Surpluses within the hydrological cycle Flashcards
What are the meteorological causes of flooding?
Intense storms which lead to flash flooding, as in semi-arid areas but more commonly in mountainous areas.
Prolonged, heavy rain, such as during the Asian monsoon and with the passage of deep depressions across the UK.
Rapid snow melt during a particularly warm spring.
What is flash flooding?
Flash flooding is distinguished but its exceptionally short lag-time. Often minutes or hours.
What are the three major rivers in Bangladesh?
Ganges, Padma and Meghna
What is a storm surge caused by?
A storm surge is caused by very low air pressure which raises the height of the high-tide sea. Strong onshore winds then drive the ‘raised’ sea towards the coast, often breaching coastal defences and flooding large areas.
The likelihood of flooding is increased by what physical circumstances?
In low-lying areas with impervious surfaces, as in towns and cities.
Where the ground surface is underlain by impermeable rocks.
When ice dams suddenly melt and the waters in flacial lakes are released.
Where volcanic activity generates melt water beneath ice sheets that is suddenly released. (Jokulhlaups)
Where earthquakes cause the failure of dams or landslides that block rivers.
What are the human activities increasing the risk of flooding? 12
Grazing animals trample soil.
Ploughing compacts soil.
Streams channelled into culverts to aid rapid drainage of farmland.
Dams built to supply towns with water.
Sprinkling of groundwater on to arable crops.
Wells sunk to supply settlements.
Impermeable areas of tarmac.
Sewers feed water into channel.
Bridge supports built in rivers, ramps on floodplain.
Natural grasslands allow water to sink in, replaced by improved pasture.
Woodlands intercept rain and transpire moisture; roots give good soil structure. Deforestation destroys this.
Natural streams meander and have marshy areas; channelisation does not.
What is channelisation and what is the problem with it?
An effective way of improving river discharge and reducing the flood risk.
The trouble is that it simply displaces that risk downstream. Some other location may well be overwhelmed by the increased discharge.
What is the problem with dams?
Block the flow of sediment down a river so the reservoir gradually fills up with silt; downstream there is increased river bed erosion.
What are river embankments and what is the problem with them?
Designed to protect from floods of a given magnitude. They can fail when a flood exceeds their capacity. Inevitably, when this happens, the scale of the flooding is that much greater.
What are the socioeconomic impacts of flooding?
Death and injury
Spread of water-borne diseases
Trauma
Damage to property, particularly housing.
Disruption of transport and communications.
Interruption of water and energy supplies.
Destruction of crops and loss of livestock
Disturbance of everyday life, including work.
What are the environmental impacts of flooding?
Recharged groundwater stores
Increased connectivity between aquatic habitats
Soil replenishment
For many species, flood events trigger breeding, migration and dispersal.
What is eutrophication?
Eutrophication is the process of nutrient enrichment that ultimately leads to the reduction of oxygen in rivers, lakes and ponds, and the consequent death of fish and other species.
What can the removal of soil and sediment by floodwaters lead to?
Eutrophication of water bodies.
In what years did the UK experience severe floods?
2007
2015-16 winter
What was the basic cause of the severe floods in the UK?
Prolonged rainfall.
