Clearance and repair to reduce flood risk: local authority guidance

2. Duty to assess each relevant body of water

2.1 What are assessments of bodies of water?

Assessments of bodies of water determine whether the condition of a body of water is likely to give rise to a risk of flooding that is likely to have adverse consequences on receptors ( i.e. will increase flood risk to people, homes, properties or land).

Definitions: 'relevant body of water' (section 17(5))

A 'relevant body of water' means—
- a body of surface water (other than a stretch of coastal water), or
- a body of underground water forming part of a watercourse (but not including a watercourse which is wholly underground);
but does not include sewers and drains which drain into sewers.

A 'body of surface water' has (by virtue of section 55) the same meaning as in section 28(1) of the Water Environment and Water Services (Scotland) Act 2003 ("2003 Act")—
- a discrete and significant element of 'surface water' (such as a loch, a stream, river, canal or other watercourse),
- part of a loch, stream, river, canal or other watercourse,
- a body of 'transitional water', or
- a stretch of 'coastal water'.
(see also sub-definitions for 'surface water', 'transitional water' and 'coastal water' in the 2003 Act, which further define what is meant by a 'body of surface water' in the 2003 Act).

A "watercourse" has (by virtue of section 55) the same meaning as in section 28(1) of the 2003 Act. This expression therefore 'includes all rivers, streams, ditches, drains, cuts, culverts, dykes, sluices and passages through which water flows and includes artificial watercourses and underground watercourses'.

The local authority's assessment of each relevant body of water must be sufficient to ascertain whether or not the condition of that particular body gives rise to a risk of "flooding" of land (whether within or outwith its area).

The term 'flooding' (in section 18(1)) refers to the temporary covering by water from any source of land not normally covered by water, but does not include a flood solely from a sewerage system (see section 3).

Definition: 'flooding' (section 3)

'flooding' means the temporary covering by water from any source of land not normally covered by water, but does not include a flood solely from sewerage system.

"flood risk'' - means the combination of the probability of a flood and of the potential adverse consequences associated with a flood, for human health, the environment, cultural heritage and economic activity.

In the absence of a definition in the Act for 'risk' (as opposed to 'flood risk'). 'risk' in section 18(1) takes its ordinary meaning within the context of the Act.

A local authority must however exercise its functions under Parts 3 and 4 of the Act with a view to reducing 'flood risk' (as defined in section 3). A local authority should therefore carry out assessments under section 18 with a view to reducing overall 'flood risk'.

In ascertaining whether a risk of flooding arises, the local authority should take account of both:

- the probability of a flood, and

- the potential adverse consequences, associated with a flood, for human health, the environment, cultural heritage and economic activity.

Where a relevant body of water in an area gives rise to a 'risk of flooding' and the local authority considers that 'clearance and repair works' would substantially reduce that risk, the local authority must prepare a schedule of those works in accordance with section 18(1)(b).

Definition: 'clearance and repair works' . (section 18(2))

'clearance and repair works' are works that consist of any or all of the following—
- removing obstructions from a body of water,
- removing things that are at significant risk of becoming such obstructions,
- repairing artificial structures which form part of the bed or banks of a body of water.

Where a local authority considers that clearance and repair works would not substantially reduce the risk of flooding (having regard to the combination of the probability of such flooding and the potential adverse consequences), then the local authority is not required to prepare a section 18 schedule.

Chapter 5 (Schedules of Clearance and Repair) provides further guidance.

2.2 Why should assessments be undertaken?

Assessments are required to fulfil the duty on local authorities under section 18 (see Chapter 1) and, along with the schedule of clearance and repair, provide evidence that the general duty of a local authority under section 1 (to exercise its flood risk related functions with a view to reducing overall flood risk) is being discharged.

2.3 Where should assessments be undertaken?

A local authority is required to assess each 'relevant body of water' in its area in accordance with section 18 (see definitions in paragraph 2.1).

It is essential that the nature of flood risk relative to bodies of water is understood before any assessment (or inspection) of 'the relevant bodies of water…for the purpose of ascertaining whether the condition of any such body of water gives rise to a risk of flooding of land' (reference s18(1)(a)).

