1. Hydrographs River Discharge = cross sectional area X
A graph which shows the discharge of a river, related to rainfall, over a period of time.
River Discharge
= cross sectional area
rivers mean (average) velocity X
(at a particular point in its course)

2. Rainfall shown in mm, as a bar graph3 2 mm
Discharge (m3/s) 4 1 3 2
Hours from start of rain storm 2

3. Discharge in m3/s, as a line graph2 mm
Discharge (m3/s) 4 1 3 2
Hours from start of rain storm 3

4. Maximum discharge in the river
Peak Discharge
Peak discharge
Maximum discharge in the river 3
Rising limb
Falling limb 2 mm
Discharge (m3/s) 4 1 3 2
Hours from start of rain storm 4

5. Time difference between the peak rainfall and the peak discharge
Lag time
Lag time
Peak discharge
Time difference between the peak rainfall and the peak discharge 3
Rising limb
Falling limb 2 mm
Discharge (m3/s) 4 1 3 2
Hours from start of rain storm 5

6. Use the table below to create your own hydrograph and label the points below
Hours 1 2 3 4 5 6
Time (hrs) 8 10 12 14 16 18 20
Rainfall (mm) 30 40 25 15
Discharge (cumecs) 35 45 80
130
100 70 50
Peak Rainfall The hour of greatest rainfall during a storm
Rising Limb The period of rising river discharge following a period of rainfall.
Peak Discharge The time of maximum discharge by the river
Falling Limb The period of time when the rivers discharge is falling
Lag Time The period of time between peak rainfall and peak discharge

7. Plot the following two discharge graphs
Time (hrs) 2 4 6 8 10 12 14 16 18 20
Discharge 2 (cumecs) 25 30 40 47 50 42 35 27
Discharge 3 (cumecs)
100
140
120 80 65 55 45
Try and give reasons for the different shape of the discharge graphs. Think about the physical and human process at work as well as the rainfall