Boscastle Flood 2004 Case Study Responses To Stress


Floods devastate village

On 16 August 2004, a devastating flood swept through the small Cornish village of Boscastle.

Very heavy rain fell in storms close to the village, causing two rivers to burst their banks. About two billion litres of water then rushed down the valley straight into Boscastle.

Residents had little time to react. Cars were swept out to sea, buildings were badly damaged and people had to act quickly to survive. Fortunately, nobody died – thanks largely to a huge rescue operation involving helicopters — but there was millions of pounds worth of damage.

Physical Impacts

Flooding
On the day of the flood, about 75mm of rain fell in two hours — the same amount that normally falls in the whole of August. Huge amounts of water from this sudden downpour flowed into two rivers, the Valency and Jordan (which flows into the Valency just above Boscastle). Both overflowed, and this caused a sudden rush of water to speed down the Valency — which runs through the middle of Boscastle.

Destruction of houses, businesses and gardens
Floodwater gushed into houses, shops and pubs. Cars, walls and even bridges were washed away. The church was filled with six feet of mud and water. Trees were uprooted and swept into peoples’ gardens. The weight of water eroded river banks, damaged gardens and pavements.

Human Impacts
There was a huge financial cost to the floods. This included:

  • the rescue operation – involving helicopters, lifeboats, and the fire service.
  • the loss of 50 cars
  • damage to homes, businesses and land
  • a loss of tourism, a major source of income for the area

The flooding also had several other key impacts on Boscastle and its inhabitants. These included:

  • environmental damage to local wildlife habitats
  • coastal pollution caused as debris and fuel from cars flowed out to sea.
  • long-term disruption to the village, as a major rebuild project had to be carried out.
  • long-term stress and anxiety to people traumatised by the incident.

Responses to the flooding

  • John Prescott, the Deputy Prime Minister, and Prince Charles visited members of the emergency services and 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 large donation to a fund to help rebuild parts of Boscastle.
  • The Environment Agency is responsible for warning people about floods and reducing the likelihood of future floods. The Environment Agency has carried a major project to increase flood defences in Boscastle, with the aim of preventing a similar flood happening again.
  • We are investing in new ways of predicting heavy rainfall events on a small scale to produce better warnings.

In pictures

Aerial photo of the flood waters gushing through Boscastle (courtesy of Apex News &∓ Pictures)

Slide show of photographs of the Boscastle flood. This link opens in a new window.


Map of the area affected

What happened to cause this event?

Weather map
Fig. 1 shows the weather map for midday on 16 August.

The wind is blowing anticlockwise about the low pressure area, so the air is arriving into Boscastle from a south-westerly direction. It is a warm and moist tropical maritime air mass.

The line labelled (known as a trough line) caused very heavy rain and thunderstorms. A trough is an area of localised rain and thunderstorms. A line of convergence formed near the coast line, where air moving in almost opposite directions collides, this helped to increase the rate of ascent and produced very heavy rain.

There is more about surface pressure charts in the weather section of the Met Office website.

Weather chart

Fig 1. A weather chart from 16/08/2004.

Radar imagery
Fig. 2 shows an animation radar pictures from 12 p.m. (midday) to 7 p.m. on 16 August.

The rainfall rate key shows how the colours in the image relate to the rate the rainfall is falling. For example, the red areas indicate that rain is falling at between eight and 16 mm per hour.

A line of very heavy rain starts at about 1 p.m. on the moors close to Boscastle. It remains over the area for about six hours. Rainfall rates of at least 32 mm per hour are being measured.

There is more about rainfall radar in the weather section of the Met Office website.

Radar imagery

Fig 2. Rainfall Radar

Animation of rainfall radar. Flash Player required.

Satellite imagery
Fig. 3 shows an animation of satellite pictures from 12 p.m. (midday) to 7 p.m. on 16 August

Satellite imagery

Fig. 3: Satellite image

The thickest cloud is shown by the brightest white areas on the picture. The pictures show cloud forming over Boscastle at about 1 p.m. and staying there for much of the afternoon.

