SUPERVISOR: Thomas HEIN

PROJECT ASSIGNED TO: Damiano BALDAN

Nature Based Solutions (NBSs) aim at targeting water-related issues of river catchments by supporting the restoration of natural processes and cycles. The planning and evaluation of the effectiveness of NBSs for river restoration can take place at different spatial scales (catchment, reach, site). Three challenges hinder an effective planning of NBSs: a) the incorporation of hierarchic multi-scale interactions in the assessment of spatiotemporal arrangement of the ecosystem components, e.g., sediments, landforms, and biota; b) the use of semi-mechanistic tools to project stream-scale responses; c) the projection of ecosystem responses to management interventions across different spatial scales and extents.

In this thesis, an Ecohydrological Modeling cascade (EMC) was developed to fill these gaps, including a catchment scale hydrological model (SWAT), reach scale hydraulic models (HEC-RAS), a site scale Random Forest Ensemble (RF) to predict the risk of occurrence of Fine Bed material Deposits (FBMDs), and Specie Distribution Models (SDMs) for the endangered Freshwater Pearl Mussel (FPM) habitat. The models were implemented and calibrated for the Aist catchment (630 km2) in Austria.

In the first study, the EMC was used to assess life-stage specific constraints for an effective FPM conservation plan in the studied catchment. In the second study, the impacts of climate change on the FPM during his life stages were propagated with the EMC, revealing FBMD being likely an issue in the future because of the occupancy of suitable habitat and the reduction of dispersal likelihood between suitable habitats. In the third study, the effectiveness NBSs for mitigating FBMDs risk was assessed, revealing: a) the effectiveness to be highly variable and dependent on the analyzed scale and spatial extent; b) combination of NBSs to be most effective in reducing FBMDs risk. The use of a model cascade improved the parameters identifiability and allowed for easy transferability of the models.

This thesis supports the implementation of NBSs for river restoration by a) coherently project impacts and responses at multiple spatial scales and extents in a catchment; b) projecting the effects of NBSs that are not directly located in the streams on important ecosystem components (i.e., FBMDs, and the Freshwater Pearl Mussel). The implementation of NBSs for mitigating the FBMDs issue can also lead to synergies of soil conservation, species conservations, and climatic goals, beneficial for river management.

Keywords: Modeling River Systems, Spatial Scales, Nature Based Solutions, River Restoration, Fine Bed Material Deposits, Freshwater Pearl Mussel