Delivering sustainable flood risk management: guidance (2019)

Second edition of statutory guidance to SEPA, local authorities and Scottish Water on fulfilling their responsibilities under the Flood Risk Management (Scotland) Act 2009.

5. Selecting and implementing sustainable actions


The main output of the flood risk management planning process should be a set of sustainable actions being taken to reduce overall flood risk across Scotland.

Flood risk management strategies and local flood risk management plans will incorporate a wide spectrum of actions, ranging from national policies to flood protection schemes to awareness raising activities. All options must be identified and considered within a structured appraisal process. This will ensure that options are considered in a consistent way, that alternative options are properly considered and that investment decisions are justified. Sustainable solutions are likely to be a combination of actions.

Where significant investment of public funds is being proposed, actions should be appraised in a manner that is consistent with the guidelines in HM Treasury’s Green Book.

This section provides guidance on:

  • principles to support the selection of sustainable actions;
  • the hierarchy and interaction of different forms of appraisal;
  • the key steps that should be followed in performing an appraisal.

Detailed guidance on the appraisal process is set out separately[9]. The Scottish Government will update existing or issue further guidance on the appraisal process as necessary.

A sustainable approach

In appraising actions for inclusion in flood risk management strategies and local plans, the Act requires that SEPA:

identify actions to achieve objectives in a way which it considers is most sustainable.

Flood management actions that don’t respect the pillars of sustainability- social, economic and environmental, and the need to protect our natural resources for future generations, will not accord with the principles of sustainable development. Guidance on selecting sustainable actions is set out below.

Risk-based decisions

The Act places a duty on SEPA and the responsible authorities to: act with a view to reducing overall flood risk

An understanding of current risk and how that risk might change in space and in time is critical if the most sustainable solution is to be identified. Actions should target those areas where flood risk can be reduced now, while also taking steps to minimise any increase in the existing level of risk in the future. The long-term aim must be to reduce the risk of flooding across Scotland as far as is reasonable, taking full account of environmental, economic and social priorities and needs.

These options should cover the three main ways in which risk can be reduced (Figure 6): avoiding risk, reducing the likelihood of flooding, reducing the impacts of flooding.

Figure 6 Approaches to reducing flood risk

Figure 6 Approaches to reducing flood risk

Decisions on tackling risk should focus on addressing national priorities. However, flexibility must be maintained to allow local priorities to be addressed, particularly where a relatively small amount of investment can address important local priorities and encourage communities to help protect themselves, for example by subsidising flood protection products.

Flooding is a natural process and it is not realistic to expect all flood risk to be eliminated. Areas where it is not feasible to reduce risk or where current risks are believed to be acceptable should be clearly identified. In all cases, risk management actions should include arrangements to deal with residual risks (for example, if design limits are exceeded by floods). This could include promoting actions by individuals, local communities or business to improve property flood resilience and raising awareness of flooding issues and the availability of insurance for any residual risk.

Adopt a long term planning approach

Actions to tackle flood risk should be planned to ensure that any short term actions are part of a coherent longer term plan (50- 100 years) with a view to retaining sufficient flexibility to manage changing risks and societal changes over that period.

Testing flood risk management actions against long term trends will be essential to selecting sustainable actions that will stand the test of time. SEPA and the responsible authorities should work to establish approaches to examining future scenarios that can be applied consistently across flood risk assessments and management decisions. Wherever possible, a range of future scenarios should be examined, including a ‘worst case’ scenario.

The impacts of the changing climate should be consistently taken into account in flood risk management including in appraisals using up to date robust evidence and in accordance with the Scottish Government’s guidance.

Consider a broad and adaptable range of actions

Consideration must be given to a broad range of structural and non-structural options (Figure 7), both individually and in combination across a catchment. In identifying options, careful consideration should be given to:

  • options that prevent sudden catastrophes and enhance recovery;
  • actions that can cope with natural variability and unexpected events;
  • temporary as well as permanent options should be considered, for instance demountable defences;
  • whether abandonment or relocation of property is a better alternative;

Figure 7 Examples of structural and non-structural actions to manage flood risk

Figure 7 Examples of structural and non-structural actions to manage flood risk

SEPA and the responsible authorities should avoid making decisions that will make it more difficult to manage the effects of climate change. This will involve not locking in options that limit further adaptation in the future.

