Water & Carbon - factors affecting the risk of flooding Flashcards
What is bank full capacity?
The maximum amount of water that a river channel can hold before it overflows its banks. This capacity is influenced by the channel’s shape, size and the surrounding landscape.
What are the five physical factors that increase flood risk?
1) Precipitation
2) Geology
3) Soil Type
4) Relief
5) Drainage basin shapes
How does precipitation increase flood risk?
Intense or prolonged rainfall - can saturate the ground, leading the increased surface run-off.
Heavy, short-duration rainfall - creates a flashy hydrograph due to rapid runoff.
Prolonged, steady rainfall - can lead to a subdued hydrograph as water infiltrates the soil before reaching the river.
How does geology increase flood risk?
Impermeable rocks - prevent infiltration, leading to more surface run-off.
Impermeable surfaces - create a flashy hydrograph due to quick run-off.
Permeable rocks - allow infiltration, leading to a subdued hydrograph.
How does soil type increase flood risk?
Soil permeability affects water absorption
How does relief increase flood risk?
The slope of the land influences the speed at which water flows into rivers.
Steep slopes - cause rapid run-off as it’s easier for water to run over the land than infiltrate the soil.
Gentle slopes - water moves more slowly
How does drainage basin shape increase flood risk?
Affects how quickly water reaches the river.
Circular basins - concentrate water flow quickly.
Elongated basins - spread water flow over a longer period.
What are the four human factors that increase flood risk?
1) Urbanisation
2) Deforestation
3) Agriculture
4) Drainage systems
How does urbanisation increase flood risk?
Development of cities and towns with impermeable surfaces (e.g. concrete and tarmac) increases surface runoff. Building often takes place on the flood plain. Urban areas create a flashy hydrograph due to rapid runoff from impermeable surfaces.
How does deforestation increase flood risk?
Removal of trees reduces interception and increases surface runoff. Trees normally absorb water and slow its movement. Deforested areas create a flashy hydrograph due to increased runoff, whereas forested areas lead to a subdued hydrograph as trees intercept and absorb water.
How does agriculture increase flood risk?
Farming methods, such as ploughing and crop rotation, affect soil structure and water movement. Fields without crops can channel water quickly. Poor agricultural practices create a flashy hydrograph due to increased runoff. Additionally, drainage channels are used to remove excess water from fields, which c
How do drainage systems increase flood risk?
Efficient drainage systems can quickly channel water away from urban areas but may increase flood risk downstream.
Well-maintained drainage systems – can create a flashy hydrograph due to rapid water movement.
Poorly maintained systems – may lead to a subdued hydrograph as water is retained longer
