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 it’s ability to cope in an emergency.

Global Flood Risk in the next 30 years Vulnerability means they are vulnerable for natural, human, social, financial or physical reasons, e.g. maybe their livelihood depends on farming so a flood would destroy that, maybe they are are poor so they would be worse affected. They don’t have flood defences or prediction systems. Theres lots of pple living in the area. Figure 4 shows hotspots of flood risk, based on the interaction of high human vulnerability with extreme and significant historic and current flood hazard. In order to better understand how future climate change will affect humanitarian risk, it also shows areas of projected increases in intensity of precipitation, as a proxy of future flood risk. Figure 4 shows that flood risk hotspots occur mainly in the following regions:• • •Africa, including the Sahel, the Horn of Africa, Great Lakes region, Central Africa and Southeast Africa Central, South and Southeast Asia Central America and the western part of South America 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

Describe the distribution of flood risk in England Flood Risk in the UK Describe the distribution of flood risk in England As a starter have a map like the one in the book (or scan one in book) and get Ss to describe pattern of flood risk.

Magnitude-Frequency Flood Risk Analysis 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 Floods of a very large size (magnitude) don’t happen very often (they’re not very frequent) Floods of a small magnitude are more frequent Large floods usually occur due to unusually heavy or prolonged rainfall Even in areas where this does not happen it is still possible for very large floods to occur more frequently than expected. As a starter have a map like the one in the book (or scan one in book) and get Ss to describe pattern of flood risk. 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. As a starter have a map like the one in the book (or scan one in book) and get Ss to describe pattern of flood risk.

Complete the Flood Frequency worksheet for Fema Creek Magnitude-Frequency Flood Risk Analysis TASK Complete the Flood Frequency worksheet for Fema Creek As a starter have a map like the one in the book (or scan one in book) and get Ss to describe pattern of flood risk. Extension: Make notes from p. 30 about how floods are managed in the UK and how seasonal discharge can be assessed.

RECURRENCE INTERVALS 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. 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.

Work out the discharge for… 1.5 years 5 years 20 years

Post it Plenary Suggest how flood recurrence could influence land use planning and building regulations in flood plain areas