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)

Rainfall shown in mm, as a bar graph 3 2 mm Discharge (m3/s) 4 1 3 2 0 12 24 36 48 30 72 Hours from start of rain storm 2

Discharge in m3/s, as a line graph 2 mm Discharge (m3/s) 4 1 3 2 0 12 24 36 48 30 72 Hours from start of rain storm 3

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 0 12 24 36 48 30 72 Hours from start of rain storm 4

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 0 12 24 36 48 30 72 Hours from start of rain storm 5

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

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