Human and Physical causes of flooding
Flooding occurs when a river’s discharge exceeds its channel’s volume causing the river to overflow onto the area surrounding the channel known as the floodplain. The increase in discharge can be triggered by several events. The most common cause of flooding is prolonged rainfall. If it rains for a long time, the ground will become saturated and the soil will no longer be able to store water leading to increased surface runoff. Rainwater will enter the river much faster. As well as prolonged rainfall, brief periods of heavy rain can also lead to floods. If there’s a sudden “burst” of heavy rain, the rainwater won’t be able to infiltrate fast enough and the water will instead enter the river via surface runoff. This leads to a sudden and large increase in the river’s discharge which can result in a flash flood. Also when snow melts, large volumes of meltwater will enter the river increasing its discharge and triggering floods.
Physical Factors- * The size and shape of a river’s drainage basin dictates how much precipitation the river can receive and how quickly it will arrive (the lag time). A large drainage basin means that the river’s catchment area is large so it will collect a lot of water, increasing discharge. * The permeability of the soil and rock in a drainage basin is a big factor in flooding. If the basin’s soil is impermeable, maybe because it has been saturated by previous rainfall or has been baked by prolonged heating, then any precipitation that falls won’t infiltrate and will instead run straight into the river, increasing the river’s discharge and triggering floods. Similarly, if the rocks in the area are non-porous or impermeable (such as granite or clay) then water won’t be able to infiltrate into the rocks and will, again, run straight off into the river increasing its discharge. * The