2. Hydrograph Record of River Discharge (the level of water flowing down a river channel) over a period of time, they show how certain rivers respond to a rainstorm. River Discharge (the level of water flowing down a river) (is calculated) Storm Hydrographs Show the change in discharge caused by a period of rainfall = cross sectional area rivers mean (average) velocity X (at a particular point in its course)
5. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Base flow Through flow Overland flow Rising limb Recession limb Basin lag time mm 4 3 2 Peak flow Flood Hydrograph
6. The discharge of the river is measured in cumecs - this stands for cubic metres per second 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s)
7. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) mm 4 3 2 Rainfall shown in mm, as a bar graph
8. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) mm 4 3 2 Discharge in m 3 /s, as a line graph
9. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb mm 4 3 2 Rising limb The normal (base) flow of the river starts to rise when run-off, ground and soil water reaches the river.
10. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb mm 4 3 2 Peak flow Peak flow Maximum discharge in the river, the time when the river reaches its highest flow
11. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb Recession limb mm 4 3 2 Peak flow Recession limb shows that water is still reaching the river but in decreasing amounts
12. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Rising limb Recession limb Basin lag time mm 4 3 2 Peak flow Basin lag time The time it takes for the water to find its way to the river
13. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Base flow Rising limb Recession limb Basin lag time mm 4 3 2 Peak flow Base flow Normal discharge of the river
14. 0 12 24 36 48 30 72 Hours from start of rain storm 3 2 1 Discharge (m 3 /s) Base flow Through flow Overland flow Rising limb Recession limb Basin lag time mm 4 3 2 Peak flow Overland flow Through flow + = Storm Flow
15. Volume of water reaching the river from surface run off Overland flow Through flow Volume of water reaching the river through the soil and underlying rock layers