Hydrology - Short Term Variations in Discharge | Back |

Discharge is the flow of  a river as it passes  a particular point along its course. It is usually measured in cubic metres per second (cumecs). There are short-term variations in discharge. Short-term variations are illustrated by a storm hydrograph. Factors such as weather, climate, drainage basin shape and land-use can affect the shape of  a hydrograph. You should be able to annotate a hydrograph and also to interpret other hydrological data.

A Storm Event in  a small drainage basin The table below shows the details from four storm events in  a small drainage basin. It is an unusual question as instead of a storm hydrograph you have  a table of figures to study. (Run-off is the surface discharge of water generated as overland flow.) Storm Event Precipitation Discharge Run-Off   Storm Total (mms) Average Intensity (mm/hour) Max Intensity (mm/hour) Before storm event (cumecs) Peak during storm event (cumecs) As a % of total precipitation A 11.8 3.05 10.16 57 1034 40 B 10.7 2.54 3.56 70 694 31.7 C 30.5 3.05 4.06 9 1019 15 D 16.0 1.52 3.56 79 665 37

1. Which storm had the highest total rainfall?

2. Which two storms had the highest average intensity?

3. Which storm had the highest peak intensity?

4. Which two storms had the highest peak discharges?

5. Which two storms had higher antecedent flows (high flows before this storm?)

6. Which two storms had the greatest increases in discharge?

7. Which two storms had the most run-off?

8. Which two storms probably lasted the longest (over 10 hours each)?

9. Use data from the table to suggest reasons for the relatively high peak discharge for storm event A. (5) Describe the data by quoting relevant figures and then link the figures to an explanation.

10. Use data from the table to suggest reasons for the relatively high peak discharge for storm event C. (5) Describe the data by quoting relevant figures and then link the figures to an explanation.