Hydraulic Modelling and Traditional Water Management for Nature-Based Flood Adaptation: A Spatial Planning Framework in the Lower Segura Basin (SE Spain)

Flood adaptation in Mediterranean river basins requires approaches addressing floodwater circulation, redistribution and accumulation. This study proposes an exploratory spatial planning framework integrating two-dimensional hydraulic modelling, official flood hazard mapping and traditional water-management knowledge to identify potential Nature-based Solutions (NbS). Applied to the lower Segura basin (southeastern Spain), HEC-RAS 6.6 simulations used spatially uniform extreme rainfall to analyse water depths, velocities and the depth–velocity index (h·v). Functional hydraulic corridors were delineated using a threshold of h·v ≥ 0.30 m2/s. Comparison of simulated inundation with official SNCZI T500 mapping revealed 106.11 km2 of overlap (31.59%:, 182.42 km2 identified exclusively by the model (54.31%) and 47.34 km2 identified exclusively by SNCZI (14.09%). Qualitative spatial correspondence with traditional boquera irrigation systems and azarbe drainage networks informed a preliminary green infrastructure proposal combining multifunctional corridors, drainage adaptations and Controlled Storage Areas. The framework demonstrates the potential of integrating hydraulic modelling and historical knowledge into territorial flood adaptation planning. However, the simulations were not independently validated, and the hydraulic effectiveness of the proposed NbS remains unquantified.