21. Precipitation Interception Leaf drip etc. Surface Storage Infiltration Soil Storage Percolation Groundwater EvapoTranspiration Overland Flow Channel Storage Throughflow Groundwater Flow River Run Off
22. River DISCHARGE <ul><li>Discharge is the volume rate of water flow, which is transported through the river channel. </li></ul><ul><li>Measured in cumecs (cubic metres per second) </li></ul>
23. DISCHARGE (cumecs) RAINFALL mm time LAG TIME Peak Rainfall Peak Discharge http://www.bbc.co.uk/scotland/education/int/geog/rivers/hydrographs/index.shtml
24. The Flood Hydrograph – A = floods quickly (flash flood) B = slower rate of discharge, less likely to flood WHAT FACTORS AFFECT THE DISCHARGE LINE?
25. So…how can we alter the drainage basin?
26. Urbanisation - homes
27. Urbanisation - Roads
28. Drainage basin – shape and size
29. Geology Which one might be permeable? Which one would slow down the passage of water the most? Which one would be most likely to flood?
30. Deforestation – how would this affect movement of water through the system?
31. Vegetation What processes are shown? How does vegetation affect infiltration? How does vegetation affect the speed of passage of water through the drainage basin? How does vegetation affect the hydrograph shape? A or B?
32. URBANISATION – removing vegetation and increasing RUN OFF
33. Industry Can also discharge water Effect on hydrograph? Effect on water quality? Effect on sediment?
34. TASKS <ul><li>Create a flood hydrograph from the data for River Thaw </li></ul><ul><li>http://www.ngfl-cymru.org.uk/vtc/ngfl/2007-08/geog/hydrology/Flood%20Hydrographs/Activity%203%20-%20Flood%20Hydrograph,%20River%20Thaw.html </li></ul><ul><li>Follow the link above to see what the graph should look like </li></ul><ul><li>Explain the shape of the graph – how is rainfall linked to discharge. </li></ul>
35. Extra Links <ul><li>http://www.geogonline.org.uk/as_drainage.htm </li></ul><ul><li>http://www.ngfl-cymru.org.uk/vtc/ngfl/2007-08/geog/hydrology/front_%20pages/index_floodhydrograph.html </li></ul>