How can flooding be managed? Aim: To understand how humans have increased flooding. To be able to describe and explain different solutions to flooding. Skill: Extractions skills to answer an 8 mark exam question.
Starter: Write out simple definitions of these terms key terms. <ul><li>Peak rainfall </li></ul><ul><li>Peak discharge </li></ul><ul><li>Lag time </li></ul><ul><li>Bankfull level </li></ul>
Human impact. Using the diagram explain how humans have increased the frequency of flooding. Rock Trees River Soil Key words: Deforestation Interception Transpiration Vegetation Roots
Rock Concrete Drains River Human impact. Using the diagram explain how humans have increased the frequency of flooding. Key words: Infiltration permeability surface runoff concrete drains urban
Avoiding flooding. <ul><li>Why would it be a good idea to try and </li></ul><ul><li>lengthen the lag time? </li></ul><ul><li>If humans can manage the time it takes for </li></ul><ul><li>water to reach the river channel, thereby </li></ul><ul><li>increasing the lag time then the river can </li></ul><ul><li>discharge its volume and will be less likely to </li></ul><ul><li>flood. </li></ul>
Flood engineering Two types: Hard and soft engineering, 'Hard' options tend to be more expensive and have a greater impact on the river and the surrounding landscape. 'Soft' options are cheaper, more ecologically sensitive and do not have as large an impact on the river and the surrounding landscape.
Building Dams Dams are often built along the course of a river to control the amount of discharge. Advantages Water is held back by the dam and released in a controlled way. Water is usually stored in a reservoir behind the dam. This water can then be used to generate hydroelectric power or for recreation purposes. Disadvantages Building a dam can be very expensive . Sediment is often trapped behind the wall of the dam, leading to erosion further downstream . Settlements and agricultural land may be lost when the river valley is flooded to form a reservoir.
River engineering Advantages The river channel may be widened or deepened allowing it to carry more water. A river channel may be straightened so that water can travel faste r along the course. The channel course of the river can also be altered, diverting floodwaters away from settlements. Disadvantages Altering the river channel may lead to a greater risk of flooding downstream, as the water is carried there faster.
Afforestation Advantages Trees are planted near to the river. This means greater interception of rainwater and lower river discharge . This is a relatively low cost option, which enhances the environmental quality of the drainage basin. Disadvantages The method is always possible in urbanised areas . Trees do not intercept all of the rainwater so floods can still occur .
Managed flooding (also called ecological flooding) Advantage The river is allowed to flood naturally in places, to prevent flooding in other areas - for example, near settlements. Disadvantage Smaller settlements are still flooded and cannot get house insurance.
Management Advantage Local authorities and the national government introduce policies to control urban development close to or on the floodplain. This reduces the chance of flooding and the risk of damage to property. Disadvantage There can be resistance to development restrictions in areas where there is a shortage of housing. Enforcing planning regulations and controls may be harder in LEDCs .
Describe and explain different solutions to flooding (8 marks). Model answer. Flooding has become a major issue due to human impacts, they have…………… Therefore ………………… This has caused…………... As a result a number of flood engineering techniques have been developed. These can be hard or soft. Both have advantages and disadvantages which are………….. Examples of soft engineering include…………… (explain the ad’s and dis for each). Examples of hard engineering include………… (explain the ad’s and dis for each). Clearly not all techniques are suitable for every river, a number of factors have to be considered before a river is manage, including………………. Key words: Concreted Urbanised Deforested Infiltration Surface runoff Porosity Flooding Settlement Urban Rural Cost Value Population Sustainable.