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Flood Risk Management

Protecting communities and increasing resilience

Exeter and Devon-Wide Floods 4th – 5th October 2021


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Last Updated

Flood Investigation Report

This flood investigation report has been produced by Devon County Council as a Lead Local Flood Authority under Section 19 of the Flood and Water Management Act 2010.

Version Undertaken by Reviewed by Approved by Date
Draft 1 Freya Money Martin Hutchings Martin Hutchings December 2021
Final Freya Money Martin Hutchings  Dave Black January 2021

1. Introduction

The Flood Risk Regulations 2009 and the Flood and Water Management Act 2010 (the Act) have established unitary and upper tier local authorities as the Lead Local Flood Authority (LLFA) for their area. This has placed a number of responsibilities on the LLFA in relation to flood risk management and in particular Section 19 of the Act which states:

Flood and Water Management Act 2010: Section 19 – Local Authorities: investigations

1)     On becoming aware of a flood in its area, a lead local flood authority must, to the extent that it considers it necessary or appropriate, investigate –

a)     which risk management authorities have relevant flood risk management functions, and

b)     whether each of those risk management authorities has exercised, or is proposing to exercise, those functions in response to the flood.

2)     Where an authority carries out an investigation under subsection (1) it must –

a)     publish the results of its investigation, and

b)     notify any relevant risk management authorities.

Flood and Water Management Act (2010), S.19, c.29, London: HMSO

A ‘Risk Management Authority’ (RMA) means:

(a) the Environment Agency (EA),

(b) a lead local flood authority,

(c) a district council for an area for which there is no unitary authority,

(d) an internal drainage board,

(e) a water company, and

(f) a highway authority.

When considering if it is necessary or appropriate to investigate a flood event Devon County Council (DCC) will review the severity of the incident, the number of properties affected and the frequency of such an occurrence. Devon’s Local Flood Risk Management Strategy clearly sets out the criteria to be used when considering a Flood Investigation Report.

Although not all of the locations in this report meet the significance threshold of 5 or more properties flooded, to ensure that the full extent of the flooding is appreciated and recorded it has been decided to include all locations brought to our attention which experienced any internal property flooding, and also other areas of particular concern.

In partnership with the other RMAs in Devon this report has been produced to comply with legislation and to determine the main causes of the flooding. It should be noted that in order to progress with their flood risk management function DCC has opted to develop this report further by considering the various actions that should be considered by the relevant RMA. DCC as the LLFA will continue to monitor the list of actions with all of the RMAs and will assist in the delivery where practical to do so.

Each affected area or group of smaller areas investigated within this report will have a number of recommended actions to be taken forward by the relevant RMAs or in some cases, by the land owner or local community action group. There are various levels of action that can be taken depending on the severity of the situation and the practical solutions available to reduce the risk of further flooding. The recommended actions will generally fall into one of the following categories:

Delivery of Quick win schemes: a solution that can be implemented quickly by the Risk Management Authorities or Local Authority at relatively low cost; some of these have already been completed as this report has been progressed.

Further investigation/research: Further investigations such as catchment studies and hydrological/hydraulic assessments to understand the flow rates and directional paths and evaluate the extent of flooding. These would provide evidence for future capital investment.

Development of Future schemes: Where immediate action is not financially viable or a solution not readily available then a larger scale flood alleviation scheme may be required. In such cases national funding would need to be secured together with additional contributions from others, such as local levy, local authorities and other third parties.

Land owner action: Members of the public who own land adjacent to watercourses have riparian responsibilities and therefore have a duty to maintain their section of watercourse to ensure there is no impediment of flow. Other works to protect their property may also need to be funded by themselves to ensure delivery within their timescales.

Community action: In some cases, it may be prudent for community groups to join forces and deliver and maintain their own local schemes. This may generate further contributions from local levy or the LLFA.

This investigation report will provide a starting point, with suggested actions being further refined in the light of further studies and where possible, through further dialog with the affected communities.

Recommended Actions:

The purpose of this report is to act as a tool for all of the relevant RMAs to understand and appreciate the extent of flooding in their area and to consider and prioritise those actions relevant to their authority. Due to the extent of flooding, not only from the events covered in this report, the level of recommended actions far exceeds the budgets and resources available to enable them to be delivered immediately. Although we take all flooding issues seriously it should therefore be appreciated that some actions may not be progressed within the timescales expected by some residents or communities. Every effort will be made to progress the actions if and when suitable funding is obtained.

