Abhatoo - Centre Nationale de Documentation

Over 45% of the world surface exists of drylands, that together support over 2 billion people. Despite the importance of drylands, they are often subject to severe land degradation. This is only expected to increase in the coming decades due to climate change, which on the long term affects ecosystem sustainability and economic stability. Restoration practices in these areas are aimed to reduce the effect of local erosion processes. However, current success rates of restoration practices are low, as there is a lack of knowledge on how small-scale erosion processes result in broad-scale geomorphological patterns. Therefore, the objective of this study is to incorporate these relations through a connectivity-network approach, to understand the long-term behavior of sediments within a catchment.
Connectivity - the physical coupling of landforms through geomorphological processes – is used to assess the spatial patterns of water and sediment distribution in the Ounila catchment, Morocco. In the Ounila catchment land degradation leads to a decrease in land productivity and an increase in flood risk. Therefore, the non-profit organization Perma-Atlas started restoration practices. However, knowing where in the catchment their restoration would have a larger effect is crucial in order to maximize the results of their interventions. Therefore, the aim of this research is twofold: first, to gain insight in the functioning of the Ounila catchment and second, to locate areas where geomorphic change will affect the entire catchment (hotspots). The identified hotspots are the recommended locations for Perma-Atlas for the relocation of water- and erosion conservation measures.
In this thesis the concept of connectivity is combined with graph theory, where the catchment is seen as a network of nodes and edges. The benefit of this is that nodes can be hierarchized based on intrinsic properties and corresponding indices of the network. The Network Structural Connectivity (NSC) index is used to analyze the connectivity patterns in the Ounila catchment. Local hotspots are located with the NSC index and insights in the functioning of the catchment are addressed through flow analyses at the outlet of the catchment. Different scenarios are explored to assess the functionality of the proposed method: the effect of spatial extent on the method is investigated and the effect of restoration practices specifically in highly connected areas is quantified. The results from this research show that a connectivity-network approach is a good start to gain the first insights in the functioning of a catchment and to locate hotspots. However, the applied method would benefit from the inclusion of the distances of the sediment pathways. The addition of topological distance would not increase the complexity of the method excessively and is a promising next research step.