New case study: improving waste modelling for sustainable salmon farming
Investigating limitations in NewDEPOMOD's ability to predict the benthic footprint of organic waste
Scotland’s marine environment is central to its heritage and economy and protecting it is a priority. Fish farming is strictly regulated to minimise ecological impact, with tools like NewDEPOMOD used by SEPA to predict how organic waste settles on the seabed. These predictions help determine farm biomass limits and protect seabed habitats. However, as farms expand into high-energy, dispersive sites, NewDEPOMOD has faced challenged in accurately modelling waste behaviour, prompting this project, known as ‘INCREASE’.
Valued at £195,223, the partners were Cooke Aquaculture Scotland, SAMS, Dalhousie University, and the University of Essex. INCREASE aimed to:
- Investigate how organic waste behaves at dispersive sites.
- Improve NewDEPOMOD’s parameters to better predict environmental impacts under SEPA’s Deposit Zone Regulation (DZR).
Fieldwork was undertaken at three sites in Orkney. Researchers deployed innovative sediment traps to measure waste deposition and resuspension. Results showed realistic patterns of organic waste deposition, aligning with seabed health indicators. However, when tested with NewDEPOMOD’s default settings, the model failed to predict a benthic footprint - most simulated particles dispersed beyond the model domain. Adjusting parameters improved footprint prediction but underestimated resuspension, revealing a key limitation: the model assumes uniform erosion thresholds, ignoring variability in sediment type and organic enrichment.
Findings suggest organic waste erodes more easily from enriched areas and resuspends less when dispersed onto coarse sediments like sand and gravel. This behaviour is not captured by current modelling. Recommendations include updating NewDEPOMOD to allow variable shear stress based on sediment type and enrichment, improving accuracy for dynamic sites.
The project delivered practical benefits: Cooke Aquaculture refined its modelling processes, created specialist roles, and shared insights with SEPA and industry partners in Scotland and Canada. These improvements will support sustainable farm planning, ensuring environmental protection while enabling sector growth.
INCREASE highlighted the importance of robust modelling for responsible aquaculture and sets the stage for future innovations in environmental management.
The full title of this project is ‘INCREASE: Enhancing predictive models for organic waste dispersal’.
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