Background:
Creating suitable habitat for fish is essential for maintaining biodiversity and ecosystem health in river environments. Among various habitat measures, the strategic placement of rocks has long been recognized as an effective approach to provide shelter and refuge for fish species [1, 2]. However, the current practice of dimensioning and installing these rocks has been based on experience and man-made assumptions, without thorough consideration of hydrodynamics and geomorphic processes. As a result, overdesigned rocks may increase flow resistance, altering the natural hydraulic regime and impeding fish movement, while under-dimensioned rocks may become dislodged and transported downstream during flood events.
Moreover, the unintended downstream transport of rocks during high-flow events poses significant risks to both natural and built environments. These displaced rocks can cause damage to infrastructure such as bridges, culverts, and riverbanks, leading to costly repairs and potential safety hazards. Furthermore, the mobilization of rocks during floods can disrupt the stability of the riverbed, triggering erosion and sediment transport processes and altering channel morphology over time.
An example of rock placement in Frafjordelva river in Rogaland county, Norway. Photo: Ulrich Pulg [1]
Objective:
The objective of this master's thesis is to address these challenges by developing a hydraulic design approach to optimize the dimensions and placement of rocks for fish habitat enhancement in rivers. This approach aims to balance the need for effective habitat creation with considerations of hydrodynamics to ensure long-term stability and functionality.
Key tasks:
- Investigate the influence of different patterns of rock installations:
- Analyze how variations in rock size, shape, spacing, and arrangement affect flow resistance and hydraulic performance.
- Conduct numerical simulations or laboratory experiments (if time permits) to quantify the hydraulic effects of different installation patterns.
- Identify optimal configurations that maximize fish habitat benefits while minimizing negative hydraulic impacts.
- Determine geometric and hydraulic parameters for design:
- Identify key geometric parameters (e.g., rock size, shape) and hydraulic parameters (e.g., flow velocity, shear stress) that influence the effectiveness of rock placement for fish habitat enhancement.
- Incorporate considerations of sediment transport, erosion and stability into the design process to ensure resilience to natural hydrological events.
Optional task:
In addition to the core objectives, an optional task for the student is to develop a practical tool or decision support system to aid in the design process for rock placement in river environments. This tool could be a software application, spreadsheet-based calculator, or graphical interface that allows users to input site-specific parameters and receive recommendations for optimal rock dimensions and placement strategies. By automating aspects of the design process, this tool would streamline habitat enhancement efforts and promote consistency and accuracy in habitat measures projects.
Overall, this master's thesis project offers an opportunity to advance the state-of-the-art in fish habitat enhancement by integrating hydraulic engineering principles with ecological goals, ultimately contributing to the sustainable management of river ecosystems.
References:
[1] | T. Forseth og A. Harby, «Handbook for environmental design in regulated salmon rivers,» Norwegian Institute for Nature Research, Trondheim, 2014. |
[2] | U. Pulg, B. T. Barlaup, H. Skoglund, G. Velle, S. E. Gabrielsen, S. F. Stranzl, E. O. Espedal, G. B. Lehmann, T. Wiers, B. Skår, E. Normann og H.-P. Fjeldstad, «Tiltakshåndboka for bedre fysisk vannmiljø - God praksis ved miljøforbedrende tiltak i elver og bekker,» NORCE, Bergen, 2018. |
Contacts at NVE:
Christy Ushanth Navaratnam (chun@nve.no)
Arne Jørgen Kjøsnes (ajkj@nve.no)