Bellwork (back of books)

Bellwork What factors influence flooding? Sort these into physical/human causes Flooding!!! Learning Objectives: Understand the term flood return interval Construct a graph to analyse the flood return

frequency and magnitude for Fema Creek, PA Flood Risk Risk is affected by: The frequency of flooding; how often floods can be expected. The magnitude of the flood; how severe or large each occurrence will be. The number and density of people living in the affected area. The amount of flood protection and prediction systems. The level of economic development; this affects an areas ability to afford

management strategies and preparedness, and its ability to cope in an emergency. Global Flood Risk in the next 30 years Figure 4: Humanitarian risk hotspots for flooding. The map shows flood risk hotspots based on the interaction of extreme and significant flood hazard and high overall human vulnerability. Also shown are areas with significant or extreme flood hazard but lower human vulnerability and areas where climate models predict an increase in extreme precipitation, as an indicator of possible future increases of flood risk.

http://www.careclimatechange.org Flood Risk in the UK Describe the distribution of flood risk in England Magnitude-Frequency Flood Risk Analysis

Floods of a very large size (magnitude) dont happen very often (theyre not very frequent) Floods of a small magnitude are more frequent Large floods usually occur due to unusually heavy or prolonged rainfall There is one exception to this rule! Large floods can still happen in places where there is annual snowmelt or monsoon rains, e.g.

Bangladesh Even in areas where this does not happen it is still possible for very large floods to occur more frequently than expected. By keeping records over many years hydrologists can predict how often a flood of a certain magnitude may occur This is called the flood recurrence interval (RI)

Definition Flood return interval Magnitude-Frequency Flood Risk Analysis A small flood may have a RI of 2 years A huge flood may have a RI of 100 years This information can be used to decide what sort of flood protection is needed and where.

Magnitude-Frequency Flood Risk Analysis TASK Complete the Flood Frequency worksheet for Fema Creek Extension: Make notes from p. 30 about how floods are managed in the UK and how seasonal discharge can be assessed. RECURRENCE INTERVALS

This can allow planners to zone the flood plain and plan land use. They can also be used to predict the occurrence of low flow. In order to minimise the damage from floods it is useful to know how often a flood of a certain size might occur. The time between

flood events of the same size is called the recurrence interval. Work out the discharge for 1. 1.5 years 2.

5 years 3. 20 years Post it Plenary Suggest how flood recurrence could influence land use planning and building

regulations in flood plain areas