Abstract
There is considerable empirical evidence that using nature-based solutions to restore and enhance hydrological processes such as infiltration, interception, floodplain re-connection and water storage, is effective at small scales for low to medium probability floods. However, the performance of systems of spatially distributed nature-based solutions at larger scales or under the more extreme flooding expected with climate change, has mainly been assessed using modelling. The mechanism by which carefully designed nature-based solutions can provide naturally adaptive pathways to divert higher flood flows into expandable areas of storage in the landscape, has been less formally investigated. This paper reports on new hydrometric data collected from one of eighteen small-scale, accurately monitored micro-catchments in Cumbria, UK, to study the effect in more detail. The micro-catchments have been set up by Lancaster Environment Centre as part of the Q-NFM project attempting to quantify changes in hydrological responses due to a range of natural flood management measures that have been installed by catchment partners. A direct-runoff 2d inundation model was setup and calibrated using accurate flow measurements upstream and downstream of new river restoration project in the Lowther catchment (2.5 km2) for two large storm events (Storms Ciara and Dennis, February 2020). It was used to analyse how the storage on the floodplain can expand with flood magnitude, and can be enhanced with appropriately designed natural flood management. Model evidence was then assessed for the same mechanism in the larger UK catchments of Eddleston Water (70 km2) and Culm (280 km2) using the same whole-catchment direct-runoff modelling approach. For both of these large catchments the same expandable field storage is evident, and we highlight how this latent property of well-designed nature-based solutions can complement traditional strategies and provide significant economic benefits over a thirty-year appraisal period of the order of €0.7 m.
Highlights
Nature Based Solutions are considered to provide natural resilience to climate change extremes [25], helping to reduce further warming, supporting biodiversity and securing ecosystem services [3,4,8,23]
The micro-catchments have been set up by Lancaster Environment Centre as part of the Q-NFM project attempting to quantify changes in hydrological responses due to a range of natural flood management measures that have been installed by catchment partners
With little empirical evidence for flood risk reduction at larger scales [6], it is difficult to understand the limits of effectiveness of NBS in combination with other traditional risk reduction measures without relying upon broadscale modelling evidence [11,12]
Summary
Nature Based Solutions are considered to provide natural resilience to climate change extremes [25], helping to reduce further warming, supporting biodiversity and securing ecosystem services [3,4,8,23]. In recent modelling studies it has been noted that certain types of NBS keep working at higher and higher flows, providing land scape storage and additional resilience to climate change [15] This is unlike embankments or defences, which provide a design standard of protection, which as the loading increases beyond this, it could be argued do not ‘keep on working’ to reduce risk. Natural adaptation pathways develop from using leaky barriers, woody material, bunds and floodplain reconnection techniques in order to connect flows of increasing magnitude to field storage [19], but the fact these areas are often expandable is overlooked Their integrated impact on attenuating peak flows is complex, and there are strong benefits from whole-system modelling. Pushing more and more water into expandable areas of storage on the floodplain can help with other integrated measures, for example water resources if the areas of new storage are above permeable geology this can promote additional recharge
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