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Annex 3: Example Risk Category Assessment
This chapter to be reviewed by November 2008
HAZARD/THREAT CATEGORY | SUB-CATEGORY: |
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Severe Weather | Flooding: Major Fluvial |
Hazard and Threat Description including Scale: | RISK REFERENCE NO. |
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River Doon, 5 sq. miles (100 homes/8 business premises) and | SW120 sq. miles (500 homes/30 business premises) affected. |
DATE OF REVISION: | NEXT REVIEW DATE: |
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September 2005 | November 2006 |
1. Overview of Hazard or Threat
The catchment of the River Doon is in an upland area and prone to both prolonged rain, intense burst of intense rainfall and heavy snowfall in winter. Three tributaries Merk Water, Doon Burn and Struie Burn influence the potential for flooding as the Doon flows south.
2. Key Evidence
River Doon
1975 The Doon was affected by rapid thawing of snow in the upper reaches of its catchment resulting in flooding below Laxford Bridge and the evacuation of 27 homes in Kirkland. Ten homes were severely damaged.
1996-2004 Flooding of low lying agricultural land has become a frequent event in the Doon Valley. On six occasions sand bags have been prepared and homeowners have made preparations for inundation.
Scotland/ UK
1999 - October/November - two severe rainfall events led to flooding in Glasgow at a scale only expected at a "once in 100 years" likelihood.
2000 - April - Prolonged rainfall in east central Scotland led to 800 homes flooded in Edinburgh. October/November - prolonged severe rainfall led to the flooding of 12,000 homes in UK.
2005 - January - Prolonged heavy rainfall and gales in central and SW Scotland and NW England - the River Eden at Carlisle flooded hundreds of properties with estimated £40 million damage.
This pattern is confirmed in a recent study (Reference) which suggested that patterns of flooding would change over the next 50 years in the UK leading to:
- increased river flows and flood risks in lowland valleys during winter months
- increase in land area covered by 1 in 100 year fluvial indicative floodplain map
- the emergence of a winter flood season with high river flows prolonged periods derived from higher groundwater or run-off
- changes in the pattern of flooding in other seasons
- the frequency and intensity of rainfall appears to be increasing through the effects of climate change.
Likelihood
Hazard and Scale | Likelihood (over 5-year period) and score on Likelihood Scale |
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Major flooding - River Doon, 5 sq. miles affected. | 25% - Score 4 (Possible)* |
Major flooding - River Doon, 20 sq. miles affected. | 2.5% - Score 3 (Unlikely)* |
* Estimated by SCG on basis of national guidance, evidence of previous flooding and evidence of previous flooding and future weather predictions report and flood plain mapping. Occupancy of flood plain areas based on 2001 Census.
Impact
Hazard and Scale | Impact and scores from Impact Scoring Scale |
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Major flooding - River Doon, 5 sq. miles affected. | Health 2, Social 3, Economic 3, Environment, 2. Total Score - 3 (Moderate) |
Major flooding - River Doon, 20 sq. miles affected. | Health 2, Social 5, Economic 4, Environment 3. Total Score - 4 (Significant) |
3. Details of Impact:
Health: Immediate threat of drowning for people, pets and livestock. Possible short-term problem from polluted flood water (sewage, chemicals and fuel stores). Short and longer-term stress-related impact.
Social: Evacuation and temporary/longer-term accommodation and re-housing. Loss of moveable property including vehicles. Damage to buildings and insurance implications. Damage to agricultural land and premises. Public information and advice/support on emergency/ payments benefits. Loss of or damage to utilities and other services - communications, water, gas, electricity - schools. Requirement for community recovery strategy.
Economic: Disruption of road/rail transport, including damage to or loss of bridges in area. Disruption of local business and general disruption of economic life in area, including impact on tourism. Requirement for safety assessments for premises and possible demolition. Relocation/re-building and insurance. Requirement for economic recovery strategy.
Environment: Pollution in flood water and contamination of built and open environment post-flooding. Collection of rubbish/disposal of items post-flooding - link to advice on insurance assessment. Requirement for disinfection and decontamination measures in premises.
4. Vulnerability and resilience
There are a number of areas across Westerland where there is a high potential for flooding based on topography and historical incidents. On the River Doon, these are Kirkland, Haugh of Doon, Merkland and Broomieknowe. In line with the wider picture for the UK, Westerland appears to be experiencing more instances of all forms of flooding in recent times.
Recent forestry harvesting above Kirkland may increase run-off to Struie Burn catchment. Debris washed down from area may reduce flow at Kirkland road bridge. New building at Kirk land riverside area and development of business park at Merkland will require revision of potential houses/business premises affected.
Recent work undertaken by Council below Laxford Bridge has improved flood defences. Additional work planned by Council for creation of flood wall and flood overflow holding area at Kirkland meadow - completion by November 2006.
OVERALL ASSESSMENT
HAZARD / THREAT CATEGORY: | SUB-CATEGORY: |
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Severe Weather | Flooding: Major Fluvial |
Scale | Likelihood | Impact | Risk |
5 sq. miles | Possible | Moderate | High |
20 sq. miles | Unlikely | Significant | Very High |
CONTROLS IN PLACE: Council: Emergency Response Plan; Generic Flooding Plan, "Good Neighbours" Warning Scheme. Other Organisations: Police: Flood alert for Good Neighbours Scheme; Flood Plan for River Doon. Environment Protection Agency: Automated water level and flow system for River Doon and Struie Burn. Early warning arrangements with Police and Council. ADDITIONAL RISK TREATMENT REQUIRED: - Extend Good Neighbours Warning Scheme in preparing self-help arrangements with the local community.
- Work with Kirkland and Haugh of Doon Community Councils to improve local self-help schemes.
- Consider implementing automated telephone warning system for up to 200 premises most at risk.
- Re-assess occupancy/number of households in Kirkland and Merkland areas.
- Review of progress on flood prevention scheme at Kirkland meadow.
- Promote discussion of economic recovery measures through local business forum.
- Major flood exercise 2006 for higher level of flooding.
- Consult with SEPA on likelihood estimates.
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Note: In the above (fictitious) example, two levels of flooding are considered - equivalent to HL20, flash flooding of up to 200 premises and HL19, significant river flooding of 100 to 1,000 premises in the Annex 2 local risk assessment guidance tables.
The lower-scale event is something that has happened in the past and for which plans and flood prevention measures are in place or in development in the SCG area.
The higher level of flooding is estimated to be on the scale of a "one-in-two-hundred-year" event, but for which, in the light of evidence of changing weather patterns both locally and nationally, an SCG may consider that further contingency planning and other measures need to be put in place.
How other more severe river flooding events need to be considered and treated - such as HL18 and H21 in the Annex 2 local risk assessment guidance tables - will depend partly on the local area geography and infrastructure - e.g. the size of urban areas adjacent to rivers - and partly on the need to consider events, which although unlikely could have wide-area or Scottish and UK national impacts.
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