river engineering Flashcards
hard engineering
manmade structure put next to a river to prevent flooding
soft engineering
the use of sustainable or ecological methods to prevent flooding
What do the C,B,A stand for in the CBA structure used for compare river engineering methods
Cost
Benefit
Analysis
- how do dams work?
2. CBA for dams
- Build a wall across a river to control river flow, storing water above the dam in a reservoir to prevent flooding downstream
- very expensive
water in reservoirs can be used as drinking water
reservoirs store water reducing risk of flooding
effective at preventing floods
generate hydroelectric power
But environmental damage, massive impact on local ecosystems and dams could still flood
eroded material is deposited in reservoir and will build up over time reducing carrying capacity
- how do embankments work
2. CBA for embankments
- building walls alongside river banks to prevent flooding when the river levels get too high
2.it is medium cost
stops a lot of flooding
but due to extreme weather because of climate change this may not be enough
impact on wildlife as you are modifying the environment
- how does channel straightening work
2. CBA for channel straightening
- straightening the channel (cutting off the meanders artificially) means more water is moved more quickly away from urban areas so pushing flood water downstream
- isn’t too expensive in comparison to a dam
moves water outer of the area quicker so reduces the risk of flooding
but
moving the problem further downstream
more erosion downstream because the water is flowing faster
- how does a flood relief channel work
2. CBA for flood relief channel
- creating a new channel next to the river to direct water away from urban areas. Can also allow extra river capacity to reduce flooding
- medium cost
takes water away from houses preventing expensive damage to property
but will it be enough climate change more rain more freak weather
more concrete is just increasing surface runoff and reducing infiltration
- how does river restoration work
2. CBA for river restoration
- returning the river to its natural state, where it is allowed to flood in certain areas or creating wetlands to catch/ slow down flood water naturally
- it is very cheap
more infiltration as there won’t be as many impermeable surfaces
better for local ecosystems
less risk of flooding downstream because discharge is reduced
but
the environment may never go back to the way it was again
ruined the soil structure
level of biodiversity may not ever be reached again
- how does flood plain zoning work
2. CBA for flood plain zoning
- more expensive land use is moved further away to reduce damage and costs of flooding
- prevents damage to people’s lives
risk of flooding is reduced
impermeable surfaces aren’t created
impact of flooding is reduced as there is no buildings to damage
but
contradicts warning system as why would you have a warning system if no one lives nearby
expansion of urban areas is limited if there are no other suitable building sites
doesn’t help in areas that are already at risk of flooding and have been built on
doesn’t take the local wildlife in an ecosystem into consideration
- how does a warning system work
2. CBA for warning systems
- warning of floods so people can evacuate through tv, radio, newspapers, internet
- reduces impact of flooding (gives people time to move possessions, place sandbags, evacuate)
prevents death as people can be warned then evacuate
but isn’t doing anything to stop the river flooding and preventing damage to the environment or houses
people may not hear or have access to the warnings
- how does afforestation work
2. CBA for afforestation
- planting trees in the river valley increases interception and lag time so reduces the risk of flash flooding
- not too expensive, no carbon dioxide emissions
flood risk and river discharge are reduced and vegetation reduces soil erosion in the valley and provides habitats for wildlife
but this means there is less land for farming which is a problem with a growing population and trees take a long time to grow