This is a specific problem where river velocities increase up to critical velocities for river bed stability. The hazards can be simple river bank erosion causing undercut in the bank, or direct flooding. 

In general, a study on erosion and sedimentation processes includes the characterization of sediment sources (including erosion and remobilization of masses in the river bed), potential movement and consequences both in source areas and depositional areas. Sediment mobility at a specific point, depends of available sediments and local velocity of the water.  It is therefore a time dependent system. 

Flood simulations

The hydraulic model Hec-Ras has implemented sediment transport. These routines will be applied and tested in simulations of Flomselvi and Gudbrandsdalslågen. Existing study of velocities in Flomselvi show a clear relation between observed erosion and flow velocities. A complete numerical Hec-Ras model of Gudbrandsdalen from Mjøsa up to Selsmyrene is expected to be available for research study from mars 2017 (owner Oppland Fylkeskommune/NVE). For sediment transport and erosion, a section of this model will be studied further.

Debris flow in tributaries is usually a major source of course sediments in the main river, and often cause damages on alluvial fans entering the main river. Debris flow can be implemented in RAMMS, and it is useful to test parameters in this model to get realistic forces in order to subsequently design mitigation measures.

Potential contents for WP2 in 2018 and 2019

Work in 2018-2019 could be related to further implementations and applications of HEC-RAS, debris flow in tributaries and flood mitigation.

Flood mitigation is both linked to transport capacity of water and sediment, and movements and sedimentation of sediment. Type of mitigation in this study will be:

Riverbank erosion protection

  • Check dams
  • Sediment dams
  • Removal of bed sediment
  • Debris flow mitigation

The goal of the activity is to be able to give quality advices for river protection Works.