Flooding and Flood Prevention

Flooding and Flood Prevention Pgs 72-79

Learning Objective and Learning Outcomes • Learning Objective: To understand the causes, effects and management of river flooding • Learning Outcomes: To know what causes rivers to flood • To understand the effects of river flooding • To understand how the effects of river flooding can be predicted and prevented • To compare the advantages and disadvantages of river defence techniques

When does flooding occur? • Flooding occurs when the level of a river gets so high that it spills over its banks

Waikato River (NZ) after flooding

Physical Factors • Prolonged Rainfall: after lots of rain, the soil becomes saturated so any more rainfall cant infiltrate which increases runoff into rivers. The river then discharges quicker which causes a flood • Relief: how the height of the land changes. Water flows faster on steep slopes so a steep sided valley will allow water to run down into a river faster • Heavy rainfall: increased runoff, which increases discharge • Snowmelt: when snow/ice melts it means alot of water goes into a river in a short space of time • Geology: certain types of rocks (permeable e.g. limestone) absorb water rather than letting it run over the surface but if there is impermeable rocks e.g. clay water flows over the surface faster meaning more runoff and a higher flood risk • Make sure you can identify these factors with the assistance of Fig 23 pg 73

Human Factors • Deforestation: trees stop rainwater hitting the ground directly and they also absorb rain from the ground via their roots. By cutting down trees more water reaches rivers which increases discharge • Building Construction: often made from impermeable materials like concrete and also surrounded by surfaces like tarmac which are also impermeable. These surfaces increase runoff which means the water gets to drains faster and then to rivers faster increasing discharge

Effects of Deforestation/Building Construction

Flood Management

Serious Impacts of Flooding • Floods have many impacts, but the most serious is that people are killed by flood waters, buildings are damaged or destroyed and jobs are lost because of damage to buildings and equipment • The effects of flooding are worse in poorer countries than richer countries because there’s less money to spend on flood protection and to help people after a flood. Also more people live/work in areas that are likely to flood and poorer transport links mean its harder to get help to these places • Think of one rich country that was badly affected by flooding in the last ten years (hint, caused by a hurricane)

Effects of flooding on people and the environment • Using figure 24 pgs 74-75 use each flood listed and in your book write 2/3 bullet points about each flood. See if you can see any similarities from flood to flood

Prediction and Prevention of Flooding • 2.1 million properties a year in UK at risk from flooding, this number keeps increasing • 50% of these are from flooded rivers • Number of ways these effects can be reduced • Met Office predicts flooding and broadcasts this to the public via internet, tv, newspapers etc • Environment Agency also has a website which has a system of warning codes (copy these from Fig 27 on pg 57) • The aim is to reduce the effects of a flood before the flood strikes

Planning and building design • Local Authority has to give permission before a house is built, in flood prone areas this wont be granted unless a flood risk assessment is done • By 2010 all new housing in flood prone areas has to be flood resistant • Different types of measures can be carried out to protect houses depending on the level of risk

Examples of flood protecting your home • Move electrical sockets higher up the wall • Replace doors with lightweight ones that can be easily moved upstairs • Concrete floors instead of wooden floors so they do not rot when wet • Yacht varnish on skirting boards to protect from water • Waterproof timber instead of wood for door frames e.g MDF • Build on stilts

Flooding and Flood Prevention