- 16th April 2018
- Posted by: Joanne Woodhouse
- Category: Projects
Historically, weirs were used to control the water level of rivers to facilitate navigation, permit extraction, prevent sea water intrusion or to power watermills.
In recent years, there has been a reawakening of interest in exploiting weirs as a green energy source, either by building new structures, or retrofitting existing ones with turbines. Concurrently, the EU water framework directive established core environmental objectives that meant no development could compromise achievement of appropriate ecological status; unhindered longitudinal migration of aquatic species is fundamental to successful reproduction for a wide range of aquatic species and therefore in-channel developments, including Hydroelectric Power (HEP) schemes, must demonstrate no negative impact on such migration.
Regulators often require HEP schemes to include structures to facilitate longitudinal fish migration. Knowledge is also lacking regarding the combination of fish passes and HEP outflows on mean and turbulent flow characteristics, and in turn whether these may be modified such that “attraction rates” – the likelihood of an approaching animal successfully locating a fish passageway- may be improved and “delayed passage” may be minimised.
A PhD project undertaken at the Centre for Doctoral Training in Fluid Dynamics at Leeds University and co-funded by the JBA Trust aims to undertake the following:
1. Develop an Eulerian-Lagrangian Agent-Based Model (ELAM) of fish responses to hydraulic (e.g. strain, mean velocity and turbulent pressure driven by the 3-D CFD code;) and other (e.g., chemical, light/shade, sound, temperature;) drivers;
2. Perform bidirectional validation of the coupled model with an existing 2-D fuzzy logic habitat model, JHab, and field datasets from the UK and the Pacific Northwest, USA;
3. Use the coupled models to optimise weir geometries with and without fish passes and HEP schemes. It is likely that no single metric will be appropriate for optimisation, but rather multiple objectives may be sought and traded off (e.g. maximise HEP generation, flow capacity and habitat availability for fish and a range of other aquatic fauna while minimising installation cost and disruption to local people; International Hydropower Association, 2011).
This project aims to strip away at the site-specific nature of the issue by analysing a range of weir, fish pass and HEP geometries in terms of the changes to the pure hydraulics of the river and, by extension, the instream ecology of the river. Further, multiple human factors (e.g. local disruption, economic costs, cultural impacts) may be incorporated and traded off within the analysis framework. The resulting modelling tool should permit an objective analysis to be made of optimum HEP and fish pass arrangements to mitigate against ecological damage. Thus, we hope that the modelling tool will allow developers of both low- and high-head hydropower schemes to design optimised, more sustainable schemes.
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