PROGRAMME

We modelled the effects of flexible and rigid streambed vegetation on river hydraulics and macro-invertebrate habitat suitability in flows/discharges ranging from near-dry to floods, in the Oinoi Stream (Attica, Greece). Vegetation was mapped in spring and summer, simulated using two-dimensional ecohydraulic models (VEGSP: spring model, corresponding to moderate vegetation cover; VEGSU: summer model, corresponding to dense vegetation cover), and the results were compared to those of a non-vegetation-including model (VEGO). Flow velocity (V) was negatively correlated and water depth (D) was positively correlated with vegetation type and density. Compared to VEGO, mean D was 22-40% higher and mean V was 20-34% lower in high/near-flood flows. In low/near-dry flows, V and D were only slightly influenced by vegetation (approx. 10-15% change). Macroinvertebrate habitat suitability (HSI) was higher in densely vegetated areas in both spring and summer, and remained high in near-flood flows, in contrast to the VEGO model (max. HSI change 49.5%). We conclude that streambed vegetation shapes slow-flowing, deeper habitats, and is also a key element for maintaining suitable macroinvertebrate habitats. Ecohydraulic models could be applied to differentiate vegetated river reaches that need flood protection from those that need geomorphic and habitat restoration within accurately designed river management plans.