In some local authority areas the number of relevant bodies of water may be significant. The number and scale of assessments will need to be managed in light of the resources available.

To help ensure that resources for carrying out clearance and repair works are applied in an effective and proportionate way, a risk based approach may be adopted using good practice as encouraged in the Scottish Government's guidance on delivering sustainable flood risk management.

When adopting a risk based approach it is essential to understand the interaction of different actions across catchments. Local authorities may wish to adopt the following approach:

Source

↓

Pathway

↓

Receptor

↓

Impact

This is a well-established framework in flood risk management. It provides a basis for understanding the causal links between the source of flooding, the route by which it is transmitted and the receptor which suffers some impact.

This approach is set out in more detail in the Scottish Government's guidance on delivering sustainable flood risk management.

In essence, a 'risk of flooding' is a combination of two factors:

1. the probability of a flood occurring (in this case, whether the condition of a body of water is likely to give rise to flooding); and

2. the potential adverse consequences of that flooding on receptors.

Although every relevant body of water must be assessed to ascertain whether the condition of the body gives rise to a risk of flooding, each body only requires to be assessed to the extent necessary to ascertain this.

A local authority may wish to carry out an initial screening exercise to assess for each body of water whether, if it were in a poor condition, it would have the potential to give rise to high, moderate, low or a very low risk of flooding (using a risk based approach which takes account of the above factors).

Where any such screening exercise indicates that the body has the potential to give rise to a high or a moderate risk of flooding, then the local authority may wish to prioritise the further assessment of the condition of those particular bodies of water (including by on-site inspection) to ascertain whether the body does in fact give rise to a risk of flooding and, if so, whether it is high, moderate or low.

Any such assessment should be reviewed on a regular basis (with the frequency of any such review being set having regard to the relative flood risk) and updated as appropriate, e.g. as knowledge and experience of the assessment process develops.

Coastal waters

In sections 17 and 18, a 'relevant body of water' means a body of surface water other than a stretch of coastal water.

There is therefore no duty to prepare a section 18 schedule or to carry out works of clearance and repair associated with coastal waters.

However, there may be situations where defences (such as embankments on river estuaries) provide protection from both fluvial and coastal flooding. In such cases, the transitional water will still need to be assessed in accordance with section 18 and, if required, clearance and repair works carried out.

In relation to coastal zones, separate consideration should be given to the Coast Protection Act 1949, under which local authorities (with a coastal zone) have statutory duties and powers to manage coastal erosion.

2.4 When should assessments be undertaken?

Assessments should be undertaken 'from time to time' (section 18(1)).

As indicated in paragraph 2.3, an initial screening assessment of the bodies of water may be undertaken. This should consider all bodies of water even if these are discounted immediately (see paragraph 2.5 for further details).

Once this initial assessment has been done, more specific assessments of individual bodies of water will follow (see paragraph 2.6 for further details).

'Time to time' is not defined in the Act. A local authority may also find it helpful to adopt a risk based approach when deciding the frequency of any re-assessment of a body of water.

2.5 Initial catchment or local authority-wide assessments

Local authorities will be required to use their own local knowledge and judgement to identify the potential flood risk and determine the frequency of assessment of bodies of water. This should consider national guidance for consistency and application of best practice. This consideration should be recorded to allow for review and updating as appropriate, e.g. as knowledge and experience of the assessment process develops.

The initial assessment will be a desk-based exercise. This will utilise a range of existing information, including:

• section 17 Maps of Bodies of Water
• Historical Flood Events/Near Miss Registers
• Previously published Flood Reports under the 1961 Act
• Trash screen Inspection Registers
• National Flood Risk Assessment
• Flood Studies/Post Flood Studies
• SEPA Flood Hazard Maps
• Flood Risk Assessments from all sources e.g. commissioned by the Authority, provided as part of a planning application, etc.

Through the use of geographical information systems and mapping, local authorities are able to identify

• the locations of bodies of water, e.g. watercourses;
• pathways, e.g. topography, roads; and
• receptors; e.g. developments and assets.

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By overlaying knowledge of areas of known risk, based on historical and recorded flood events and also those predicted through modelling and the flood risk management planning process, an initial assessment of prioritisation for more detailed assessment can be made.

