Transpiration is the process by which water vapor escapes from a living plant, principally the leaves, and enters the atmosphere. • The combination effect of evaporation and transpiration are normally referred to as evapotranspiration (EVT)
  13. 13. River discharge • River discharge refers to the movement of water in channel such as stream and rivers. • The water may enter the river as direct channel precipitation or it may reach the channel by surface runoff, groundwater flow, or through flow.
  14. 14. Stores • Interception refers to water that is caught and stored by vegetation. • There are three main components : Interception loss Water that is retained by plant surface s and that is later evaporated away or absorbed by the plant Through fall water that either falls through gaps in the vegetation or that drops from leaves or twigs Stem flow water that trickles along twigs and branches and finally down the main trunk
  15. 15. Cont’d • Soil water ( soil moisture) is the subsurface water in soil and subsurface layers above the water table. From here water may be: • Absorbed • Held • Transmitted downwards towards the water table or • Transmitted upwards towards the soil surface and the atmosphere.
  16. 16. Cont’d • Surface water are a water which stored on the surface. • There are a number of types of surface water. These are :
  17. 17. Temporary Small puddles Seasonal lakes Surface water stores Permanent Lakes Wetlands Swamps Peat bogs Marshes
  18. 18. Cont’d • Ground water refers to subsurface water that is stored under the surface in rocks. • Ground water accounts for 96.5% of all fresh water on earth.
  19. 19. Cont’d • Channel storage refers to all water that is stored in rivers, streams and other drainage channels.
  20. 20. Flows • Through fall refers to water either falls through gaps in vegetation or that drops from leaves or twigs. • Stem flow refers to water that trickles along twigs and branches and finally down the main trunk. • Overland flow is a water that flows over the land’s surface
  21. 21. Cont’d • Overland flow occurs in two main ways: • 1. when precipitation exceeds the infiltration rate • 2. when the soil is saturated
  22. 22. Cont’d • Infiltration is the process by which soaks into or is absorbed by the soil. • The infiltration capacity is the maximum rate at which rain can be absorbed by a soil in a given condition.
  23. 23. Cont’d • Infiltration is inversely related to overland flow and is influenced by a variety of factors, • Duration of rainfall • Antecedent soil moisture • Vegetation cover • Raindrop size and • Slope angle
  24. 24. Cont’d • Water moves slowly down wards from the soil into the bed rock . This is known as percolation • Depending on the permeability of the rock, this may be very slow or in some rocks,
  25. 25. Cont’d • Through flow refers to water flowing through the soil in natural pipes and percolines.
  26. 26. Cont’d • Most groundwater is found within a few hindered meters of the surface but has been found at depths of up to 4 kilometers beneath the surface. • Base flow refers to the part of a river’s discharge that is provided by ground water seeping into the bed of river. • It is a relatively constant flow although it increases slightly following a wet period.
  27. 27. Discharge Relationship within Drainage Basins
  28. 28. Hydrograph • A hydrograph is a line graph showing how water level in a river changes over time. • There are two main types of hydrograph – annual hydrographs (also known as river regimes) and storm hydrographs (also known as flood hydrographs). • Annual hydrographs show variations in the flow of a river over the course of a year, whereas a storm hydrograph shows the variation in the flow of a river for a period of between 1 and 7 days.
  29. 29. Annual Hydrograph
  30. 30. Cont’d • Stream flow occurs as a result of runoff, groundwater springs and input from • lakes and from melt water in mountainous or sub-polar environments.
  31. 31. Cont’d • character or regime of the resulting stream or river is influenced by several variable factors: • l the amount and nature of precipitation • l the local rocks, especially porosity and permeability • l the shape or morphology of the drainage basin, its area and slope • l the amount and type of vegetation cover • l the amount and type of soil cover
  32. 32. Cont’d • Before the storm starts, the main supply of water to the stream is through ground water flow or base flow. • This is the main suppler of water to rivers. During the storm, some water infiltrates into the soil while some flows over the surface as overland flow or runoff. • This reaches the river quickly as quick flow, which causes a rapid rise in the level of the river .
  33. 33. Cont’d • The rising limb shows us how quickly the flood waters begin to rise, whereas the recessional limb is the speed with which the water level in the river declines after the peal. • The peak flow is the maximum discharge of the river as a result of the storm , and • The lag time is the time between the height of the storm and the maximum flow in the river.