The recommended actions highlighted in this report will be used by the LLFA to monitor progress achieved by the RMAs.

2. Risk Management Authority Responsibilities

2.1 Recording Flood Incidents

LLFAs must record flood incidents as part of their duties under the Flood and Water Management Act. The information below shows the national guidance given as part of the Preliminary Flood Risk Assessment Spreadsheet submission to the EA, which outlines information to be collected by LLFAs.

Information the LLFA must record

  • Devon County Council (DCC) will record this on the DCC flood incident database:
  • Start Date
  • Duration of event i.e. days
  • Probability
  • Main source: Surface water runoff; Groundwater; Ordinary watercourses; Artificial infrastructure; Main rivers; The sea; No data
  • Main mechanism: Natural exceedance; Defence exceedance; Failure; Blockage or restriction; or No data
  • Main characteristics: Natural flood; Flash flood; Deep flood; Snow melt flood; No data
  • Significant consequences:
    • To human health (residential properties)
    • To economy (non-residential properties)
    • To the environment (designated sites flooded)

2.2 Key Responsibilities

RMAs in Devon all have their own roles and responsibilities. The general RMA responsibilities in relation to flood risk and surface water management are outlined below:

The Environment Agency is responsible for managing the risk from the sea, Main Rivers and reservoirs and has a strategic overview role for all flood risk management, making it a key local partner for DCC, especially when managing the risk from combined sources and in the event of a large flood incident. The EA also provides a flood warning service throughout England and Wales in areas at risk of flooding from rivers or the sea.

Devon County Council as the Lead Local Flood Authority is responsible for overseeing the flood risk from Ordinary Watercourses, groundwater and surface water runoff. They are also responsible for consenting to works on Ordinary Watercourses and enforcing the removal of any unlawful structure or obstruction within the watercourse. And, as previously stated they must ensure that a flooding investigation is carried out by the relevant authority and publish a report. DCC must also prepare a Local Flood Risk Management Strategy and maintain a register of flood risk assets.

Local District Councils are classified as land drainage authorities with discretionary powers under the Land Drainage Act, such as the implementation and maintenance of flood defences on ordinary watercourses. They also have powers under the Public Health Act to ensure the removal of any blockage within an Ordinary watercourse that is considered a nuisance. As a planning authority they are responsible for the preparation of development plans and making decisions based on planning policy.

Devon County Council as the Highway Authority maintains the highway drainage system to reduce the amount of standing water on the highway. This is achieved by limiting the water on the roads and ensuring that they are kept clear of rainwater; including the maintenance of highway gullies and culverts.

The Highways Agency is responsible for managing, maintaining and improving the Motorway and trunk roads across England and any associated drainage and flood risk.

Land/Property Owners that have a watercourse in or adjacent to their land have riparian responsibilities on that watercourse. This means the landowner must:

  • Let water flow through their land without any obstruction, pollution or diversion which affects the rights of others.
  • Accept flood flows through their land, even if these are caused by inadequate capacity downstream.
  • Keep the banks clear of anything that could cause an obstruction and increase flood risk, either on their land or downstream if it is washed away.
  • Maintain the bed and banks of the watercourse and the trees and shrubs growing on the banks and should also clear any litter or debris from the channel and banks, even if it did not come from their land.
  • Keep any structures, such as culverts, trash screens and debris grills, weirs and mill gates, clear of debris.

The LLFA must also take an overseeing role to ensure that all flood risk is being managed appropriately.

In small localised groundwater and surface water flooding incidents which do not reach the threshold level to trigger a flood investigation by the LLFA under Section 19, the Local Authorities will work in partnership to consider the appropriate action.

All RMAs have a duty to co-operate and to share information in relation to their flood risk management functions.

 

3. Flood Incident Summary and Impact

3.1 Incident Summary

Between the 4th and 5th October 2021, heavy rainfall caused flash flooding to occur across Devon. The worst affected area was Exeter, with other towns and villages such as Blackawton, Dartmouth, and South Huish also experiencing internal property flooding. In total, 25 properties were reported to have experienced internal flooding.

Table 3.1 lists the cities, towns and villages, affected by flooding, and the corresponding number of properties reported to have flooded in each location. These have been identified on figure 3.1 to give spatial context to the distribution and severity of the flood event across Devon. It should be noted that the flooded locations have been reported alphabetically and not in any order of priority. Table 3.2 and 3.3 list the depth of rainfall recorded from the two Environment Agency automatic rainfall gauges that are located closest to the worst affected areas. Table 3.2 shows rainfall data collected from the Exeter Met Office gauge, to capture the rainfall in Exeter, and Table 3.3 shows rainfall data from the Brixham Reservoir gauge, to capture the rainfall near Blackawton and Dartmouth.