The initial assessment of all bodies of water should record what further assessment is required.

The purpose of the further assessments is to determine if any works of clearance and repair would substantially reduce the flood risk.

A simple approach to follow in the first instance is to identify the bodies of water that are considered to present a medium or high risk. Low or no risk bodies of water would be recorded as such and no further assessment planned at this time.

Where bodies of water are classed as at no or low risk, this does not mean that they are no longer to be considered further at all. There should be opportunities to reassess the risk classification based on any future flood events or increasing knowledge.

The medium and higher risk bodies of water (or parts thereof) would then be subject to more detailed desk-based further assessment, and visual inspection may be undertaken.

It is possible that a programme of visual inspections of bodies of water may be used to assist the initial assessment of bodies of water. However, it is more likely that a programme of visual inspections of bodies of water would be required in undertaking further assessments, and in order to inform subsequent reviews of catchment or local authority wide assessments, as deemed appropriate.

The initial catchment or local authority wide assessments should be reviewed on a declared frequency. It is considered that a review every six years to coincide with the Local Flood Risk Management Plan cycle is most appropriate. It may be that for resource issues this is undertaken in year 2 of a cycle.

Other reviews may be appropriate:

• after significant flood events;
• after emergency planning exercises;
• on request; or
• based on new knowledge.

2.6 Further assessments of bodies of water (or parts thereof)

Further assessment of medium or high risk bodies of water (or parts thereof) would involve a more in depth and detailed assessment, so as to establish the priority of the assessment and future frequency for review. The need for a visual inspection should be determined at this time. It should be remembered that the purpose of the further assessments is to determine if any works of clearance and repair would substantially reduce the flood risk. This might be an immediate outcome.

An additional outcome from the assessment would be to determine the requirements for and the frequency of visual inspections and future reassessments.

The assessment may also identify the need for a study into the risks from the body of water, which may include monitoring or modelling. The results of such a study would be used to inform the assessment and future reviews. It is imperative that the outcomes from the assessments, either the initial assessment or further assessments, are managed and recorded. Such records of the assessment process form an invaluable companion to the schedule of clearance and repair.

Assessments can be informed by the evidence collected by inspections. The frequency and extent of inspections are based on the identified needs of the assessments, which are required, planned and managed, and the resources available to undertake them. The risk-based approach allows a targeting of limited resources to locations where visual inspection will offer the greatest benefit, e.g. urban watercourses, trash screens and culverts. In adopting this approach Councils should be aware that at any point there is flexibility in the assessment process to add a stretch of watercourse to the visual inspection programme if additional information becomes available.

Assessments are not inspections

Depending on the skills, knowledge and experience of the inspector (who is the person undertaking the inspection, not necessarily called an inspector), an initial onsite assessment can be made. This initial onsite assessment may lead directly to emergency, urgent or planned works of clearance and repair. However, it is considered that some form of review of such an onsite assessment be undertaken. This should be in the same way that the evidence collected from inspections is subject to assessment.

The frequency of visual inspections of bodies of water to inform the assessments and management of flood risk should also be risk-based, planned and recorded. In this way, inspections form part of the assessment.

For example, categorising the frequency of the inspection programme by risk categories and subsequent reassessments may look like this:

• High Risk – weekly/monthly inspection and reassessment.
• Medium Risk – 6 monthly / yearly inspection and reassessment.
• Low Risk – 2-6 yearly inspection and reassessments.
• Very Low Risk – where no planned inspection frequency may be required, but re-assessments should still be planned.

Based on the assessment of a body of water, there may be particular weather conditions, alerts and warnings that would result in inspections and assessments outside the planned programme at certain locations.

When setting appropriate frequencies of inspections, authorities should take account of technical guidance on inspection of screens/culverts and other flood defence apparatus published by CIRIA or the Environment Agency, as well as maintenance manuals produced for any flood protection schemes or asset management regimes for other assets maintained by the authority. However, it is recognised that many authorities have established their own frequency of assessment based on local knowledge and experience.

Further detailed guidance on visual inspections is included in Chapter 3 of this document.