Being flexible may mean that actions are not implemented at a single time. Instead, implementation could be phased and accompanied by monitoring to provide evidence on when or whether further action is needed.

Working with and restoring catchments

As described in Section 2 and 3, all options should be developed in consideration of catchment and coastal processes and characteristics, including consideration of how different interventions interact across a catchment or coastline.

In recognition of the range of potential benefits that can be obtained from working with our natural landscape, all reasonable and practical efforts should be made to enhance the (urban and rural) landscapes natural ability to slow and store flood waters. (Figure 8).

Figure 8 Managing the catchment

Figure 8 Managing the catchment

There is unlikely to be a simple line between natural flood management actions and more traditional engineering, and in many cases options will need to be considered in combination. However, the overriding principle should be to ensure the most sustainable approach is adopted and that all available actions are considered.

As the evidence base for some of these actions is still evolving, wherever possible, monitoring should be undertaken to promote growth of the evidence base. Monitoring will also allow actions to be adapted or refined as evidence on their effectiveness is obtained. Actions which benefit flood risk management to some degree and deliver other benefits, for instance environmental benefits or contributions to climate change adaptation, should be promoted wherever possible.

Moving beyond design standards

Simple consideration of design standards can limit consideration of how factors other than geometry affect the effectiveness of the defence—such as manually operated flood gates, which depend on accurate, timely flood warnings and operational response. More broadly, the design standard, for instance to contain a flood with a 100 year return period (an event that has a 1% probability of occurring in any given year) and which had become a default flood management objective in the past, if adhered to in the future, could limit decisions on how to optimise investment and protect those at greatest risk.

Although there are some benefits to be gained from adopting a common standard of protection for all flood protection work, not least of which is simplicity of communication and simplification of investment planning; this approach would mean that all works would be constructed without due regard to the value or importance of the assets being protected, whether they be people, critical infrastructure, property or the environment.

This guidance does not specify certain design standards. Instead, the approach adopted should be entirely risk based; linking benefits to costs, with the aim of maximising the reduction in overall risk. This approach requires management options to be compared on the basis of the effect that they are expected to have on the frequency and impact of flooding in a specified area. This requires information to predict where flooding will occur (now and in the future) for a range of event probabilities. Estimates of the impacts of this flooding and any mitigation options can then be tested to identify the most cost beneficial option(s).

In practice, it is recognised that design standards are benchmarks. We expect a variety of protection levels to be considered during the design process including 0.5%, 1% and if appropriate a lesser level. As an option we expect actions that protect to a 1% exceedance probability plus allowances for climate change to be included in all appraisals. It is not expected that sewer pipes which are currently built for a 1 in 30 year flood event (3.33%) should be designed to this level. However we would expect SEPA and the responsible authorities to consider the feasibility of designing for protecting to a 1% exceedance through the use of a number of actions including above surface storage etc. Where other design standards are considered, a clear justification must be provided, for instance, where a scheme to protect to a lesser standard is the only technically viable option.

In many cases, particularly when tackling surface water flooding, a combination of actions will need to be brought together (above and below ground) to reduce flood risk. In these cases, the emphasis should be on examining the benefits and costs of combinations of actions against a range of flooding scenarios. For instance, the costs and benefits of upsizing sewers alone compared to the costs of actions to create above ground storage and a small increase in sewer capacity.

An integrated approach to appraisal

Appraisal has an important role to play at all levels of flood risk management, from the preparation of flood risk management strategies and local plans that set out the strategic direction of flood risk management, through to specific projects or schemes (Figure 9).

Figure 9 Roles of appraisal in flood risk management

Figure 9 Roles of appraisal in flood risk management

It is important that appraisal is viewed as part of the process of developing and implementing flood risk management strategies and local plans and the actions set out therein: it should not be viewed or undertaken as a separate process or exercise.