  34. 34. Influence on hydrograph • Factors affecting storm hydrographs are: A. precipitation type and intensity B. temperature C. antecedent moisture climate
  35. 35. Cont’d A.Drainage basin size and shape B.Drainage density C. Porosity and impermeability of rocks and soils D.Rock type E. Slope F. Vegetation type G.Land use Drainage basin characteristics
  36. 36. River channel processes and landforms
  37. 37. Channel process Water flows downhill through the river channel. Because the flowing water has Mass and Velocity. It has Energy and it was this energy to do work.
  38. 38. Cont’d • The three works that done in river channel process :  Erosion  Transportation  Deposition Different kinds of land forms
  39. 39. Long profile • Long profile is a line drawn from the source of the river ( where it starts) to the mouth of the river (where it meets the sea). • The typical long profile is concave steeper in the hills and gentler in the lowlands.
  40. 40. Long profile
  41. 41. 1. Erosion • Erosion is the wearing away of the surface of the earth. • Rivers erode their channels as they flow downhill towards the sea.
  42. 42. Why? • Because rivers have • 1. mass and • 2. velocity energy
  43. 43. How ? • The energy of rivers used to erode the rivers channel in four main ways • What are they?
  44. 44. Matching Abrasion Attrition Erosion when particles of sediments bump each other Erosion by direct force of the flowing river water When river can dissolve rocks Erosion by rivers load of sediment. Solution Hydraulic action
  45. 45. Types
  46. 46. Factors • There are a number of factors affecting rates of erosion . These include: 1. Load- the heavier and sharper the load the greater the potential for erosion. 2. Velocity – the greater the velocity the greater the potential for erosion 3. Gradient – increased gradient increases the rate of erosion
  47. 47. Cont’d 4. Geology – soft, unconsolidated rocks such as sand and gravel are easily eroded 5. PH – rates of solution are increased when the water is more acidic 6. Human impact – deforestation, dams and bridges interfere with the natural flow of river and frequently end up increasing the rate of erosion.
  48. 48. Cont’d • Erosion by the river will provide loose material. • This eroded material (plus other weathered material that has moved downslope from the upper valley sides) is carried by the river as its load.
  49. 49. 2. Transportation • How? • Rivers transport the load that is supplied to the in four main ways:
  50. 50. Matching Traction Saltation When the dissolved load transported from soluble rocks Large particles of bed load are rolled along by the force of the flowing water When sand, silt , and clay suspended in the water The small particles of bed load tend to hop along the bed of the river Solution Suspension
  51. 51. Cont’d • The load of a river varies with discharge and velocity. The capacity of a stream refers to the largest amount of debris that a stream can carry, while the competence refers to the diameter of the largest particle that can be carried.
  52. 52. 3. Deposition • Deposition can take place whenever the river loses its energy. Energy Depends on
  53. 53. Causes • There are a number of causes of deposition, such as : A shallowness of gradient, which decrease velocity and energy A decrease in the volume of water in the channel An increase in the friction between water and channel
  54. 54. The Hjulstrom Curve
  55. 55. River Flow
  56. 56. Velocity and discharge • The velocity and energy of a stream are controlled by: The gradient of the channel bed The volume of water within the channel, which is controlled by precipitation in the drainage basin The shape of the channel Channel roughness, including friction
  57. 57. Hjulstrom curves • Hjulstrom curves show what work a river will do (erosion, transport, deposition) • depending on its velocity and the size of material present
  58. 58. Features •There are three important features of Hjulstrom curves: 1. The smallest and largest particles require high velocities to lift them 2. Higher velocities are required for entrainment than for transport 3. When velocity falls below a certain level those particles with a particular settling or fall velocity are deposited.
  59. 59. Patterns of flow • There are three main types of flow: Patters flow/ type Laminar flow Turbulent flow helicoidal
  60. 60. Laminar flow • A smooth, straight channel with a low velocity is required. • This allows water to flow in sheets, or laminae, parallel to the channel bed. • It is rare in reality and most commonly occurs in the lower reaches. • It is more common in ground water and in glacier when one layer of ice moves over another.
  61. 61. Turbulent flow • It occurs where there are higher velocities and complex channel morphology such as a meandering channel with alternating pools and riffles. • Bed roughness also increase turbulence.
  62. 62. Helicoidal flow • A horizontal turbulence often takes the form of helicoidal flow or a corkscrewing motion. • This is associated with the presence of alternating pools and rifles in the channel bed and where the river is carrying large amount of material. • The erosion and deposition by helicoidal flow creates meanders.
  63. 63. Channel type
  64. 64. Types • There are three major types of channel . These are: S •Straight channel M •Meandering B •Braiding
  65. 65. Straight channel • Straight channel are rare . • Even when they do occur the thalweg moves from side to side. • This channel generally have a central ridge of deposited material, due to the water flow patern.
