Arno’s river flood storage integration landscaping

Year: 2022
Location: Figline Valdarno
Customer: Regione Toscana
Status: Call for tender – Winner
Surface: 120 ha
Partner: Chiarini Associati
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The project involves an area of about 120 ha, mostly flat, located on the hydraulic left of the Arno River and is part of the improvement works for the construction of a flood storage tank. The intervention stems from the need to mitigate the hydraulic risk by using the undeveloped or sparsely built-up areas of the alluvial area located in Restone, in the municipal territory of Figline and Incisa Valdarno. Not a secondary objective was also to reconstitute typical habitats of the floodplain through the insertion of bands of hygrophilous tree, shrub and herbaceous vegetation, with the dual intent of improving the impact of the embankment works on the surrounding landscape, and at the same time, provide benefits in terms of environmental mitigation.

The selection of plant species draws inspiration from the typical flora of the lowland forest, that set of trees that, growing in a lowland location near watercourses, were capable of recharging the water table quite frequently in such a way as not to allow it to deepen more than 5-10 meters. In this sense, the proposed species are capable of withstanding episodes of temporary submergence of the root system and are particularly suitable for inclusion in contexts subject to temporary and probably regular flooding, such as the bottom of flood storage areas.

Specifically, the following native tree species have been selected: English Oak (Quercus robur), White Willow (Salix alba), Black Alder (Alnus glutinosa), White Hornbeam (Carpinus betulus), White Poplar (Populus alba) and Black Poplar (Populus nigra). As shrub and herbaceous species suitable for vegetation on the banks of waterways and marshy areas, the following varieties have been selected: Common Elderberry (Sambucus nigra), Hazel (Corylus avellana), Sanguinella (Cornus sanguinea), Common Privet (Ligustrum vulgare), Dog Rose (Rosa canina), and Marsh Reed (Phragmites australis). The inclusion of the species listed above tends to follow a row-and-group pattern, located mainly between the new southern embankment and the new Restone gully, running longitudinally from the channel of first flood discharge and into the depression adjacent to the agricultural area.

The function of the plants is to contribute to the landscaping of the water storage area, while enhancing its renaturalization by restoring the environmental and ecological value, thus implementing both plant and animal biodiversity. The inclusion of vegetation in the project area will lead to the creation of new habitats of ecological and landscape interest suitable for hosting various bird species, as in the case of the colony of herons (Bubulcus ibis) already present in the area.

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At the landscape-functional level, the new tree plantings will allow better enjoyment of the new bicycle and pedestrian paths along the riverbanks, creating shaded areas for passersby in those areas that are completely sunny. In order to ensure better landscaping of the technical-hydraulic components, the parts of the intake structure that are not subject to immersion, i.e., the parapets, safety barriers and walkways will be made of Cor-Ten steel. The sluice gates and steel parts subject to immersion will be painted in colors similar to Cor-Ten steel in order to make it more uniform and promote the integration of the works in the context. In addition, the planting of shrubs and herbaceous plants around the intake works will further contribute to improve the landscaping and environmental inclusion, as well as the perception of the works itself by the users of the new bicycle and pedestrian paths placed on the banks of the flood storage area.