Fluvial Design Guide - Chapter 1

Design of works in the fluvial environment


1.5 Principles of fluvial design

Box 1.2 sets out some of the principles to which good practice fluvial design should adhere. Further details and basic information to underpin these statements are provided in Section 1.4.

Box 1.2 The eight principles of fluvial design

1. Fluvial design must be sustainable. It must aim to work with natural processes and meet the needs of the present without compromising the ability of future generations to meet their own needs. Consequently, all fluvial design work must aim to:

  • avoid negative impacts to the river system and users of it;
  • be efficient in its use of resources;
  • maximise opportunities for win–win scenarios.

2. Fluvial design must consider all stages in the lifecycle of the intervention – not only its primary role during its operational life, but also the construction stage at the beginning, its operational and maintenance requirements, and the decommissioning stage at the end.

3. Fluvial design must include engagement with all stakeholders from the early stages of a project. This allows early identification of project opportunities and risks. It also helps to ensure that nothing is overlooked, reduces the risk of conflicts arising, and promotes ‘ownership’ of the project, which may be important once when the scheme is in operation.

4. Fluvial design must adopt a systems approach. It has to look at the complete river system insofar is it can be affected by, or may have an impact on, the proposed interventions. This includes potential interaction with surface drainage systems.

5. Fluvial design must be performance-based. It has to take account of the mechanisms that can cause failure of the assets to perform as intended. This is relevant for defence assets and their function to defend against flooding, but also for watercourses and their function to convey water. It is also relevant for other functions such as facilitating navigation or improving aquatic habitat.

6. Fluvial design must consider the full range of loading conditions that the asset is likely to meet in its design life. Traditionally the practice has been to adopt a design condition such as the 1% annual probability flood and to focus exclusively on this. Such an approach is no longer acceptable and the designer must examine both lower flow conditions (which are much more likely to occur) and extreme floods beyond the design event, in order to reduce the risk of catastrophic failure and other adverse impacts.

7. Fluvial design must be flexible and adaptable. We cannot accurately predict the future, particularly in terms of global climatic change. Designs should therefore be flexible and adaptable so that changes can be made readily at a later date, if necessary, rather than fully designing now in an attempt to meet an uncertain future requirement.

8. Fluvial design must take account of the inherent uncertainty associated with natural events and our understanding of them. Designs should be robust and resilient, so that they provide the required level of service now and in the future.


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