  66. 66. Braiding channel • Braiding channel occurs when the channel is divided by islands or bars. • Islands are vegetated and long-lived, whereas bars are unvegetated, less stable and often short term features .
  67. 67. Factors • Braided channels are formed by various factors: • A steep channel gradient • A large proportion of coarse material • Easily erodible bank material • Highly variable discharge
  68. 68. Cont’d • Braiding tends to occur when a stream does not have the capacity to transport its load in a single channel. • It occurs when river discharge is very variable and banks are easily erodible.
  69. 69. Meanders • Meandering is the normal behavior of fluids and gases in motion. • Meanders can occur on a variety of materials, from ice to solid rock. • The wave length of the meander is dependent upon three main factors • 1. channel width • 2. discharge • 3. nature of the bed and banks
  70. 70. Causes of meanders • There is no simple explanation for the creation for the creation of meanders, and a number of factors are likely to be important.  friction Sand bars Sinuosity Helicoidal flow
  71. 71. Change over time • There are a number of possibilities: • Meanders may migrate downstream and erode river cliffs • They may migrate laterally (sideways) and erode the floodplain • They may become exaggerated and become cut offs (oxbow lakes) • Under special conditions, they may become entrenched or ingrown.
  72. 72. River land forms
  73. 73. POOLS AND RIFFLES • Pools and riffles are formed by turbulence. • Eddies cause the deposition of course sediment (riffles) at high velocity point and fine sediment (pools) at low velocity. • Riffles are small ridges of material deposited where the river velocity is reduced midstream , in between pools (the deep parts of a meander)
  74. 74. Waterfall and gorges • Waterfalls occur where the river spills over a sudden change in gradient, undercutting rocks by hydraulic impact and abrasion, thereby creating waterfall.
  75. 75. Reasons for change • The reasons for this sudden change I gradient along river are: 1. A band of resistant strata 2. A plateau edge 3. A fault scrap 4. A hanging valley 5. Coastal cliffs
  76. 76. Gorges • Gorges are formed by periods of river erosion. • A rapid acceleration in down – cutting is also associated when a river is rejuvenated, again creating a gorge.
  77. 77. Cont’d • Gorges may also be formed as a result of : Antecedent drainage Glacial overflow channeling The collapse of underground caverns in carboniferous limestone area Surface runoff over limestone during a periglacial period The treat of waterfalls Superimposed drainage
  78. 78. Levees and flood plain Levees and flood plain deposits are formed when a river bursts its banks over a long period of time. Deposition of heavy materials which can not move a great distance near a channel edge. This coarse deposits buildup to form embankments called levees.
  79. 79. Cont’d • The finer material is carried further away to be dropped on the floodplain, sometimes creating back swamps. Repeated annual flooding slowly builds up the floodplain. • Old floodplains may be eroded the remnants are known as terraces. • At the edge of the terrace is a line of relatively steep slopes known as river bluffs
  80. 80. Ox- bow lakes • Ox- bow lakes are the result of both erosion and deposition.
  81. 81. Deltas • Deltas are river sediments deposited when a river enters a standing body of water such as a lake, a lagoon, a sea or an ocean. • They are a result of the interaction of fluvial and marine processes.
  82. 82. Cont’d • The material deposited as a delta can be divided into three types. Bottomset beds Foreset beds Topset beds
  83. 83. Cont’d • The character of any delta is influenced by the complex interaction of several variables The rate of river deposition The rate of stabilization by vegetation growth Tidal currents The presence (or absence) of long shore drift Human activity ( deltas often form prime farmland when drained)
  84. 84. Types of delta • There are many types of delta, but the three classic ones are: Arcuate delta Cuspate delta Birds foot delta
  85. 85. Cont’d • Deltas can also be formed inland. When a river enters a lake it will deposit some or all of its load, so forming a lacustrine delta.
  86. 86. The Human Impact
  87. 87. Evaporation and evapotranspiration • There are a number of human impact on evaporation and evapotranspiration. These are:
  88. 88. Dams • There has been an increase in evaporation due to the construction of large dams. • Water loss can be reduced : by using chemical sprays on the water By building sand –fill dams By covering the dams with some form of plastic
  89. 89. Urbanization • It leads to a huge reduction in evapotranspiration due to the lack of vegetation. • There may also be a slight increase in evaporation because of higher temperatures and increased surface storage.
