1. River Drainage Basins & Flooding

3. river evapotranspiration precipitation throughflow surface runoff groundwater flow water table interception percolation infiltration Processes in the Drainage basin system

5. Processes in the Drainage basin system inputs precipitation outputs river runoff evaporation transpiration stores and flows interception surface runoff surface water storage soil water storage groundwater storage infiltration groundwater flow throughflow percolation

6. Rising limb Falling limb Peak discharge Peak rainfall storm flow normal (base) flow Hydrographs I = Lagtime Lagtime = difference between peak discharge and peak rainfall

7. The Flood Hydrograph – Key Words

8. Hydrograph are affected by the characteristics of the drainage basin What affects the shape of a hydrograph? Land use Type and amount of precipitation Geology and soil Gradient of the valley sides Drainage density

9. How do trees reduce flooding? trees intercept the rain evapotranspiration reduces the amount of water that reaches the river water is taken through the roots and so less enters the river

13. Imagine that these two areas have had the same amount of rain over a 24-hour period. Draw a possible hydrograph for each of these areas. A B Hydrographs