A research report submitted to the Faculty of Engineering and the Built
Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment
of the requirements for the degree of Master of Science in Engineering.
Johannesburg, 2018 / The use of boulders to create habitat heterogeneity is important for aquatic
diversity, and being able to predict the stability of a boulder that is placed in a
river will aid in sizing the boulder. Identifying ways to increase the stability could
save costs associated with over design or replacement due to the boulder washing
away. Existing research on incipient motion centres on determining threshold
conditions for bed material or protruding elements within a bed surface with
relation to, among others: shape of particle, size of particle, relative depth of
particle to flow depth, and impact of channel slope. The existing research is
limited to bed material that is of a similar size and there is no research on the
conditions for incipient motion elements that are relatively large compared to the
bed material it is resting on. An idealised flume study was performed to identify
trends that several factors have on boulder stability, as well as to verify the results
obtained from a pivoting analysis model prediction for a spherical boulder. An
additional study was performed to obtain drag coefficients that were suitable for
use on spherical boulders that were either embedded into the bed material or
simply resting on top of the bed material. The results of the drag experiments
were varied; only the results for the non-embedded were suitable to integrate into
the model predictions while drag coefficients for the embedded boulders need to
be taken from previously published results. The results of the flume study
provided good confirmation of the model predictions with the average absolute
experimental error being 4%. The trends identified in the flume study show that
the most effective method in improving a boulder’s stability is to embed it into the
bed material with this being more effective than increasing the size of the boulder. / MT 2018
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/25739 |
| Date | January 2018 |
| Creators | Stols, Kevin |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (xiv, 98 leaves), application/pdf, application/pdf, application/pdf, application/pdf |
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