The hydrograph – a reminder! Key Fact: Shorter Lag Time + Steeper Rising Limb = Increased Flood Risk
Tasks: 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 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.
Natural Factors 1 Weather & Climate Precipitation type (Rain Vs Snow) Length of storm in time ( leading to saturation ) Intensity of rainfall (precipitation exceeds infiltration rate) Seasonality Temperature
Natural Factors 2 Surface Type & Geology Permeability of surface Soil type Rock Type
Natural Factors 3 Vegetation Type (trees, bushes, grasses) Seasonal effects on vegetation (summer vs. winter) Coverage (bare ground Vs Vegetation cover) Interception & storage
Natural Factors 4 Relief (shape of the land) Shape of drainage basin Size of drainage basin Drainage density
Human Factors 1 Urbanization Surface permeability Drainage systems Vegetation removal
Human Factors 2 Agriculture Changes to vegetation Animals Erosion and runoff
Human Factors 3 Changes to the drainage basin River management (dams, flood relief channels) Flood prevention schemes (levees, dredging) Straightening Deforestation
Tasks 2: 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.