Table 3.1 List of cities, towns and villages affected

Location Number of properties flooded Source of flooding
Blackawton 4 Surface Water
Chumleigh 1 Surface Water
Combe Raleigh 1 Surface Water
Dartmouth 3 Surface Water
Dawlish 1 Surface Water
Exeter 9 Surface Water
Honiton 1 Surface Water
Kingskerswell 1 Surface Water
Ottery St Mary 1 Surface Water
South Huish 2 Surface Water
Strete 1 Surface Water

Total properties flooded: 25

 

Map showing the locations of communities flooded during the October 2021 Floods
Figure 3.1: Devon wide map showing locations that were flooded, and the number of properties internally flooded at each location.

 

Table 3.2: Rainfall (mm) recorded at Exeter Met Office on 4th October 2021.

Time Rainfall (mm)
20:45 0.6
21:00 0.8
21:15 1
21:30 2.1
21:45 2.2
22:00 1.9
22:15 1.2
22:30 7.3
22:45 0.6
23:00 0.1

 

Table 3.3: Rainfall (mm) recorded at Brixham Reservoir on 4th October 2021.

Time Rainfall (mm)
20:45 0.9
21:00 1.2
21:15 2.6
21:30 2.1
21:45 2.3
22:00 2.8
22:15 3.6
22:30 10.5
22:45 1.2

 

3.2 Data and Information Collation

It should be noted that this report is only based on the information brought to the attention of DCC through its professional partners, the media, the public and where further investigation by the authorities have identified additional flooded properties. Therefore, it cannot be guaranteed to contain an exact or exhaustive list of individual properties or affected communities in the October 4th – 5th 2021 event.

3.3 Highway Infrastructure

During this event, significant surface water flooding affected the Highway network across Devon. Notable areas affected are detailed in the following list:

  • Flooding of Longbrook Street in Exeter up to knee level
  • Flooding of the A379 in the Strete area
  • Several B roads in Broadclyst, including B3174 and B3181, were unpassable due to fluvial flooding from the River Clyst and the River Cranny
  • Mudslide near Bow Bridge, Ashprington caused the road to be blocked
  • Marjorie Kelly Way Underpass, Ivybridge was flooded due to the River Erme bursting its banks

4. Extent and Impact of Flooding

4.1 Exeter

Heavy rainfall across Devon resulted in high levels of surface run off, which caused drainage systems to become overwhelmed and blocked with debris. Exeter was the area of Devon that recorded the highest number of properties flooded internally as a result of this event, of which, eight were residential and one was commercial. The extent of flooding within Exeter varied, with some properties experiencing ~100mm of internal flooding, and other properties experiencing minor dampness and flooded garages. The road network was also affected by the flood event, with Longbrook Street flooding up to knee level.

4.1.2 Historic Flooding

There has been previous flooding experienced in Exeter. The most notable incidences recorded can be seen in Table 4.1.

Table 4.1 Historic flooding events in Exeter

29/04/2008 4 properties flooded in the Old Tiverton Road area
22/12/2012 9 properties flooded in the Countess Wear area
16/10/2014 12 properties flooded in the St James area
17/08/2020 6 properties flooded in central Exeter

 

4.2 Devon–wide

A number of other areas across Devon were affected by internal property flooding, but with no individual town or village experiencing as many internally flooded properties as Exeter. The affected areas include Blackawton, Chulmleigh, Combe Raleigh, Dartmouth, Dawlish, Honiton, Kingskerswell, Ottery St Mary, South Huish, and Strete. Between these areas, a total of 14 properties were flooded, 13 of which were residential, and one was a doctor’s surgery.

The flooding also caused disruption to highways across Devon. In some areas, roads and walkways were impassable both due to flood water and secondary effects of heavy rainfall, such as mud slides. The intense rainfall and short duration of the localised storm led to a large volume of surface water overwhelming the drainage systems adjacent to the individual properties. Once the peak of the storm passed the drainage systems were able to catch up and continue to drain the area. This confirmed that the event exceeded the capacity of the system and no evidence of blockage.

The following actions in Table 5.1 are recommended for the areas affected in this chapter.

Table 5.1. Recommended actions for the affected areas.

