Boscastle Case Study GCSE

On the 16th of August 2004 Boscastle was hit by a flash flood due to extreme rainfall – 200mm of rain fell in 24 hours.

Vishwas Kumar

January 26, 2021

Boscastle Harbour

Location

The town of Boscastle is located in South East England, on the North coast of Cornwall on the Bristol Channel. The town is 43 miles north west of Plymouth and 230 miles east of London, slightly south east.

Geographical Properties

Boscastle is located in a steep sided valley called the Valency Valley, where the river Valency flows down from Marshgate and onto the Boscastle harbour. This has made Boscastle a very pretty sight and subsequently a popular tourist attraction with many National Trust Sites. The land is quite steep, which causes a lot of rainwater to run off the sides into Boscastle once the land becomes saturated. The River catchment is quite small and further up the river, the upland area of Bodmin Moor is relatively impermeable, which causes increased run off. As well as Bodmin Moor, a lot of the rock in this area is impermeable rock like slate and granite and there are also clay soils. The water quite easily runs into the river and increases the risk of flash flooding.

Boscastle is also located just after a confluence of the River Jordan (starting just south of Boscastle) and River Valency, and the valleys of both of these funnel water into the river channel, towards Boscastle.

Before the flood, despite it being August, it had been a very wet summer and had caused the land to become saturated. On the day of the flood there was an unprecedented amount of rainfall, largely due to the remnants of Hurricane Alex, that moved across the Atlantic Ocean and caused extreme rainfall in Cornwall.

Hydrograph

This hydrograph of Boscastle for the day of the flood shows how a lot of rain fell during the earlier hours of the day and then peak discharge as reached around 18:00, which is when the discharge would have risen above the bank full discharge when it peaked around 100 Cumecs. The peak discharge was caused by heavy rainfall earlier that day as well as in the preceding days.

Causes

The heavy rainfall at when the flood occurred was not expected as it was the middle of August, and it was an extremely wet summer. The heavy rainfall was caused by two weather fronts the met over Boscastle, one from over the Atlantic to the west and the other from the east. The most rainfall fell over higher ground above Boscastle, causing all the water to run off into the River. 200mm of rain fell over Ottersham Moor, east of Boscastle, in 4 hours. Furthermore, this convergence of weather, was worsened by the fact that the air mass from the Atlantic was carrying remnants of Hurricane Alex, and it formed large thundery clouds above Boscastle because of the converging winds. In the afternoon the rain fell in unprecedented amounts, estimated at over 1.4 million litres in just 2 hours. in the 24 hours, 200mm of rain and fallen in Boscastle where the average for the whole of August was a mere 75mm. This was probably the greatest cause of the flood. The diagram behind shows how most of the rainfall fell in the upland region behind Boscastle, experience more than 128mm of rainfall.

Brown Willy Effect

The Brown Willy effect was a natural factor contributing to the flood. It is a meteorological phenomenon called peninsular convergence, in the case of Boscastle it is part of Cornwall, which is a peninsula. Heavy showers over Bodmin Moor are caused when moisture laden air from the Atlantic Ocean is slowed by friction and rises over the hills. Brown Willy is the highest point of both Bodmin Moor and Cornwall, being 420m above sea level. In the summer, which is when the flood occurred, the land is heated more than the sea, causing sea breezes during the day. Converging sea breezes from the north and south coasts of Cornwall can lead to very rapid convection over Bodmin Moor. When the flooding happened, it combined with the coastal winds and rising tide, the ground was also already saturated from the rain that had fallen in the last two weeks of above average rainfall. As well as this, the land of Bodmin Moor is relatively impermeable, so this increased surface run off into the rivers.

Physical Causes

There were several other physical causes that contributed to the flood.

