Nature-based soil and water bioengineering solutions for neophyte control on streambanks - Case study on vegetation related reinforcement of the flood protection project Raababach in Gössendorf, Styria

Keywords: soil and water bioengineering, neophyte control, nature-based solutions, flood protection project, ecological river planning

Abstract: Dominance-forming communities of neophytes arise primarily alongside rivers and cause nature conservation-, economic-, hydraulic engineering- and health-related problems for society. Nature-based soil and water bioengineering (SWB) techniques offer sustainable and adaptable solutions to enable environment friendly interventions. The modes of action are multifunctional and offer the possibility of counteracting complex problems.

The flood protection project on the Raababach in Gössendorf (Styria, Austria) was launched by the State of Styria and implemented in the years 2017 to 2020. The aim was to create flood protection for the neighboring communities and to restore the river Raababach to a near-natural state. The measures were divided into two sections. Section one is characterised by direct intervention in the discharge area. In section two, measures off the stream course were implemented in the form of dams and retention basins.

This case study investigated SWB measures for bank protection implemented as part of the flood protection project (restoration and stabilisation) on the Raababach in Gössendorf (Styria, Austria) and the occurrence of neophytes in section one. The implemented SWB bank protections were evaluated and deviations from the ecological planning were analysed. The number and type of neophytes were mapped and recommendations for action were derived from a four-color rating system. The development of a willow brush mattress (aged 1 y) was recorded in detail and the emerging species were documented. The results of the construction type evaluation and the neophyte monitoring were superimposed and the connections between the selected bank protection and the neophyte incidence were pointed out.

The results revealed that the choice of bank protection, the type of construction design and adjacent areas with a neophyte infestation have an impact on the incidence of neophytes and that specific maintenance measures are necessary. Surface closing construction designs with high initial coverage (willow brush mattress) proved to be favourable for neophyte suppression, while critical stands were surveyed around the area of the concealed stone protection.