Human management of rivers

• Flooding occurs when a river bursts its banks and overflows onto the surrounding land.
• There are many factors which can cause a flood, often the natural landscape can influence flooding and human interactions can increase the risk.
• Prolonged rainfall can cause flooding as it saturates the land around a river, unable to contain any more liquid.
• Surface run-off is the water that runs over the surface of the land when the soil is unable to absorb it.
• Heavy rainfall can cause flooding as there is less chance of it being soaked up by the soil, so it runs off into the river.
• Lots of vegetation reduces flood risk.
• Deforestation, the cutting down of trees and forests to allow a different land use, will increase the flood risk, as the water will not be intercepted and flow into the river.
• Drains and sewers take water directly to the river which increases flood risk.
• Trees and plants absorb water, a process known as interception.
• The faster the water reaches the river, the more likely it will flood.
• If a valley is made up of impermeable rocks, there is a higher chance of flooding as there is an increase in surface run-off.
• Permeable rocks allow water to pass through its joints and cracks, for example, limestone.
• A steep valley is more likely to flood than a flatter valley because the rainfall will run off into the river more quickly.
• Impermeable rocks do not allow water to pass through them, for example, granite.
• When an area surrounding a river is built on, there is an increase in the amount of tarmac and concrete, which are impermeable surfaces.