The flood happened at high tide.
The soils were quite thin and compiled of impermeable peat soils with become saturated very quickly, so rainfall became surface run off very quickly.
The rock in the local area is slate, which doesn't allow percolation.
The steep sided converging valleys acted as funnels for the water rushing through, funnelling all of the water through to Boscastle.
The Brown Willy Effect
In the days preceding the flood, the whole of the South West of England had experienced stormy weather with heavy rainfall, so the ground was saturated.
On the 16th of August, there was heavy rain, 125mm had fallen in Boscastle alone within a few hours.
The river levels rising due to high amounts of rainfall.
The River Valency had never had a major flood before, so it was unexpected, it was a freak weather event.
There were very few trees in the area to absorb and intercept the rainfall and reduce the amount of surface run off.

Human Causes

As well as physical causes, there were numerous human causes of the flood, which accelerated the floods impacts and increased its likelihood in the first place.
There was no flood control system in the village.
The sewer and drainage system in Boscastle was old and had a very small capacity.
Deforestation on the valley sides and higher ground to make way for agriculture meant there were fewer trees to intercept the rainwater and absorb surface run off.
More buildings in the drainage basin meant more impermeable surfaces, so rainfall and surface runoff flowed into the river much quicker.
Some old bridges got blocked by flood debris, like cars, these acted as dam and eventually when the water smashed through them, there were huge surges of water as high as 5m.

Impacts

Boscastle was completely unprepared for the flood that it was hit by in 2004. Homes and Business were destroyed, and hundreds of vehicles were swept away as bridges and roads were damaged. When the water from the flood did finally recede, tons of mud and debris had been deposited through the lower part of the village and the effect on Boscastle was devastating.

Social Impacts

Water rushed into houses, shops, and pubs and caused damage to a lot of property. As an immediate effect, businesses hat to temporarily shut down and some people had to be evacuated from their homes as it was unsafe to stay there any longer. As a secondary impact, it meant a lot of money was needed for repairs of the homes and business, and this potentially came from the owners if they did not have any insurance. It is also possible that as a result of this insurance prices in this area rose as a direct consequence of the flood and the claims that would have been.
58 properties were flooded, while 4 were completely demolished, including the visitor centre.
Around 1000 residents and visitors are thought to have been directly impacted by the flood, and the rescue mission included rescuing 100 people in 7 helicopters to safety.
Out of 31 Fire brigade stations of Cornwall County, 29 were involved in the rescue operation and remained there for 1 week to help with the clean-up.
4 Footbridges were swept away that were along the Valency Valley.

Boscastle Floods Footage from the BBC

Environmental Impacts

Not only did the floods damage homes and businesses but local wildlife habitats were also destroyed, and small animal will have died.
The cars and debris that flowed out into the sea also caused coastal pollution and it is highly likely that oil from the cars leaked into the ocean.
Riverbanks were eroded by the weight of river water.
Loss of agricultural land, which was very important for many people as there were many landowners.

Debris washed by the River into the bay.

Economic Impacts

There were huge financial costs that uprose from the flood.

The rescue operation that was carried out was very expensive, including the fire service, lifeboats and helicopters.
The clean was also very expensive, for several weeks after the flood.
At least 80 cars were damaged beyond repair as they got swept into the ocean and were later recovered will 32 could still be in the ocean
The destruction and damage of the local area had a significant impact on the local economy as tourism was restricted for quite some time and 90% of the town's income was from tourism. So as a long-term impact people would have seen a reduction in income until Boscastle was again safe for tourists.
The damage that was done to infrastructure could have costed up to £2 million, and the government was the one that had to invest into the repairs, there was also further investment into flood defences of the future.
Due to the flood, there would have been many insurance claims made which will have raised insurance prices. This made it difficult to get insurance in the future for several business and homeowners because it was too expensive.
People will have owned valuable objects, possible family passed down which could have been washed away or damaged by the flood.
Much of the village was washed down by the flood, and there was a cost to find temporary accommodation for the residents.

Management

The flood of 2004 had left Boscastle devastated and it had become apparent that a flood defence was needed for the future. The aim is to reshape and enhance Boscastle's flood defences to create a safe environment for its residents.

