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Characteristics of and criteria for incipient motion of solid wastes from fish farming
Thesis (MSc)--Stellenbosch University, 2024.
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613879202217984 |
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| access_status_str | Open Access |
| author | Naudé, Francois |
| author2 | Diedericks, G. P. J. |
| author_browse | Diedericks, G. P. J. Naudé, Francois |
| author_facet | Diedericks, G. P. J. Naudé, Francois |
| author_sort | Naudé, Francois |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description |
Thesis (MSc)--Stellenbosch University, 2024. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/131853 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:43:09.148Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/131853 Characteristics of and criteria for incipient motion of solid wastes from fish farming Naudé, Francois Diedericks, G. P. J. Goosen, N. J. á Norði, G. Stellenbosch University. Faculty of Science. Dept. of Mathematical Sciences. Applied Mathematics Division. Aquaculture -- Environmental aspects Fish culture -- Environmental aspects Water pollution Sediment transport UCTD Thesis (MSc)--Stellenbosch University, 2024. ENGLISH ABSTRACT: This study aimed to investigate and determine the physical characteristics of solid wastes from open-cage Atlantic salmon farms with the objective of improving the modelling of the farm waste material. Specifically, the physical characteristics governing the erosion and deposition of the material was investigated, such as the critical erosion shear stress, settling velocity, particle size distribution and density of the waste material. Waste material was sampled from open-cage Atlantic salmon farms in the Faroe Islands directly from the fish using faecal stripping techniques, and from an inland rainbow trout farm in South Africa by collecting pre-settled material. A methodology for determining the critical erosion shear stress of a sample of waste material is presented, whereby the critical erosion shear stress refers to the shear stress at the point of incipient motion, which is where erosion movement starts to take place. An open-channel design, with a false bed, was employed to enable erosion tests with limited available sample material. The methodology proposed, involves calculating the shear stress of material in an open-channel by partitioning the cross-sectional flow area and determining the associated friction of each partition. A method for correcting the effects of the sidewalls of the open-channel was used to calculate the true shear stress acting on the waste material in the open-channel. Incipient motion is considered to take place once a noticeable change in the sediment bed has occurred and is identified by overlaying images of the sediment bed at different shear stresses. A settling tube was designed and constructed to determine the settling velocity of the waste material in terms of cumulative mass fractions. The settling tube was a bottom withdrawal tube, where corrections were made to the settling velocities of each subsequent sample with- drawal to take account of the dropping water level from each sample withdrawal. The results of the settling velocity tests were found to be necessarily expressed in terms of fractions due to their large ranges, rather than being expressed as median or mean values. A sieving methodology was used to determine the entire range of particle sizes and their distributions in terms of mass fractions. The observations from the sampling procedures as well as the particle size distribution of the material indicated a high degree of particle break-up due to the extreme fragility of the material. It is believed that the material should be modelled as a collection of broken particles, rather than intact faecal pellets, as the material spends the majority of the transport journey as broken pieces. The median particle size diameter was determined to be in the range of 400 761 µm for all the rainbow trout and Atlantic salmon samples. Displacement techniques were used to determine the density of the wet bulk material. Moreover, it is shown that the porosity can be calculated from the moisture content of the material, and was so determined. The sediment density and dry density were calculated from analytical relationships relying on the porosity and the wet bulk density. The bulk material was found to be highly porous and had densities much lower than sand materials. The measurements from this study were used in a three-dimensional numerical model of an open-channel in Delft3D-FLOW. The open-channel model was constructed to be directly com- parable to the physical open-channel erosion experiments conducted in this study. The results of the model indicated that the material more appropriately resembled the physical material when the initiation of motion was modelled similarly to that of a cohesive material. This is supported by the physical measurements of the material properties which bear closer similarity to cohesive materials rather than non-cohesive materials. Furthermore, the study concluded that a post-classical modelling approach, whereby an arbitrarily large deposition threshold is adopted, produced simulation results that most appropriately resembled the waste material in this study. While the study proposes a cohesive material modelling approach, with accompany- ing modelling parameters, it does suggest that there may exist a set of modelling parameters, and modelling schemes, that is able to model fish waste material under a non-cohesive material approach with an equivalent accuracy. AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. Masters 2025-04-03T09:11:02Z 2025-04-03T09:11:02Z 2024-12 Thesis https://scholar.sun.ac.za/handle/10019.1/131853 Stellenbosch University xvii, 122 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Aquaculture -- Environmental aspects Fish culture -- Environmental aspects Water pollution Sediment transport UCTD Naudé, Francois Characteristics of and criteria for incipient motion of solid wastes from fish farming |
| title | Characteristics of and criteria for incipient motion of solid wastes from fish farming |
| title_full | Characteristics of and criteria for incipient motion of solid wastes from fish farming |
| title_fullStr | Characteristics of and criteria for incipient motion of solid wastes from fish farming |
| title_full_unstemmed | Characteristics of and criteria for incipient motion of solid wastes from fish farming |
| title_short | Characteristics of and criteria for incipient motion of solid wastes from fish farming |
| title_sort | characteristics of and criteria for incipient motion of solid wastes from fish farming |
| topic | Aquaculture -- Environmental aspects Fish culture -- Environmental aspects Water pollution Sediment transport UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/131853 |
| work_keys_str_mv | AT naudefrancois characteristicsofandcriteriaforincipientmotionofsolidwastesfromfishfarming |