Alteration of river flow regimes due to dams result in modifications of riparian ecosystem, with impacts on vegetation, landforms, and habitats. A key characteristic that differentiates riparian zones from adjacent aquatic and terrestrial environments is the event of periodic flooding and water logging. In the regulated Dalälven and other regulated rivers, the Norway spruce (Picea abies) has been seen to replace deciduous hardwood forests over the years due to decrease in the frequency and duration of floods. This thesis aims to gain knowledge on the inundation duration needed to maintain riparian forests with deciduous hardwood trees along the regulated Dalälven. A laboratory experiment was conducted to assess the sensitivity of spruce seedlings to inundation with treatments varying in duration and depth of inundation and level of oxygenation. My hypotheses were that (1) mortality of spruce seedlings would be higher with complete submergence compared to only soils being waterlogged, and that (2) mortality would increase with duration of inundation, and (3) the mortality of spruce seedlings would be higher without oxygenation of water. The data was analyzed by comparing the plant vitality among treatments using analysis of variance using a binary logistic regression. The results indicated that as inundation time increased, the mortality of the seedlings increased. Since the laboratory experiment showed that a large proportion of spruce seedling died after being inundated for 22 and 44 days, reintroductions of floods shorter than the natural spring floods lasting about 1.5 months may be enough to aid in restore riparian forests dominated by oaks and other deciduous hardwood trees, e.g., in the regulated Dalälven river.