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
amount of 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?