Student´s corner

Proposed topics for Master theses and research ideas for BSc and PhD:

What trees can tell us to improve our understanding of fluvial processes and flood risk assessment?: Trees are robust environmental archives that record and store the conditions where they grow. Extracting this information requires combining different techniques (e.g., geomorphology, dendrochronology, chemistry). This project will use trees, forest patterns and the state as proxy data to improve our knowledge about flooding processes and related phenomena in selected mountain rivers.

Why does sediment grain size matter in rivers?: In mountainous streams, sediments play a decisive role in aquatic fauna habitats. Moreover, the sediment (bedload) size provides crucial information about the sources of sediment, the erosion and transport mechanisms and the flow regime of these streams. This work aims to understand better the factors controlling sediment grain size and how this varies across a range of river morphologies and lithologies. To do so, the sediment grain size will be measured in the field at selected mountain streams, and data will be related to morphological and hydraulic variables.

How does the riparian vegetation protect rivers from widening during floods? How much do rivers widen? And where will they do so?: Channel widening is the dominant geomorphic response to floods and an essential process that sustains fluvial ecosystems, but it might pose a hazard in highly populated rivers. Therefore, identifying where major channel widening occurs is paramount for flood risk and river management. The presence of vegetation influences channel width and bank erosion, but understanding how to preserve it to protect from channel widening is limited. The project will combine fieldwork, remote sensing and statistical analyses in rivers affected by past floods.

How do changes in flow-, sediment- and wood- regimes affect fluvial dynamics and riverine habitats?: Geomorphic conceptualizations of rivers emphasize that the diversity of form and process through space and time reflects the flow and sediment regime; however, the instream wood regime is missing in this conceptualization and needs to be stressed. This is the goal of this project. However, explicitly incorporating wood regime in our understanding of rivers is challenging because wood is supplied, transported, and stored by complex processes operating at temporal and spatial scales that differ from water and sediment. Humans have also highly altered the three regimes. Numerical modelling opens the door for investigations of how changes in the water, sediment or wood regime may affect the fluvial response (in terms of geomorphic and habitat changes), which is fundamental for river management. This project will apply a scenario-based approach to a numerical model combined with field observations to explore the response of different types of rivers to disturbances (e.g., floods) and different scenarios of flow, sediment and wood regimes.

Connectivity, process coupling, sediment and wood sources and supply in mountain rivers: Connectivity and process coupling are vital issues in rivers function. Hillslope-channel coupling plays a fundamental role in controlling catchment sediment dynamics. This project will apply and enhance the concept of connectivity, which provides an overarching framework to better explore how catchments function and make it possible to include sediment and the wood sources and potential paths (i.e., cascades) through the stream network.

How and when is instream wood mobilised in rivers? How much wood can be expected during a flood?: Flow and sediment regimes are two of the main abiotic factors driving riverine ecosystems, interacting at different temporal and spatial scales. The instream wood regime has been only recently defined as the third leg of the river´s systems tripod. The wood regime consists of wood supply, transport, and storage in river corridors. These processes can be characterised in terms of magnitude, frequency, rate, duration, and mode. However, data to quantify the wood regime is very scarce. Thus, the first long-term monitoring framework with a network of cameras and tracking devices is deployed in Swiss rivers to monitor instream wood fluxes. The gathered data will help to analyse the rate, volume and timing of instream wood transport, which is, like sediment, a central question to many applications in river science and engineering.

How much wood, wood-induced sediment and organic carbon are stored in alpine rivers?: In mountain rivers, instream wood accumulations are related to the formation of steps and pools, which modify the longitudinal slope of river channels. The wood jams form obstacles that lower the flow velocity, affect turbulence and thus influence the storage and sorting of sediment. Instream wood accumulations enhance the accumulation of finer sediment that would otherwise be flushed downstream. The quantification of sediment retention by instream wood accumulations in rivers has only been attempted in a few studies in the US. It was observed that wood could retain between 49 and 81% of the total stored sediment within a river network. The sediment retained by instream wood in Alpine rivers has never been estimated. This work aims to fill this gap; to do so, sediment storage related to instream wood accumulations will be estimated in the field at selected mountain streams.

Where does instream wood come from? Can the source be inferred from tree rings?: The environment where trees grow leaves a footprint into the tree. Tree rings can be used to reconstruct past disturbances (e.g., floods) and to trace where the tree grew even after being uprooted and transported as instream wood. We will determine wood origin in rivers by applying dendrochronology (i.e., tree rings), dendrochemistry, and developing fingerprinting approaches.

Dam reservoirs as observation windows for instream wood regime: This project will quantify the amount of driftwood that accumulates in selected reservoirs, using the Planet satellite imagery and analysing the wood amount variations with discharge and flood information and computing instream wood transport rates.

How is the current ash tree dieback affecting rivers?: The ascomycete fungus Hymenoscyphus fraxineus (synonym: H. pseudoalbidus, basionym: Chalara fraxinea) is a new invasive pathogen causing severe dieback of Fraxinus spp in Europe. In Switzerland, the disease was first reported in 2008 in the northwest, from where it expanded rapidly to other regions. The influence of this disease on instream wood supply, decay and storage are unknown. This project aims at characterizing the effects of Fraxinus dieback on river systems and particularly on instream wood supply by applying remote sensing and field surveys.

Interested in rivers, floods, trees…? You are welcome to propose your project! If you are interested in doing research with us, do not hesitate to contact us.

More information:

Faculty of Geosciences and Environment

Master in Environmental Science

Master in Biogeosciences

Master of Science in Geography