Animation of Satellite images(Flash Player required).

Further information on other websites
BBC News website covering the Boscastle flooding
BBC News article – Boscastle one year on

Web page reproduced with the kind permission of the Met Office





Photo source:http://news.bbc.co.uk/1/hi/england/cornwall/3571844.stm

Water stores: There are two rivers which flow into Boscastle and they are the River Jordan and the River Valency.

Date: 16th August 2004

Probability: 1 in 400 but Boscastle is a village which regularly floods, more recently there was one in 2007.

What Happened:

  1. 184mm of rain fell in 24 hours - most of it in a five hour period on 16th August.
  2. Peak intensify of rainfall was over 300mm per hour (which is big!)
  3. An estimated 2 million tonnes of water flowed through Boscastle that day.

CAUSES:

Physical:

  1. Weather + climate- A depression formed in the Atlantic shortly before the flood with the remains of Hurricane Alex which slowed down on the land making the rainfall more immense. The storm was localised (this meant it stayed in one place and surrounding areas received a mere 3mm of water) because there was a trough situated right on top on Boscastle.
  2. Winds - A convergence of the prevailing South-Westerly winds and the path of the depression cause a vertical uplift of air. This lead to the creation of cumulonimbus clouds and more rainfall.
  3. Topography/relief - Boscastle is at the bottom of a steep hill so like a funnel it attracts more overland flow.

Human:

  1. Land use - The upper part of the village has been developing (urbanisation!) Also, hedges have been removed to make fields bigger.
  2. Lack of any flood control system - in the form of either raised banks around the river channel or emergency drainage ditches to catch overflowed water.
  3. The sewer & drainage systems- Boscastle had old sewage systems which had a small capacity. This encouraged surface runoff.



Hydrograph and brute facts...


(Image by Komilla Chadha

  • The lag time of the flood is 4.5-5 hours (This is a short lag time)
  • The peak discharge is 48 cummecs
  • The peak rainfall is 55mm

IMPACTS

Social:

  1. 58 proporties flooded and 4 were swept away by the flood
  2. Fortunately no-one died but there was one injury - a broken thumb!
  3. 32 cars were swept away and never to be seen again
  4. A range of infrastructure was badly damaged
  5. Sewer pipes were blocked and washed away so raw sewage contaminated flood water which caused a severe health risk.
  6. Four footbridges along the Valency were washed away.
  7. Long term disruptions and a major re-building project needed to take place.
  8. Long-term stress and anxiety to people traumatised by the incident.

Economic:

  1. Damage to buildings and services was £2 million.
  2. Rescue operation including helicopters, police, fire service was costly.
  3. Loss of tourism a major source of income to the village of Boscastle.

Environmental:

  1. Damage was caused to local wildlife habitats.
  2. There was costal pollution as debris and fuel from cars flowed out into the sea.

MANAGEMENT

4 Hard engineering defences systems were used; costing £4.6 million

  1. The environmental agency made a decision to lay a large relief culvert that would carry excess rainwater. It is twice the size of the old one.
  2. The River Valency is being widened and lowered from the lower bridge to the car park, so that it has a bigger capacity and can carry more water.
  3. The height of the car park is being raised using stone removed from from the river bed. Also barriers are being made for the car park so that if it floods it takes much longer for the cars to be swept away.
  4. There are plans to demolish the lower bridge near the harbour and replace it with a higher bridge further downstream. This will give the river more capacity and help to reduce flooding.

KEY PLAYER + 3 OF THEIR MAIN FUNCTIONS.

  1. The Environmental Agency : Builds, maintains and inspects flood defence for rivers (including Valency and Jordan).They monitor water levels and flows. They issue warnings, forecasts and implement major incident plans.
  2. The local authority : They deal withs some flooded culverts and roads. Also, they support police in arranging evacuation and providing rest centres. They also arrange emergency accommodation and medical care.
  3. Police: The co-ordinate the emergency response in major floods and helps rescue lives and properties,
  4. Firefighters : Rescue people trapped by floodwater and can pump water our of some buildings.

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