Spatial and Temporal Variations in Arable Soil Structure and Hydrology Affect the Functioning of Nature-Based Solutions for Flood Mitigation

Temporary storage areas (TSAs) are nature-based solutions designed to mitigate flooding and soil erosion by creating dispersed catchment-based storage to attenuate surface runoff during storm events. While the uptake of TSAs is increasing, their hydrological function can vary over time. To better understand the factors influencing time-variable TSA functioning, this study investigated how TSA soil physical and hydraulic properties respond to temporal events such as land management practices and flooding, and how these responses vary spatially across land uses and within TSA footprints. For two typical TSAs on arable land in NE Scotland, we monitored rainfall, TSA water levels and soil moisture over 2 years. Bulk density, macroporosity and saturated hydraulic conductivity were measured on 6 to 7 occasions within TSA footprints and adjacent contributing areas. Soil structural degradation following flood inundation and minor sedimentation was most pronounced within the TSA footprint, particularly in bare arable soils. Soil structural changes varied spatially across field management zones and between intermittently flooded and non-flooded areas. They also differed temporally in response to seasonal conditions and tillage. For example, macroporosity decreased from 0.16 m3 m−3 post-tillage to 0.07 m3 m−3 post-winter and saturated hydraulic conductivity was lower in TSA soils (6.1e−5 ± 1.6e−4 m s−1) compared to contributing areas (1.8e−4 ± 1.3e−4 m s−1) post-flood. Tillage temporarily improved topsoil structure and hydraulic properties but increased vulnerability to slumping and erosion when poorly timed relative to flooding. In contrast, vegetated TSA soils maintained more favourable physical and hydraulic properties post-flood, indicating greater resilience. Although downstream flood impacts were not quantified, the results improve understanding of the dynamic soil and hydrological processes that influence TSA functioning over time. Reduced infiltration capacity due to soil structural degradation may limit available surface water storage within TSAs, affecting their ability to attenuate surface runoff during storm events. Recognising these spatial and temporal changes can inform management strategies that help maintain or enhance TSA hydrological functioning for effective surface runoff attenuation.