Flooding Flashcards
What is fluvial flooding?
Occurs when excessive rainfall over an extended period of time causes a river to exceed its capacity.
What are the two types of fluvial flooding?
- Overland flooding
- Flash flooding
What is overland flooding?
When water levels exceed the capacity of a river channel
What is flash flooding?
Characterised by an intense, high velocity torrent of water that occurs in an existing river channel with little to no notice.
What is a pluvial flood?
A surface water flood, which is caused when heavy rainfall creates a flood event independent of an overflowing water body
What are two types of pluvial flooding?
- Intense rain saturating an urban drainage system
- Run-off or flowing water from rain falling on hillsides, that are unable to absorb the water.
Name 6 impacts of river floods
- Loss of human life
- Property damage
- Destruction of crops
- Possibility of waterborne diseases
- Loss of land value in a flood plain
- Additional costs of rehabilitation
How is a severity of a river flood determined? (4 ways)
- Amount of precipitation in area (forecasts)
- How long it takes for precipitation to accumulate
- Previous saturation of local soils
- Terrain surrounding the river
What is the recurrence interval?
Refers to the regularity of a flood of a given size
Name 3 ways that an area can prepare people for floods
- Re-zoning of flood plains
- Loss sharing adjustments (e.g. insurance)
- Removal of settlements on floodplains
Name 3 human causes of flooding
- Urban growth (impermeable surfaces)
- Deforestation (more water available = saturated quickly)
- Poor agricultural practices (soil exposure to elements for periods of time - dries up)
Name 3 physical causes of flooding
- Intense rainfall (ground is saturated quickly, also areas cannot deal with large amounts of rainfall in huge amounts)
- Impermeable rock (overland flow = increased river discharge)
- Relief (rapid transfer of water towards rivers = chance of overflow)
Give 3 environmental impacts of flooding
- Deposition of silt
- Meander cut off
- Recharged groundwater stores
Give 3 economic impacts of flooding
- Loss of crops and farm animals
- Overall costs/insurance
- Infrastructure/business damage
Give 2 social impacts of flooding
- Casualties
- Waterborne diseases
What are the two types of engineering which act to prevent or ameliorate flooding?
- Hard engineering
- Soft engineering
What is hard engineering?
Defence schemes that halt a rivers natural processes
What is soft engineering?
Involves the use of the natural environment surrounding a river
What is a dam?
A giant wall built across a rivers channel, to impede its flow.
This helps to control the discharge of the river even during prolonged rainfall
What are the advantages of a dam?
- Used to generate hydroelectric power
- Reservoir can be used for drinking water
What are the disadvantages of a dam?
- Very expensive
- Destroys habitats, as trapped sediment can change the chemical composition of the water
What is straightening (hard)?
Blocking off meanders and constructing alternate, straighter routes.
- This moves water much faster downstream, preventing it from pooling
What are the disadvantages of straightening?
- Flooding is more likely downstream due to increased flow
- Erosion is stronger downstream due to increased kinetic energy
What are artificial levees?
Acts as embankments, extending the channels height and increasing its discharge.
What are the advantages of artificial levees?
- Resistant to erosion due to being constructed out of a strong material
- Allows floodplains to be built on
What are the disadvantages of artificial levees?
- Increase the risk of flooding as urban development on floodplains is risky
- If they do fail flood damage is worse than if the embankments didn’t exist.
What is a diversion spillway?
Artificial channel that a river can flow into when its discharge rises
- Usually have floodgates to control the amount of water in the spillway
What are disadvantages of a diversion spillway?
- Pose a threat to areas near the confluence, increasing the risk of flooding.
- Areas around spillway may not be used to flooding
What is floodplain management?
Involves placing restrictions on land usage in the areas surrounding a river. This limits the amount of construction on the floodplain
Give a disadvantage to floodplain zoning
It is hard to get rid of urban areas that are already in place on the floodplain.
What is wetland and river bank conservation?
Wetland conservation involves creating conditions that are favourable for the development of wetlands (marshes or swamps)
What are the advantages of wetland and river bank conservation?
- Able to store large volumes of water which help to reduce discharge in a river
- Create new habitats for animals, increasing biodiversity
What are the disadvantages to wetland and river bank conservation?
- The reduce the area of land available for farming
What is river restoration?
Involves restoring a river that has undergone hard engineering back to its original course.
- Involves un-straightening a channel, removing artificial levees, and diversion spillways
Give 3 advantages of river restoration
- Reduces the risk of flooding further downstream
- Allows the river to return to its course and reverse any environmental and ecological damage
- No ongoing costs
What are the disadvantages of river restoration?
- Areas needing to be restored may be in use by people
- Land may be valuable, down to government choices
