"Delivering ecosystem resilience in the face of climate change is essential if we are to stand a chance of preventing an increase in the speed of biodiversity decline, yet alone improve the condition of our rivers to achieve the condition required under current and future legislation.
One of the most effective ways of returning natural process and increasing resilience is by removing weirs and redundant water level controls to improve both longitudinal and lateral connectivity, something which is recognised in publications supporting river restoration designers, such as Natural England’s Climate Change Adaptation Manual and the CaBA Biodiversity Pack.
When designing weir removal schemes and preparing documentation to obtain regulatory authority approval, we must demonstrate that the impacts of climate change have been taken account of when it comes to flood risk. But how often do we consider the impacts of climate change on flows, or ecological and geomorphological processes when making design decisions?
CEH’s Enhanced Future Flows and Groundwater (eFLaG) Portal indicates that, for example Q90 flow on the River Don at Doncaster might be between 40% and 60% less than current in the near future (defined as between 2020 and 2049; current baseline was considered up to 2018).
In the world of fish pass design, a reduction in flow at Q90 of between 40-60% is significant, meaning difficult decisions around which species are most important to accommodate may need to be made, and whether the delivery of performance criteria at low or high flows is more important. I would suggest such difficult decisions need to be addressed head on to ensure that funding is spent wisely, the solutions implemented do not have a limited life span and do not result in unnecessary carbon emissions.
Similarly, whilst in-channel shear stresses might not change significantly as a result of climate change, do we understand how sediment transport might change at a catchment scale to enable that to be sufficiently considered in restoration scheme design?
I would also offer a mild challenge as to whether there is sufficient understanding and consensus amongst the regulatory authorities, fisheries and geomorphology staff on this and related issues. In its most recent annual fisheries report, the Environment Agency stated it is keeping a ‘watching brief’ on climate change as a research area relevant to fisheries. However, I feel more needs to be done to prioritise understanding on these small but significant, technical details.
To ensure we’re raising awareness of the issues and tools available, as well as delivering against our own resilience to climate change framework, our Hydroecology team is committed to raising the issue of climate change in design hydrology determination on all new projects. For more information on how we plan to achieve this, please contact Jonathan Whitmore.