A flood occurs when a river bursts its banks and water spills onto the floodplain.
Heavy rain tends to cause flooding. The faster the water reaches the river channel, the more likely it is to flood. The fastest way in which water can reach the river is via surface runoff.
The nature of the landscape will alter the speed at which the water will reach the river. The landscape can be affected by physical and human factors.
Prolonged rainfall: ground will become saturated and impermeable so there will be higher amounts of surface runoff.
Intense rainfall: ground will be unable to infiltrate the high amount of water so there will be higher rates of surface runoff.
Steep-sided channel: faster surface run-off will mean the water reaches the river quickly causing it to overflow.
Lack of vegetation: trees and plants intercept precipitation. If there is little interception then there will be higher surface runoff.
Impermeable rock: water will not be intercepted or percolated so there will be more surface runoff.
Colder temperatures: if the ground is frozen it will become impermeable so there will be higher amounts of surface runoff.
Hard baked ground: ground cannot infiltrate all the rainfall so there will be higher rates of surface runoff.
Snow melt: melting snow can lead to saturated ground and higher rates of surface runoff.
Urbanisation: water will not be intercepted so there will be more surface runoff and it will be faster.
Deforestation: less interception so more surface runoff.