GEO002 – Complete River Processes & Flooding
Glossary – Causes, Impacts, Management & Key
Hydrology Terms
When does flooding occur? - When the amount of water exceeds the capacity of the river's channel.
The excess water overflows the river's banks and spills out across the flood plain. It can occur as a
result from persistent rain over a relatively long period of time.
Causes of Flooding (Physical 1) - 1) Weather - Intense rainfall greater than the infiltration capacity of
the ground. Prolonged rainfall leading to the satiation of the ground. Rapid snow melt as
temperatures suddenly rise about freezing.
Causes of Flooding (Physical 2) - 2) Rock - Impermeable rocks limiting percolation and encouraging
rapid surface run off.
Causes of Flooding (Physical 3) - 3) Soil - Low infiltration rate in certain soils (clays)
Causes of Flooding (Physical 4) - 4) Relief - steeps slopes causing fast run off
Causes of Flooding (Physical 5) - 5) Drainage Density - High drainage density means many tributary
systems can carry the rainwater quickly to the main river.
Causes of Flooding (Physical 6) - 6) Vegetation - Low density vegetation absorbs little water and does
not seriously impede run off.
Causes of Flooding (Human 1) - 1) Deforestation - cutting down trees reduces interruption and
speeds up run off.
Causes of Flooding (Human 2) - 2) Urbanisation - concrete and tarmac surfaces together with drains
mean quicker delivery of rain water to the main river.
Causes of Flooding (Human 3) - 3) Agriculture - Risk of flooding increase by leaving soil
bare.
Causes of Flooding (Human 4) - 4) Climate Change - Burning fossil fuels causes melting of ice sheets
and glaciers as well as more rainfall and more frequent storms.
Environmental Impacts of Floods - 1) Landslides
2) Soil contamination by sewage
3) Vegetation destroyed
4) Destruction of settlements
5) Loss of wildlife habitats
6) Soil erosion
Human Impacts of Floods - 1) Loss of belongings
2) Damage to property
, 3) Disease and stress
4) Insurance claims
5) Contamination of water supply and loss of services (gas)
6) Crops and animals lost
7) Death and injury
Primary Effects of Flooding - Loss of life, destruction of property and crops, homelessness, disruption
of transport and communications, loss of water supply and sewage disposal services.
Secondary Effects of Flooding - Cost of replacing what has been lost and damaged, removing the
huge amounts of silt deposited by the floodwaters as they do down.
Controlling Flooding 1 - 1) Construction - Building hard engineering structures such as dams, flood
embankments, sluice gates and spillways. Quite expensive to build.
Problems with Predictions.. - Floods vary. Small floods are meant to occur regularly (every 5 years),
large floods may be expected less frequently (every 50 years?). The question for river managers is to
decide which level of flood they should provide protection, this is called risk assessment. Protecting
against the regular floods is cheap and easy but is it worth investing in the larger infrequent floods?
Managers usually take a middle course and aim to be able to deal with the medium threats of the
large ones. Clearly where the risk is under assessed, protection is likely to prove
inadequate.
Control Flooding 2 - 2) Adjustment/Mitigation - A soft engineering approach to flood control
(restoring a river to its natural state or preserving marshes and wetlands on flood plains to act as
stores of floodwater (like sponges)). Little building on floodplains, flood insurance, warning
systems.
Control Flooding 3 - 3) Prediction - Knowing how high or ride a river can flood helps people decide
where and how things need to be built and dealt with.
Hydrological Cycle - The cycle that shows and describes the movement of water on earth and
includes flows and stores.
Precipitation - When water comes back down to Earth from clouds in the form of hail, rain, snow or
sleet.
Runoff - When water washes off quickly.
Rainfall that does not get absorbed by the soil.
Levee - A embankments on the sides of the river made from layers of sediment deposited from
flooding.
Evapo-transpiration - When water does not return to the sea, but, instead goes back into the
atmosphere, usually by trees and plants.