Action By Recommended Action How
General actions recommended for the areas featured in this chapter:
LLFA/ Property Owners Increase community resilience. To install Property Flood Resilience (PFR) measures where necessary in liaison with appropriate Risk Management Authorities. Devon County Council Flood Risk Management (LLFA) currently has a PFR Funding Scheme.
DCC Highways To ensure efficient operation of highway drains and culverts. Review and carry out any maintenance as required.
Parish/Town Council Increase community resilience to affected community. Ensure Community Emergency Plan is up to date. Support available from DCC and Environment Agency.
SWW Ensure efficient operation of public combined and surface water sewers. Continue maintenance regime and consider storm separation where appropriate.
Exeter
DCC Highways To ensure efficient operation of highway drains and culverts. This incident is noted and will be monitored to identify if further action is required in the future.
DCC LLFA / DCC Highways Investigate any opportunities to improve the drainage in the area and reduce the risk of future events. Consider local opportunities to upgrade the drainage systems and/or provide additional gullies, if necessary, in line with other priorities.
DCC LLFA Consider options for mitigating surface water flood risk to areas identified in the Exeter SWMP. Progress further detailed assessment and delivery of identified risks from the Exeter SWMP. Consider preferred options and opportunities for securing funding and resources for potential flood improvement works.
DCC LLFA Increase community resilience on Longbrook Street Deliver the planned Longbrook Street property flood resilience scheme.
Property Owners Consider flood risk to own properties. To install PFR where necessary and make properties more resilient to flooding.
Exeter City Council /

Environment Agency /

DCC LLFA

To ensure flood risk is managed from new developments. Encourage sustainable drainage practices for new developments.
Blackawton
DCC Highways To ensure efficient operation of highway drains and culverts. This incident is noted and will be monitored to identify if further action is required in the future.
Chulmleigh
DCC Highways To ensure efficient operation of highway drains and culverts. This incident is noted and will be monitored to identify if further action is required in the future.
Combe Raleigh
DCC Highways To ensure efficient operation of highway drains and culverts. This incident is noted and will be monitored to identify if further action is required in the future.
Dartmouth
DCC Highways To ensure efficient operation of highway drains and culverts. This incident is noted and will be monitored to identify if further action is required in the future.
Dawlish
DCC LLFA Identified in the local strategy as a high priority community.

 

Continue with flood investigation study and consider local opportunities to reduce risk in line with other priorities

 

DCC LLFA / DCC Highways Investigate any opportunities to improve the drainage in the area. Consider local opportunities to reduce risk in line with other priorities.
Teignbridge District Council Improve drainage of council owned car park. Carry out assessment of existing drainage system and consider options for improving the drainage layout and flow paths.
Honiton
DCC Highways To ensure efficient operation of highway drains and culverts. This incident is noted and will be monitored to identify if further action is required in the future.
Kingskerswell
DCC Highways To ensure efficient operation of highway drains and culverts. This incident is noted and will be monitored to identify if further action is required in the future.
Ottery St Mary
DCC Highways To ensure efficient operation of highway drains and culverts. This incident is noted and will be monitored to identify if further action is required in the future.
South Huish
DCC LLFA / DCC Highways Investigate any opportunities to improve the drainage in the area. Consider local opportunities to reduce risk in line with other priorities.
DCC LLFA / EA Land Management Project Local landowners to be made aware of their responsibilities and informed of better land management practices.

 

Provide advice to local landowners of best land management practices to reduce surface water run-off.
Strete
DCC Highways To ensure efficient operation of highway drains and culverts. This incident is noted and will be monitored to identify if further action is required in the future.

 

6. Next Steps

The next steps following this report will be for DCC as the LLFA to ensure that the recommended action tables in each chapter are presented to the responsible Risk Management Authority. The DCC LLFA will consider their actions in line with other priorities and monitor delivery through regular reviews, whilst working in partnership with DCC Highways, the EA, District Councils, South West Water and the local communities affected.

There is an expectation from DCC of itself and its partners that all authorities involved will cooperate and work together to improve the flood risk in the vulnerable areas identified in this report by completing the recommended actions. As the LLFA, DCC has a responsibility to oversee the delivery of these actions.

Where minor works and quick-win schemes have been identified, these will be prioritised and will be carried out as soon as possible by the relevant authority or landowner, subject to available funding and resources. Any major works requiring capital investment will be considered through the EA’s Medium-Term Plan process.

A review of the actions will be carried out by DCC as the LLFA in order to monitor progress and encourage delivery of recommended actions.