Floods (Boscastle) Flashcards
How can precipitation affect the flood risk?
The more precipitation received in a shorter amount of time can increase the chance of flooding as the soil doesn’t have enough time for the water to infiltrate into its layer, creating more surface run off, causing a flood as the lag time decreases. It also doesn’t give the water the chance to percolate deeper into the rock and soil, so there is less through flow and ground water flow.
More precipitation also means that the soil could become fully saturated with water, so further infiltration cannot occur, thus forcing water to flow on the surface rather than in the ground.
How can geology affect the flood risk?
Harder, denser soil or impermeable surfaces can increase surface run off as water is unable to travel to the river channel through the ground reducing the lag time.
How can land use affect the flood risk?
If there are more trees this can decrease the chance of flooding as more interception occurs, giving the soil more time for the water to infiltrate into the soil and percolate into the rock and soil layer increasing the lag time between the water landing on the ground to reaching the channel.
In an urbanised area however, made of concrete and tar, these surfaces don’t allow water to infiltrate through the ground, encouraging surface run off which collects and floods.
How can relief affect the flood risk?
The steeper the relief the more risk in flooding there is, due to gravitational potential energy, the water can be forced straight down into the channel instead of laying on a flat surface, this decreases the lag time as it doesn’t give the water enough time to seep into the ground as its at a high velocity, compared to if it were on a flat surface which the precipitation could seep down into the ground reducing the surface run off and increasing the lag time.
What flood defences did Boscastle develop?
-They strengthened the embankments, which allowed the river to hold a larger capacity of discharge, meaning that the baneful discharge was harder to reach, meaning that flooding wasn’t as likely.
-They changed the bridge, and replaces it with a wider and more open bridge which allows the river and its sediments it may transport in its flow to travel without any disruptions, unlike last time where it was a very low bridge which , when Boscastle flooded, got blocked up with the debris that had fallen due to the flood that created a dam like structure.
-They made the car park raised and prone to flooding, this allowed water to infiltrate into the ground rather than flowing as surface run off to the town.
-They widened and deepened the river channel which increased its bankfull capacity, reducing the chances of the river bursting its banks.
-They installed a gauge to monitor the water levels to predict future floods so the residents can safely evacuate the area in advance, decreasing the rick in life when a flood does occur.
What were some physical reasons why Boscastle needed these flood management schemes put in place? (5)
-Its river has been made narrower over time which reduced its bankfull capacity.
-It’s embankments were old and needed renewing, they could burst when the river reaches its bankfull capacity.
-Its car park was impermeable and the town had lots of urbanised surfaces, which prevented infiltration and percolation.
-Its bridge was too low and was at risk of becoming a dam if it got flooded again and the river’s sediments and load got blocked in it.
-Boscastle was surrounded in steep valley sides which its vegetation was removed previously, which increased the amount of surface run off and decreased the lag time.
What were some social reasons why Boscastle needed these flood management schemes put in place?
Boscastle relies on tourism, 90% of its economy was centred around tourism and after the 2004 flood tourism decreased, so they needed it to encourage tourists to return as they could promise safety.
What hard engineering strategies did Boscastle develop? (3)
-Widened and deepened the river channel
-Built another flood wall and strengthened other embankments.
-Flood relief channels have been created to divert excess water into areas where people aren’‘t at risk.
What soft engineering strategies did Boscastle develop? (3)
-Made the car park permeable
-Placed a gauge to monitor water levels
-Made the old bridge higher and more open.
What are social advantages (2) and disadvantages (3) to Boscastle’s flood management schemes?
Disadvantages-
-People’s lives were disrupted for years to install and renovate Boscastle
-Some argue that the renovated structures ruined the aesthetic and history of the place, deeming it as ugly, lowering their pride they have living there.
-Though the schemes has reduced the flood risk from 1 in 10 yrs to 1 in 75, their still is a risk of another flood occurring, and the extent they need to protect the town would damage the town’s reputation for its beauty.
Advantages-
-The new river and its embankments were made out of local materials to blend in with the town’s look.
-The whole scheme of renewing and restoring the town brought people together, creating more of a community.
What are economic advantages (2) and disadvantages (2) to Boscastle’s flood management schemes?
Disadvantages-
-Turnover in businesses decreased due to the scheme taking place, for example one shop experienced 79% loss of their turnover..
-The scheme cost over £4 million however they could be better, if they were to be more efficient and protect the town fully then it would cost too much.
Advantages-
-More tourists are coming to Boscastle due to the guaranteed safety against a new flood, more precautions such as a gauge have been installed, ensuring their safe stay.
-Housing and businesses are at lower risk of flooding, meaning less businesses are being disrupted and less building are damaged and need reconstructing, allowing the town to focus their money on other investments.
What are environmental advantages (3) and disadvantage to Boscastle’s flood management schemes?
Disadvantages-
-Some may say the bridge doesn’t fit in with the town.
Advantages-
-Biodiversity has increase, with natural habitats and vegetation being maintained.
-Many of the defences look suitable for the town
-Reduced the risk of flooding from 1 per 10 yrs to 1 per 75yrs.
What is soft engineering?
managing a river using natural materials and strategies to mimic a river’s natural processes and adapting life around it.
What is hard engineering?
constructing artificial man-made structures in aim to limit a river’s natural processes and reduce its impact.
What are the 4 hard engineering processes:
-embankments
-channel straightening
-flood relief channels
-dams and reservoirs
