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Hydrograph

Hydrograph. Interpretation. What is a hydrograph?. a graph to show the relationship between rainfall intensity and stream discharge. Features of a hydrograph. it contains a bar graph showing the amount of rainfall through time ; and a line graph showing the discharge of a stream.

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Hydrograph

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  1. Hydrograph Interpretation

  2. What is a hydrograph? • a graph to show the relationship between rainfall intensity and stream discharge

  3. Features of a hydrograph • it contains a bar graph showing the amount of rainfall through time; • and a line graph showing the discharge of a stream

  4. Features of a hydrograph • after the rain, the discharge of the stream begins to increase. • the rising amount of discharge forms the rising limb.

  5. Features of a hydrograph • after a certain period of time, discharge of the streams comes to the highest, which is called peak discharge.

  6. Features of a hydrograph • when the rain stops, the discharge of the stream will also gradually reduce. • the decreasing amount of discharge forms the falling limb or recession limb.

  7. Features of a hydrograph • the dotted line below is called the base flow • which is the normal discharge of a stream supplied by groundwater.

  8. Features of a hydrograph • the time-lag is the time difference between the rainfall peak and the peak discharge. • the shorter the time lag, the higher the risk of the flood

  9. Factors affecting peak discharge • amount of rainfall • duration of precipitation - longer rainfall --> reduces infiltration, increases overland flow --> high peak discharge • no. of tributaries

  10. Factors affecting time lag • amountof precipitation • duration of precipitation • rate of infiltration • steepness of the slope • human activities, e.g. deforestation

  11. Drainage basin A • more infiltration • more interception • less runoff • smaller peak discharge • smaller amount of discharge • longer time lag • gentle rising limb

  12. Drainage Basin B • less infiltration • no interception by trees • greater surface runoff • higher peak discharge • larger amount of discharge • shorter time lag • steeper rising limb

  13. Drainage Basin C • rain water/surface runoff is trapped in the reservoir • less runoff downstream • water overflows only when the reservoir is full • smaller peak discharge • longer time lag

  14. Which drainage basin has higher risk of flooding? Why?

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