Improving the Hydromorphology of Alpine Rivers in the Provision of Ecosystem Services through Responsible, Resilient River Restoration

In mountain regions, competing demands for use are concentrated along rivers in mostly narrow valleys. After systematic channelization and sediment retention by transverse structures in the catchment massively impaired biodiversity as well as direct human uses, and after the condition deteriorated further due to riverbed incision, river widening emerged as an effective countermeasure. With increasing awareness of the ecosystem services (ES) provided by a functioning hydromorphology and in order to reduce the bedload input required for bed stabilisation, the provision of corridors is recommended for channel widening. There, the hydromorphology can develop freely and is thus mainly determined by the bedload supply. However, the required amount of bedload that would ensure the functionality of the hydromorphology to provide the ES needed today and the associated space requirements are unknown. HyMo4us! first surveys the historical and current uses along Alpine rivers. For a study section of the Drava, a hydromorphological laboratory model is deployed to search for the bedload input, which results in a morphology corresponding to the historical condition. Based on the morphology and morphodynamics recorded in detail, ES such as habitat provision, flood protection, groundwater supply and offers for recreational activities are determined for these conditions. Subsequently, the results of the laboratory model are used to identify the range of bedload input, which creates a hydromorphology that offers ES according to the surveyed human demands. Additional investigations of major flow events indicate the resilience in the provision of ES under climate change-induced changes in hydrology and bedload input, and serve to narrow down the target bedload input. Following the hypothesis that the width distribution of a natural channel is related to the depth transverse distribution, regression analysis is used to try to exploit the potential of historical maps for calculating a historical bedload transport as a natural reference. The resulting bedload and space requirements will be analysed with an experienced planner for feasibility, and a dialogue with policy makers on the weighting of current uses will be promoted. The results will lead to a guideline that will be made available as a support for current river development and risk management concepts. The development of didactic material together with pupils and a training course offered for teacher training colleges promote a responsible approach to the hydromorphology of alpine rivers across generations.