Navigation

SEDRIVER: More floods – more sediment transport – less fish?

 

Climate change has an impact on sediment movements in mountain rivers. The researchers developed a model simulating bed load transport in mountain rivers. They also investigated how bed load changes affect the river trout.

Project description (completed research project)

Climate change will have an influence on run-off behaviour and the transport of sediment in mountain streams. Heavier precipitation is expected, which will lead to more intensive flooding, probably with higher sediment delivery. There will also be a time shift in the run-off over the course of a year. These changes will influence the habitat and the development of river trout populations. The SEDRIVER project examined the possible effects of climate change on the transport of sediment and on river trout in mountain streams.

Methods

The researchers developed the sedFlow model in order to simulate bed load transport in mountain streams. The model uses a simplified run-off calculation to determine the long-term bed load transport in the channels of Alpine catchment areas. Sudden sediment delivery, for example as a result of mudslides, can also be taken into consideration here.

Field examinations in several Swiss mountain rivers determined the length of the spawning period, the habitat utilisation of the spawning animals and the burying depth of river trout eggs. Local characteristics, mesohabitat utilisation in summer/autumn and the occurrence of trout were examined in three sections of the Kleine Emme. The MEM mesohabitat evaluation model was also used for these three sections.

According to a run-off model based on climate scenarios of the C2SM research group of the Swiss Federal Institute of Technology in Zurich (ETHZ), the run-offs in the Kleine Emme and Brenno catchment areas will increase in winter in the future. This run-off data was fed into the sedFlow simulation model. This enabled the researchers to examine possible effects on the bed load transport and the river trout. Scenarios were also created for extreme flooding and sediment delivery.

Results

The spawning period of the river trout starts at the end of October and lasts until the beginning of January. The average burying depth of the eggs is roughly 4 cm. This figure is considerably lower than shown by previous examinations in lowland streams.

The sedFlow model was used to simulate the future erosion depths in winter. The results show that these will hardly increase in the Kleine Emme and the Brenno in the near future (2012-2050); nevertheless, they will increase significantly in the longer term (2070-2099), above all in the Brenno. This increasing erosion depth is a problem during the spawning period, and is a threat to the survival of the eggs and the freshly hatched trout. During this sensitive phase in the life of river trout, the deepest level of the river bed is likely to occur at a later time than in the control period, especially in the distant future. However, the results of the examination in the Kleine Emme permit the conclusion that the smaller run-offs in summer could lead to a greater habitat diversity with more low-water areas for young trout.

The effects of mudslides on the transport of sediment were examined by means of scenarios on the Brenno and the Hasliaare. The results showed that the effects on bed load transport in the vicinity of a tributary differ depending on whether the sediment delivery from the mudslide is continuous or sudden. Also important is whether the sediment delivery takes place at an early or late stage during flooding.

Significance for research and practical applications The expected impacts of climate change can have both positive as well as negative effects on the habitat and development of river trout. On the one hand, the increasing erosion depths are a threat to the natural reproduction of the species. On the other hand, lower run-offs in summer in future could in part create favourable habitat conditions for young trout. However, the habitat and the development of river trout are also influenced by other factors, such as river training works, renaturation measures as well as the expected increase in water temperature as a result of climate change.

The new approaches implemented in the sedFlow model for calculating bed load transport should assist experts and decision makers in assessing risks in Alpine catchment areas. On this basis, sustainable maintenance and protection concepts can be developed.

Relevance for research and practice

The expected impacts of climate change can have both positive as well as negative effects on the habitat and development of river trout. On the one hand, the increasing erosion depths are a threat to the natural reproduction of the species. On the other hand, lower run-offs in summer in future could in part create favourable habitat conditions for young trout. However, the habitat and the development of river trout are also influenced by other factors, such as river training works, renaturation measures as well as the expected increase in water temperature as a result of climate change.

The new approaches implemented in the sedFlow model for calculating bed load transport should assist experts and decision makers in assessing risks in Alpine catchment areas. On this basis, sustainable maintenance and protection concepts can be developed.

Original title

Effects of climate change on mountain streams (SEDRIVER)

Project leaders

  • Dr. Dieter Rickenmann, Eidg. Forschungsanstalt für Wald, Schnee und Landschaft WSL
  • Dr. Armin Peter, Fischökologie und Evolution, Eawag Dübendorf
  • Dr. Jens Martin Turowski, Gebirgshydrologie und Wildbäche, Eidg. Forschungsanstalt für Wald, Schnee und Landschaft WSL

Partner project

A partner project at the EPF Lausanne financed by the Federal Office for the Environment FOEN and conducted by Prof. A. Schleiss investigates the influence of the altered sediment availability on the risk of failure of flood protection measures in alpine rivers. Further on, strategies to encounter these new risks of failure will be examined. Cost-benefit functions and different aspects of sustainability will be of special interest in this context.