The Act requires close interaction between the preparation of flood risk management strategies and local plans and the implementation of actions. For instance, the power conferred on local authorities to undertake flood protection work, including schemes, can only be exercised where it will contribute to delivering the actions in a flood management plan or not impair delivery of actions set out in plans. Similarly, investment by SEPA in flood warning schemes is expected to be based upon needs identified in flood risk management strategies.

It is therefore important that strategic appraisals underpinning flood risk management strategies and local plans form the outline for appraisals made for the individual projects within the plans. This does not mean that the details of individual schemes will be set out in flood management strategies. Instead, the appraisals will set out catchment focused flood risk management strategies, which should identify the need for particular types of local actions or management response. Where these actions, for instance flood protection schemes or long term land management agreements, require significant public expenditure, more detailed feasibility and appraisal work will be required to ensure that the options and designs reflect local needs.

As discussed in Section 3, the process of preparing flood risk management strategies and local plans should facilitate the process of taking forward and implementing a flood protection scheme. For example, the information generated by SEPA should fulfil, at least in part, early optioneering stages of scheme development, while also supporting subsequent, more detailed assessments and appraisals.

Local scale assessments will need to be consistent with those at a higher level, taking forward the assumptions and principles already agreed on. For example, ensuring that appraisal of shorter-term activity, such as the maintenance of defences, is undertaken in the context of wider strategic objectives as set out in flood risk management strategies.

Throughout the appraisal process:

  • the degree of detail considered should be proportionate to the complexity of the problem and the information required to reach and demonstrate a robust decision;
  • the cost of the appraisal stage should be proportionate to the overall costs and factors associated with delivering the plan, policy or project;
  • the sensitivity of options to changes in cost and benefit assumptions should be tested at different stages of appraisal, to fully understand the uncertainties that exist in the analysis of options.

The appraisal process

All appraisals should go through the following three stages. Additional stages may be added as necessary depending on the purpose of the appraisal and information available.

1. Define the purpose of the appraisal, the issue and the case for intervention and set clear objectives for the appraisal.

2. Describe the impacts (positive and negative) associated with a wide range of possible options. As necessary and appropriate, evaluate impacts in qualitative and quantitative terms and assigning monetary values to them where possible.

3. Compare different options and combinations of options and selecting those that are most appropriate, deliverable and prioritise between actions as necessary.

Guidance on the appraisal process is published separately[9].

Quantifying impacts

To support selection of sustainable actions, SEPA and the responsible authorities will need to ensure that the full ranges of positive and negative impacts of actions are considered in an equitable manner.

Wherever possible, impacts (positive and negative) should be valued in monetary terms. Values should be based on market prices and derived estimates for non-market values where feasible. This is to provide a consistent basis for comparing impacts of different options both at a plan and project level.

Impacts that cannot be valued in monetary terms should always be described, quantified and brought into the appraisal through appraisal summary tables. Understanding these impacts is critical to selecting sustainable actions, and they should not be ignored simply because they are difficult to quantify or value in monetary terms.

The effort invested in valuing impacts should be proportionate to the complexity of the problem and the information required to reach a robust decision. Wherever possible, standard approaches should be used for assessing impacts to ensure consistency within and across different appraisals.


SEPA and the responsible authorities should undertake in-house quality assurance checks of all proposals and post project evaluation, to create a cycle of continuous learning and to understand where policy and delivery can improve. It may also be beneficial for peer reviews to be undertaken to promote best practice and consistency across responsible authorities.

The Scottish Government may review a sample of appraisals after they have been approved. This will help determine how the principles in this guidance are being applied and whether further guidance is necessary.

Implementing actions

Consideration of sustainability does not end when the best actions have been selected. It is also important that actions are implemented in a sustainable manner. It is not the purpose of this guidance to set out how this can best be achieved, but the following principles should be applied.

  • aim to minimise construction waste;
  • maximise the reuse of materials;
  • adopt low carbon construction strategies;
  • ensure designs support the principle of adaptive management wherever possible.
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