The Environment Agency was deeply involved in the management of this flood, and they are responsible for warning people about floods and reducing the likelihood of future floods. The Environment Agency carried out a major project to increase flood defences in Boscastle, so as to prevent a similar flood happening again, or at least reduce the severity of impacts.

The first response was of course the rescue mission, and clean-up. Helicopters were used to rescue the people from trees and rooftops, and the buildings had to be searched. Cars that had been swept away had to be removed from the harbour, although it is believed not all of them could be found. The river channel was cleaned up, where many trees were removed, and the roads were also cleared.

In 2005, an £800,000 flood defence scheme was launched. It included a larger culvert on the river Jordan which as able to carry double the amount of flood water. However, in total £4.5 million has been spent.

In August of 2006, construction started on the River Valency Flood Defence scheme, which is highlighted in the diagram. This was important as the Valency is one of the three rivers that meet in Boscastle. It was in 2008, when construction of the Defence and regeneration was completed, and it is estimated to have cost £10 million.

In certain places along the river flowing through the town, the river has been widened and deepened to increase the capacity, while the bridges have been rebuilt higher and wider so they wouldn't act as dams as they had in 2004.

A new car park has been built that is further back and raised and the existing car park area was raised so that a flood doesn't cause as much damage to cars again, subsequently preventing coastal pollution as well. The car park surfaces were also made of a permeable material so as to reduce run off.

Many trees close to the river channel and dead trees were removed in order to reduce trees that could be swept away and form part of the river debris that could block up bridges and causes them to act as dams. A tree management scheme was also introduced to aid with this. Landowners were also encouraged to maintain vegetation as well as to plant new trees.

Another cause for the impacts of the flood were the poor drainage systems of Boscastle so two new sewage pumps and stations have been put in place to help with the flood flow along the new sewer pipe.

Furthermore, the Deputy Prime Minister and Prince Charles visited the local GP surgery, which acted as the emergency centre, in the days following the disaster. Prince Charles, who is the Duke of Cornwall, made a "substantial" donation to a fund to help rebuild parts of Boscastle, but it is not known how much was donated.

The Environment Agency also introduced a flood warning system for Boscastle. They installed sensors in the river channel to detect changes in the river depth, and if it were to be dangerous it would be able to warn the people of Boscastle. Furthermore, the Environment Agency invested heavily into new ways of predicting heavy rainfall events on a small scale to produce better flood warnings.

Evaluation

The flood management scheme for Boscastle was implemented to help reduce the risk of future flooding, and while it has been quite successful at doing that, it should also be considered whether it was sustainable or not. There was a combination of both hard and soft engineering in terms of the flood defences; the is one of the first steps towards a sustainable management scheme. The inclusion of soft engineering means that they are working with nature, rather than just trying to battle against it, which is what makes it sustainable. Soft engineering, like the tree management scheme was important to help reduce debris that may flow into the river channel and dam the bridges and combined with the widening of the river channel helps reduce the risk of a major flood. as well as the removal of trees, there was also planting of several trees to help keep the soil together and absorb water of trough flow. Hard engineering was also very important. The raising of the car park and use of a permeable surface helped to reduce run off. The other important defence was the improvement of the sewage system, which Boscastle was in dire need of because the one they had was very old and had a very small capacity. However, during the construction of these defences, there was quite a lot of disruption to the residents of Boscastle. The community has also had complaints against the new bridge because it did not fit into the character of the rest of the town. There have also been speculations that these defences would not protect against a flood of this magnitude, but I think it should be enough to reduce the effect of the impacts. Nonetheless, this project has been quite sustainable for the future, due to a combination of hard and soft engineering. It would not have been as sustainable had they just used hard engineering, and not as effective if they just used soft engineering, which is why the combination is very important. It can also be seen that it has been quite effective as there haven't been any major floods since, which could be due to not having as severe weather since then. Overall, I think it has been a successful and sustainable response to the floods.