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dc.contributor.advisorBryan, Karin R.
dc.contributor.advisorPilditch, Conrad A.
dc.contributor.advisorMoon, Vicki G.
dc.contributor.authorNguyen, Hieu Manh
dc.date.accessioned2021-09-14T00:56:43Z
dc.date.available2021-09-14T00:56:43Z
dc.date.issued2021
dc.identifier.citationNguyen, H. M. (2021). Effect of exposure on the erodibility of intertidal mudflats (Thesis, Doctor of Philosophy (PhD)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/14557en
dc.identifier.urihttps://hdl.handle.net/10289/14557
dc.description.abstractSediments on intertidal flats are exposed during low tides. Under the effect of exposure, the water content of sediments decreases because of the evaporation process, which alters the erosive behaviour of cohesive sediments, and therefore changes the patterns of erosion/accretion on intertidal flats. Consequently, exposure indirectly affects the intertidal morphology. An understanding of how exposure alters the erodibility of sediment on intertidal flats is critical to predicting the resilience of intertidal zones into the future during which sea-level rise is believed to exacerbate erosion in low-lying areas. Sediments were collected from an intertidal mudflat in the Firth of Thames, New Zealand in different seasons from 2017 to 2019 for laboratory experiments. Two experiments (Exp. 1 and Exp. 2) were set up in order to explore the effect of exposure including air temperature and exposure duration on erodibility of cohesive sediments. The EROMES device was used to measure the erosion potential of sediment (erosion threshold, Ƭcr N m-2 and erosion rate, ER g m-2 s-1). Exp. 1 investigated erodibility of sediments exposed to a wide range of temperatures (controlled at 0, 8, 25 and 40°C) for 6 h. Meanwhile, Exp. 2 was designed to examine the effect of exposure duration on erodibility. In this experiment, a systematically-changed exposure duration (6 h, 1, 4 and 10 d) was used to mimic a wide range of exposure that might happen on an intertidal flat during a year (set to mimic the Firth of Thames field site). Experimental results indicated that erosion resistance of sediments significantly increased (increased Ƭcr, and decreased ER) corresponding to decreased water content after exposure. The higher the air temperature and the longer the exposure duration, the more stable the sediments were. For instance, the water content of exposed sediments decreased by 1.01 to 1.78 times, a rate which was a function of increasing temperature. The Ƭcr of exposed experiments was 1.2 to 2.2 times higher, whereas ER decreased 1.2 to 6.2 times. After 10 d, exposure increased Ƭcr by 1.7 to 4.4 times and decreased ER by 11.6 to 21.5 times compared with 6 h of exposure. Semi-empirical models fitted datasets from Exp.1 and Exp. 2 were used to predict the variations of Ƭcr and ER as functions of air temperature, T (°C) and exposure duration, D (h). These semi-empirical models were used to extend a Delft3D numerical model to test the effect of exposure on intertidal mudflat profiles and development of tidal channel networks. Model results indicated that exposure enhanced the more flat-topped shape of intertidal mudflats. Higher air temperature resulted in stronger effects on bed level change. For example, for the case of 40°C, bed level built up by 0.039m after one year of model time. Regarding the development of channel networks on intertidal mudflats, the exposure effect tended to create denser and deeper channel networks compared to model runs without the exposure effect. Our findings, therefore, contribute to the prediction of the intertidal morphology development, which will help to understanding the resilience of tidal flats and salt marshes in future under the effect of sea-level rise and global warming.
dc.format.mimetypeapplication/pdf
dc.language.isoen
dc.publisherThe University of Waikato
dc.rightsAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.
dc.subjectthesis with publication
dc.titleEffect of exposure on the erodibility of intertidal mudflats
dc.typeThesis
thesis.degree.grantorThe University of Waikato
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy (PhD)
dc.date.updated2021-09-12T21:30:36Z
pubs.place-of-publicationHamilton, New Zealanden_NZ


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