Groundwater flow - When water flows underground
Confluence - The point where two tributaries meet up together
Glossary – Causes, Impacts, Management & Key
Hydrology Terms
When does flooding occur? - When the amount of water exceeds the capacity of the river's channel.
The excess water overflows the river's banks and spills out across the flood plain. It can occur as a
result from persistent rain over a relatively long period of time.
Causes of Flooding (Physical 1) - 1) Weather - Intense rainfall greater than the infiltration capacity of
the ground. Prolonged rainfall leading to the satiation of the ground. Rapid snow melt as
temperatures suddenly rise about freezing.
Causes of Flooding (Physical 2) - 2) Rock - Impermeable rocks limiting percolation and encouraging
rapid surface run off.
Causes of Flooding (Physical 3) - 3) Soil - Low infiltration rate in certain soils (clays)
Causes of Flooding (Physical 4) - 4) Relief - steeps slopes causing fast run off
Causes of Flooding (Physical 5) - 5) Drainage Density - High drainage density means many tributary
systems can carry the rainwater quickly to the main river.
Causes of Flooding (Physical 6) - 6) Vegetation - Low density vegetation absorbs little water and does
not seriously impede run off.
Causes of Flooding (Human 1) - 1) Deforestation - cutting down trees reduces interruption and
speeds up run off.
Causes of Flooding (Human 2) - 2) Urbanisation - concrete and tarmac surfaces together with drains
mean quicker delivery of rain water to the main river.
Causes of Flooding (Human 3) - 3) Agriculture - Risk of flooding increase by leaving soil
bare.
Causes of Flooding (Human 4) - 4) Climate Change - Burning fossil fuels causes melting of ice sheets
and glaciers as well as more rainfall and more frequent storms.
Environmental Impacts of Floods - 1) Landslides
2) Soil contamination by sewage
3) Vegetation destroyed
4) Destruction of settlements
5) Loss of wildlife habitats
6) Soil erosion
Human Impacts of Floods - 1) Loss of belongings
2) Damage to property
, 3) Disease and stress
4) Insurance claims
5) Contamination of water supply and loss of services (gas)
6) Crops and animals lost
7) Death and injury
Primary Effects of Flooding - Loss of life, destruction of property and crops, homelessness, disruption
of transport and communications, loss of water supply and sewage disposal services.
Secondary Effects of Flooding - Cost of replacing what has been lost and damaged, removing the
huge amounts of silt deposited by the floodwaters as they do down.
Controlling Flooding 1 - 1) Construction - Building hard engineering structures such as dams, flood
embankments, sluice gates and spillways. Quite expensive to build.
Problems with Predictions.. - Floods vary. Small floods are meant to occur regularly (every 5 years),
large floods may be expected less frequently (every 50 years?). The question for river managers is to
decide which level of flood they should provide protection, this is called risk assessment. Protecting
against the regular floods is cheap and easy but is it worth investing in the larger infrequent floods?
Managers usually take a middle course and aim to be able to deal with the medium threats of the
large ones. Clearly where the risk is under assessed, protection is likely to prove
inadequate.
Control Flooding 2 - 2) Adjustment/Mitigation - A soft engineering approach to flood control
(restoring a river to its natural state or preserving marshes and wetlands on flood plains to act as
stores of floodwater (like sponges)). Little building on floodplains, flood insurance, warning
systems.
Control Flooding 3 - 3) Prediction - Knowing how high or ride a river can flood helps people decide
where and how things need to be built and dealt with.
Hydrological Cycle - The cycle that shows and describes the movement of water on earth and
includes flows and stores.
Precipitation - When water comes back down to Earth from clouds in the form of hail, rain, snow or
sleet.
Runoff - When water washes off quickly.
Rainfall that does not get absorbed by the soil.
Levee - A embankments on the sides of the river made from layers of sediment deposited from
flooding.
Evapo-transpiration - When water does not return to the sea, but, instead goes back into the
atmosphere, usually by trees and plants.
Groundwater flow - When water flows underground
Confluence - The point where two tributaries meet up together
