03 Sec 1 Cht 10 Rivers 08


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03 Sec 1 Cht 10 Rivers 08

  1. 1. Chapter 10 Rivers and Environments
  2. 2. What will I learn today? <ul><li>The Hydrological cycle </li></ul><ul><li>The River System </li></ul><ul><li>The Drainage Basin </li></ul><ul><li>Features formed by Rivers </li></ul><ul><li>Identifying River features on topo maps </li></ul><ul><li>How do rivers affect people? </li></ul>
  3. 3. Distribution of Water on the Earth Salt water (97%) Fresh water (3%) Fresh water Almost three-quarters of the Earth’s surface is covered with water Groundwater (29%) Glaciers, ice sheets (70%) Seas, lakes, rivers (1%)
  4. 4. The Hydrologic Cycle
  5. 5. The Hydrologic Cycle <ul><li>Continuous movement of water from the Earth’s surface into the air, and back onto the Earth </li></ul><ul><li>Water changes state at each stage of the cycle </li></ul><ul><li>Processes occur at the same time </li></ul>Evaporation : Heat from the Sun causes water to change to water vapour Transpiration : Water vapour given out by plants Condensation Rainfall
  6. 6. The Hydrologic Cycle <ul><li>Condensation : Water vapour cools and changes into water droplets </li></ul><ul><li>Rainfall : Water droplets fall as rain or snow </li></ul><ul><li>Rain flows on the Earth’s surface as runoff or seeps into the Earth to be stored as groundwater </li></ul>1 Clouds form when water vapour condenses to form water droplets 2 Water droplets combine to form bigger water droplets 3 Water droplets get bigger and heavier 4 When the water droplets become too heavy to float, they fall as rain or snow
  7. 7. The River System <ul><li>A River is a body of water flowing in a channel. </li></ul><ul><li>The place where a river begins is called a river source. </li></ul><ul><li>Due to gravity a river flows downhill from its source </li></ul><ul><li>The streams and rivers that join a main river are known as its tributaries. </li></ul><ul><li>The river ends when it flows into a lake or sea. This is known as the river mouth. </li></ul>
  8. 8. A river is a body of water that flows in a channel. Aided by gravity, it always flows downhill from its source. A river can be divided into three sections — the upper, middle and lower courses. River source Tributaries River mouth Upper course Middle course Lower course
  9. 9. The Drainage Basin <ul><li>Rivers ‘drain’ the surrounding land by collecting the surface runoff and directing it to the lakes and seas. </li></ul><ul><li>The area that is drained by a river and its tributaries is called the drainage basin. </li></ul><ul><li>Watershed is an imaginary line that separates one drainage basin from another. </li></ul>
  10. 10. The Drainage Basin The area drained by a river and its tributaries River River source Tributary River mouth Drainage basin Watershed
  11. 11. River System
  12. 12. Rivers Features: 1. Valleys <ul><li>Refer to the low area between hills or mountains </li></ul><ul><li>The shape of a valley depends on how the river </li></ul><ul><li>cuts into the land </li></ul>A river cutting through a valley
  13. 13. valley
  14. 14. Rivers Features: 2. Waterfalls <ul><li>A waterfall is formed when a river flows over alternating </li></ul><ul><li>bands of rocks of differing resistance </li></ul><ul><li>As the river flows, the less resistant or softer rock </li></ul><ul><li>is eroded much faster than the more </li></ul><ul><li>resistant or harder rock </li></ul><ul><li>This results in a steep change in gradient </li></ul><ul><li>resulting in a vertical drop of water </li></ul><ul><li>known as a waterfall </li></ul><ul><li>The force of the water is so great that it </li></ul><ul><li>cuts a depression or plunge </li></ul><ul><li>pool at the base of the water fall </li></ul>
  16. 16. Features formed by rivers <ul><li>3. Meanders </li></ul><ul><li>As a river flows over flat land, it forms curves and bends which become more and more noticeable along the river course. </li></ul><ul><li>These bends are called meanders </li></ul><ul><li>Meanders are formed when the river erodes sideways and deposits the sediments it is carrying on the opp side. </li></ul>
  17. 17. Meanders
  18. 18. Meandering System of Rivers
  19. 19. Features formed by rivers TB PG 120 <ul><li>4. Floodplains </li></ul><ul><li>As a river flows through a flat valley, it deposits most of the sediments it is carrying. </li></ul><ul><li>As a result, the bottom of the river bed is raised </li></ul><ul><li>Whenever it rains heavily, the river will overflow its banks and flood the surrounding low-lying land. This land is called a floodplain </li></ul>
  20. 21. Features formed by rivers TB PG 120 <ul><li>5. Deltas </li></ul><ul><li>At the river mouth, the river deposits its sediments into a lake or sea. </li></ul><ul><li>There, the sediments build up slowly and obstruct the flow of the river to the sea. </li></ul><ul><li>When this happens. The river has to flow along alternative channels called distributaries. </li></ul><ul><li>Tributaries join a river but distributaries branch out from a river. </li></ul><ul><li>When layers of sediments have been deposited at the river mouth, a delta is formed. </li></ul>
  21. 22. Diagram of Delta
  22. 23. delta
  23. 24. Delta
  24. 25. How do Rivers Affect People? <ul><li>Positive Impact of Rivers </li></ul><ul><li>Water supply for farming </li></ul><ul><ul><li>Rivers are a important source of water for </li></ul></ul><ul><ul><li>growing crops. </li></ul></ul><ul><li>Fertile soil for farming </li></ul><ul><ul><li>When a river floods its banks, it helps to </li></ul></ul><ul><ul><li>deposit sediments that help increase the </li></ul></ul><ul><ul><li>fertility of the soil </li></ul></ul><ul><ul><li>Farmers plant their crops along the river course </li></ul></ul><ul><li>Source of drinking water and food </li></ul>
  25. 27. How do Rivers Affect People? <ul><li>Production of hydroelectric power </li></ul><ul><ul><li>Rivers are a source of electricity </li></ul></ul><ul><ul><li>A lot of energy is produced when water moves </li></ul></ul><ul><ul><li>quickly in a river </li></ul></ul><ul><ul><li>This energy can be converted into electricity </li></ul></ul><ul><li>Means of transport </li></ul><ul><li>Water supply for industry </li></ul><ul><ul><li>23% of all water drawn by people is used </li></ul></ul><ul><ul><li>in industries </li></ul></ul><ul><li>Recreation and tourism </li></ul><ul><ul><li>Swimming, fishing, sailing, etc… </li></ul></ul>
  26. 29. <ul><li>Negative Impact of Rivers </li></ul><ul><li>Floods can cause the loss of lives and property </li></ul><ul><li>Flooding happens when the water in a river </li></ul><ul><li>overflows its banks </li></ul>How do Rivers Affect People?
  27. 30. Photo 10-3 The satellite image captures a stretch of the Yangtze River and its tributaries. The red portions indicate areas with vegetation. Inset (yellow box) shows the construction site of the Three Gorges Dam.