Self-dynamic river widening

This project provides the basis for restoring the morphology of the Gail to the natural state of a gravel river with dynamic banks and pools. This will improve both the ecology of the river and flood protection.

Man sieht den Abschnitt der Gail bei Würmlach aus der Vogelperspektive. Auf beiden Seiten des Flusses liegen Felder.
© eGIS BML

The full title of the project is: Hybrid Modelling for Approximating the Morphological Reference State: A Case Study of the Gail River from Kötschach-Mauthen to Gundersheim. Hybrid modelling means that model calculations on the computer are combined with an objective model in a hydraulic engineering laboratory.

To improve bed stability, river morphology, and consequently the ecology, the Gail River will be widened in several sections. The widening process should occur predominantly through natural dynamics, supported by initial measures only where absolutely necessary. Furthermore, the limitation of channel development through bank protection measures should only be implemented where the natural dynamics would exceed the available space. This approach aims to bring the morphology of the Gail closer to the reference state of a gravel river with dynamic bars and pools. Hybrid modeling will be used to determine how this development process can be secured and implemented as economically as possible. Additionally, the impacts of potential changes in sediment balance due to climate change will be investigated. Some findings from this study will also be applicable to other rivers.

The hybrid modeling aims to answer the following questions:

  1. How does the river's natural dynamic development progress after removing bank protections, assuming average hydrology? In detail, this involves the widening of the river, the development of the river bed elevations and the morphological shape of the Gail. These are all things that will also influence future river ecology.
  2. Are additional initial measures required to promote natural widening? If so, which measures are suitable?
  3. Is there a maximum development width of the river beyond which the Gail does not move or must the entire course of the river in the Gailtal be expected to shift?
  4. Which bank protection measures can limit channel development if necessary?
  5. What influence does sediment input have on morphological development? (What is the impact of significantly reduced sediment input?)

While the objective model is limited to the Würmlach area, the second part of the hybrid modeling, the 1D sediment transport model, covers a significantly larger section (from the Wetzmann power plant in Kötschach-Mauthen to Rattendorf or Watschig). This broader scope serves to better capture the sediment-related boundary conditions for the objective model experiment and to establish a basis for transferring the results to other sections of the Gail River.

The project is being carried out under the direction of our institute in cooperation with the University of Natural Resources and Life Sciences and the engineering office Donau Consult.