  90. 90. Potential hydrological effect of urbanization Urbanizing influence Potential hydrological response Removal of trees and vegetation Decreased evapotranspiration and interception Increased stream sedimentation Initial construction of housing, streets and culverts Decreased infiltration and lowered ground water table Increased storm flow Decreased base flows during dry periods Complete development of residential commercial and industrial areas Decreased porosity, reducing time of runoff concentration Increase peak discharges and compressing the time distribution of the flow Greatly increased volume of runoff and flood damage potential Construction of storm drains and channel improvement Local relief from flooding; concentration of floodwaters may aggravate flood problems downstream
  91. 91. Interception • Interception is determined by vegetation, density and type. • Most vegetation is not natural but represents some disturbance by human activity.
  92. 92. Impact of Deforestation A decline of surface storage A decline in time lag A reduction in evapotranspiration An increase in surface run of Deforestation
  93. 93. Infiltration and soil water • Human activity has a great impact on infiltration and soil water • Land use changes are important • Urbanization creates an impermeable surface with compacted soil. This reduces infiltration and increases overland runoff and flood peaks.
  94. 94. Advantages of Water storage -Dams • The advantage of dams are numerous, like: • Flood and drought control: • Irrigation • Hydro electric power • Improved navigation • Recreation and tourism
  95. 95. Disadvantages • The disadvantages are : Water losses Salination  ground water change Displacement of population Drowing of archeological sites Seismic stress
  96. 96. Cont’d • Deposition within the lake • Channel erosion • Erosion of delta • Loss of nutrients • Decreased fish catches • Diseases have spread
  97. 97. Flood Risk
  98. 98. Floods • Floods are one of the most common of all environmental hazards. This is because so many people live in fertile river valleys and in low lying costal areas. • The recurrence interval refers to the regularity of flood of a given size. • Small floods may be expected to occur regularly. • Larger floods occur less often but more damaging.
  99. 99. Cont’d • The nature and scale of flooding varies greatly. • Some environments are more at risk than others. The most vulnerable include the following:
  100. 100. Vulnerable environments for flooding Low lying parts of active floodplains and river estuaries Small basins subject to flash floods Areas below unsafe dams Low lying inland shorelines
  101. 101. Causes of flooding • A flood is a high flow of water that overtops the bank of river. • The main causes of floods are climatic forces. • The factors that influence the storm hydrograph determine the response of the basin to the storm. This factors include topography, vegetation, soil type, rock type and characteristics of the drainage basin.
  102. 102. Cont’d • Urbanization increases the magnitude and frequency of floods in at least three ways: 1. Creation of highly impermeable surfaces 2. Smooth surfaces served with dense network of drains, gutters and underground sewers increase drainage density 3. Natural river channels are often constricted by bridge supports or riverside facilities, reducing their carrying capacity
  103. 103. Cont’d • Deforestation is also a cause of increased flood runoff and decrease in channel capacity.
  104. 104. The prevention and amelioration of floods
  105. 105. Forecasting and warning • During the 1980s and 1990s, flood forecasting and warning had become more accurate and these are now among the most widely used measures to reduce the problems caused by flooding. • Despite advances in weather satellites and the use of radar for forecasting.
  106. 106. Cont’d • According to Unites Nations Environment Programme's Publication Early Warning and Assessment, there are a number of things that could be done to improve flood warnings. These include: Improved rainfall and snow pack estimates Better gauging of rivers, collection of meteorological information and mapping of channels
  107. 107. Cont’d Better and current information about human populations and infrastructure Better sharing of information is needed between forecasters, national agencies, relief organizations and the general public.
  108. 108. Loss sharing • Loss-sharing adjustments include disaster aid and insurance. • Disaster aid refers to any aid, such as money, equipment, staff and technical assistance, that is given to a community following a disaster.
  109. 109. Hard engineering • Traditionally, floods have been managed by methods of hard engineering. This largely means dams, levees, wing dykes, and straightened channels that are wider and deeper than the ones they replace.
  110. 110. Hazard – resistant design • Flood proofing includes any adjustment to buildings and their contents that help reduce losses. Some are temporary such as: • Blocking up entrances • Sealing doors and windows • Removal of damageable goods to higher levels • Use of sandbags
  111. 111. Soft engineering • Soft engineering generally refers to working with natural processes and features rather than attempts to control them. They include: • whole catchments • wetland conservation and • river restoration
  112. 112. Cont’d • Physical control of floods depend on two measures 1. Flood abetment : involves decreasing the amount of runoff by reducing the flood peak in a drainage basin. The ways are: • Reforestation • Reseeding of sparsely vegetated areas to increase evaporative loss • Treatment of slopes by contour ploughing or terracing • Comprehensive protection of vegetation from wildfire, overgrazing and clear cutting of forests..etc..
  113. 113. Cont’d 2. Flood diversion : refers to the practice of allowing certain areas, such as wetlands and floodplains, to be flooded to a greater extent.