Flooding is becoming more frequent as rainfall intensifies, prompting growing interest in nature-based approaches that work with the landscape to slow, store and filter water. Temporary storage areas are small features that capture and temporarily hold runoff, typically in rural upper parts of a catchment, before slowly releasing it. However, there is limited evidence on how to design these measures so they perform reliably during large storm events. This research shows that reducing flood peaks requires new, distributed storage that remains empty between storms and is ready to hold runoff when it is at its highest. The Temporary Storage Area Design Optimiser Tool (TSA-DOT) helps tailor designs to local conditions, supporting more reliable nature-based flood storage.
Main Image: An example of an edge-of-field temporary storage area (TSA) intercepting and storing surface runoff and sediment from soil erosion at Tarland. Photo credit: Dr Martyn Roberts, The James Hutton Institute.
Stage
Purpose
Flood risk is increasing as storms become more intense and rainfall patterns change. While traditional engineered defences remain important, there is growing recognition that catchments also need additional storage to slow the flow of water during heavy rainfall.
Nature-based solutions are increasingly used to provide this storage by working with natural landscape processes. One approach involves creating temporary storage areas – small features such as ponds, leaky barriers or wetlands that capture and store runoff, typically in rural upper parts of a catchment, before releasing it slowly. When working well, these measures can delay and reduce flood peaks while also delivering wider benefits such as improved water quality.
In practice, design is often constrained by site conditions. Land availability, soils and topography determine how much water can be stored, meaning practitioners are usually working with a fixed area or volume. The key challenge is therefore to optimise how this storage fills and drains so it slows water effectively during storms.
However, there is limited evidence on how to design these measures so they reliably reduce flooding during large storm events. Storage capacity, outlet design, soils and storm characteristics all affect performance, meaning a one-size-fits-all approach is unlikely to work.
This research therefore asked: How can nature-based flood storage be designed to hold back runoff during storms and reduce flooding in rural catchments?
Examples of small-scale temporary storage areas (TSAs) used in the upper parts of rural catchments (Roberts et al. 2023).
Results
The research showed that temporary storage areas can reduce downstream flooding when enough storage is distributed across a catchment. A review of offline storage ponds found that meaningful reductions in peak flows typically require around 2,000 m3 of additional storage per 1 km2 of catchment (Roberts et al., 2023). If delivered as shallow temporary storage areas (around 0.5 m deep), this equates to just over half a football pitch of storage across a catchment roughly the size of 140 pitches – less than 0.5% of the total area. In practice, this storage would be provided by multiple small features located where runoff from different areas comes together and designed to drain within 24–48 hours.
However, storage only reduces flooding if it is available when it is needed most – during the peak of a storm. Monitoring across multiple sites showed that temporary storage area performance varies through time (Roberts et al., 2024). Drainage rates were influenced by both outlet design and soil conditions. Repeated flooding and sediment deposition reduced soil infiltration, meaning features stayed fuller for longer and had less capacity for the next storm. In contrast, vegetation and appropriate land management helped maintain soil structure and improve flood resilience (Roberts et al., 2025a).
These findings show that effective design depends on balancing storage and drainage. If water drains too slowly, storage may not be available for the next storm; if it drains too quickly, less water is held back. Designs may also need to be adjusted if the aim is to deliver other benefits, such as holding water for longer to trap sediment.
Benefits
This research improves understanding of how nature-based flood storage works in catchments. It shows that effective storage depends not only on how much water can be stored, but on whether that storage is available when runoff is at its highest. By identifying the importance of balancing storage capacity with drainage rates, the study provides clear evidence to support better design of natural flood management measures.
To support practical use, the research developed the Temporary Storage Area Design Optimiser Tool (TSA-DOT). This tool allows practitioners to test how storage capacity, outlet design, soil conditions and storm size influence performance. By enabling designs to be tailored to local conditions, it helps reduce the risk of underperforming measures and increases confidence that they will work as intended.
TSA-DOT: a tool that helps design temporary storage areas (TSAs) by balancing storage and drainage to improve flood reduction during large storms (Roberts et al. 2025b). Acronyms shown: Qin = surface runoff entering the TSA (blue arrow), PET = potential evapotranspiration, and Qout = outflows from the TSA (red arrows).
These findings support climate adaptation and flood resilience efforts. As extreme rainfall becomes more frequent, deploying well-designed temporary storage areas across catchments can complement engineered defences and support more sustainable flood management. By improving design and performance during large storms, this research supports the wider use of nature-based flood storage in rural catchments.
A temporary storage area (TSA) intercepting and storing surface runoff on the Glenlivet Estate. Photo credit: Dr Martyn Roberts, The James Hutton Institute.
Project Partners
Dr Martyn Roberts (The James Hutton Institute)
Dr Josie Geris (University of Aberdeen)
Prof Paul Hallett (University of Aberdeen)
Dr Paul Quinn (The James Hutton Institute)
Dr Mark Wilkinson (The James Hutton Institute)