Nature‐Based Mitigation of Inland Flood Dynamics: Ecohydrological Role of Vegetation Crown Height

Vegetation has been found effective in the mitigation of tsunamis and floods. Nature‐based solutions employing vegetation are increasingly promoted for sustainable flood mitigation; however, the hydraulic role of vegetation structural attributes remains insufficiently quantified under flood‐scale flow conditions. This study investigates the ecohydrological influence of vegetation crown height on inland flood dynamics through controlled laboratory experiments conducted over a range of Froude numbers representative of subcritical to near‐critical flood flows. Physical experiments were performed to investigate parameters like water surface profile, backwater rise, flood energy reduction, fluid and moment force on trees and time‐lapse delay under varying crown height and Froude number conditions. A real‐world vegetation model (Eucalyptus tree) and flood conditions (Pakistan) were replicated using the concept of geometric and Froude similarity. Two vegetation densities (sparse: describes scattered with limited plant cover with significant portions of ground showing, and dense: means plants are tightly packed with little bare ground visible, creating a thick canopy), thicknesses and multiple crown heights (3d–7d (d: vegetation element diameter)) of vegetation were utilized in this study. The results demonstrated that by increasing crown height, the water retention capacity of the vegetation on the upstream side increased up to 87% due to vegetation arrangement. Further, it was observed that a maximum energy reduction of 45% was achieved by increasing vegetation thickness. It was also observed that by increasing crown height from WCS (without crown height for sparse) to 3d‐S (S: sparse) and 3d‐D (D: dense), the fluid force index value decreased up to 58% and 83% for sparse and dense vegetation respectively. A significant delay in floodwater arrival was observed (37%) in the case of a vegetation model with lower crown height compared with other conditions. The findings of the current research demonstrated a significant impact of crown height variation in flood risk management.