Natural & Human

Key Fact: Shorter Lag Time + Steeper Rising Limb = Increased Flood Risk

 With partner list all of the things that may increase flood risk in a drainage basin / river system…
 Make one list of natural factors that may increase flood risk or cause flooding and another for human factors that may increase flood risk or cause flooding
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Now try to decide what are the most important three factors in each list! – explain why each factor increases flood risk (think about hydrographs and lag time)
Share your answers with the class.

 Weather & Climate
 Precipitation type (Rain Vs Snow)
 Length of storm in time ( leading to saturation )
 Intensity of rainfall (precipitation exceeds infiltration rate)
 Seasonality
 Temperature

 Surface Type & Geology
 Permeability of surface
 Soil type
 Rock Type

 Vegetation
 Type (trees, bushes, grasses)
 Seasonal effects on vegetation (summer vs. winter)
 Coverage (bare ground Vs Vegetation cover)
 Interception & storage

 Relief (shape of the land)
 Shape of drainage basin
 Size of drainage basin
 Drainage density

 Urbanization
 Surface permeability
 Drainage systems
 Vegetation removal

 Agriculture
 Changes to vegetation
 Animals
 Erosion and runoff

 Changes to the drainage basin
 River management (dams, flood relief channels)
 Flood prevention schemes (levees, dredging)
 Straightening
 Deforestation

 Now use your text book (New Wider World)
 Read pages 280 – 281 to reinforce your understanding of these flood risk ideas
 Now read the case study of flooding in Bangladesh p.288-289… make a mind map to represent this flood event – include all of the factors hat led to this flooding… use one color for the natural factors and another color for the human factors.