Flood protection schemes - assessment of economic, environmental and social impacts: guidance

4. DESCRIBE: Identifying and short-listing a range of actions

Identifying and short-listing a range of actions

Importance of a good choice of options

4.1 Cost-benefit analysis can only identify the best of those options considered. A good appraisal will, therefore, encompass a wide range of management options, if only to rule out many of these at an early stage. A narrowly defined search may only identify the best of a poor set.

4.2 Options may reduce the likelihood of an event, or reduce the damages when an event occurs. Institutional or behavioural adaptations, such as relocation of some activities, or the temporary closure of roads when flood warnings are in force, may be considered in addition to the construction of works.

4.3 The form of the detailed analysis also depends on the situation and physical aspects of the land, whether or not there is an existing scheme, and whether there are any statutory or other legal constraints affecting the choice of options. The residual life and standard of protection offered by any existing scheme should also be taken into account. These different conditions determine the appropriate 'do nothing' and 'do something' options.

Identifying the 'do nothing' option

4.4 Benefits and costs for all 'do something' options should be compared with those of the 'do nothing' case. The latter provides a convenient common baseline against which the other options can be assessed. Scheme benefits are calculated from the losses avoided by carrying out the proposed works rather than doing nothing.

4.5 Identifying the 'do nothing' option correctly is therefore important to the analysis and needs careful consideration. Where there is no existing scheme, the 'do nothing' option is obvious; there is no intervention in natural processes.

4.6 Where there is an existing scheme, the 'do nothing' option will be to walk away and abandon all associated maintenance and repair, allowing nature to take its course. Simply continuing with maintenance and repair of the existing structure then becomes one of the 'do something' options.

4.7 While it might appear impossible for political or other reasons to abandon the area, this should mean that the advantages of preserving what is there are overwhelming. It should therefore be easy to demonstrate that continuing present practice is better than the 'do nothing' option. If this is not the case, the non-economic reasons for continuing must be carefully considered. For health and safety reasons, it may be necessary to take minimal steps to make any abandoned works safe and these costs should be taken into account.

4.8 In some cases, due to the statutory duty to carry out clearance and repair works to bodies of water ( Flood Risk Management (Scotland) Act 2009, section 59), it may be necessary to use the 'do minimum' option as the baseline. Otherwise, this option will only be appropriate when there is interdependence between action on the site and other areas, such that the cost of analysing the 'do nothing' case is disproportionate compared to the size of the project.

4.9 The 'do nothing' options should be:

• where there is an existing scheme, walk away: cease all maintenance, repairs and similar activities immediately;
• where there is an existing scheme, and walking away is not permissible for legal or statutory reasons, adopt the 'do minimum' option;
• where there is no existing scheme, do nothing; do not intervene in natural processes.

Identifying the 'do something' options

4.10 In the early stages of analysis, the range of options should be as wide as possible; the process of analysis may itself suggest new options. This guidance does not specify certain design standards. Instead, the approach adopted should be risk-based, linking benefits to costs with the aim of maximising the reduction in overall risk. As described in chapter 5 of 'Delivering Sustainable Flood Risk Management' (reference 1), we expect a variety of protection levels to be included during option development including 0.5%, 1% and if appropriate a lesser level. As an option, we expect actions that protect to a 1% AEP plus allowances for climate change to be include in all appraisals.

4.11 There is always the possibility that a more extreme flood than the design event will occur during the lifetime of a scheme. Consequently, appraisals should consider all events, not just those up to the design standard of protection.

4.12 An appropriate range of options should be considered. These should normally include:

• different standards of protection;
• alternative alignments;
• different approaches to solution of the problem.

Short-listing a range of options

4.13 Although it is good practice to start with a wide range of options for several different standards of defence, these can usually be reduced to a smaller range of standards and options for detailed analysis. The shortlist of options should include the 'do nothing' and 'do minimum' options; other options are then identified using an iterative process to build up solutions to the problem.

4.14 Any options that are technically inappropriate (e.g. an offshore breakwater to deal with fluvial flooding risk) or technically impractical (e.g. a diversion channel over a hill where there are more sensible alternatives) and options that have real constraints should be screened out. Broad costs and impacts (both positive and negative) of options should be identified; options should then be combined and refined options to reduce the negative impacts and including opportunities to increase the positive impacts.

4.15 The process of valuing options will provide important information on the value for money of different options and, in economic terms, the solution with the lowest present-value cost will be the most cost-effective solution for any particular standard. However, sustainability should be a key consideration, and the option which provides the best solution in environmental terms and options that provide sustainable social benefits should not be screened out unless they are clearly and justifiably unviable.