Grain size analysis, coastal hydrodynamics and erosion protection: a case study from Knysna and Plettenberg Bay, South Africa

Pezisa, Ayabulela Raymond

Title: Grain size analysis, coastal hydrodynamics and erosion protection: a case study from Knysna and Plettenberg Bay, South Africa
Creator: Pezisa, Ayabulela Raymond
Subject: Grain -- Analysis
Subject: Hydrodynamics
Subject: Shore protection
Date: 2022-12
Type: Master's theses
Type: text
Identifier: http://hdl.handle.net/10353/27698
Identifier: vital:69394
Description: The modern beach sands and Cretaceous Knysna Formation distributed along the coast of Plettenberg Bay and Knysna coast in the Western Cape Province of South Africa, have been examined and studied in the field outcrops and laborataries via grain-size analysis, XRD, SEM, EDX and microcope petrography analyses. This study looked into the coastal hydrodynamics and environment protection. The project aims to investigate the sediment distribution, grain-size variation, sedimentary structures, coast erosion and mitigation in the Plettenberg and Knysna coast to address environmental issues in the south coast of South Africa. The research will provide new insight onto coastal sedimentation, hydrodynamic condition, coastline erosion and the safety of the coastal environment and human property. The study will promote government attention on the sea level change, which caused flooding and environmental disaster along the south coastal area of South Africa. The rock sequence in the inland side of the study areas belongs to Cretaceous Knysna Formation, which comprises seven upward fining sequences. The stratigraphic sequence is underlain by the Table Mountain quartzite of the Cape Supergroup, and is overlain by Tertiary sediments and modern coastal dune sands. The Knysna Formation at the research area consists of massive conglomerate, sandstone and minor mudstone of mainly fluvial dominated sediments. The grain size analysis reveals that the modern fluvial channels at Plettenberg Bay and Knysna areas are of dominant coarse sands with minor silt and mud, which defines the sediments were deposited by moderate to high energy currents. Whilst the beach zones in Plettenberg Bay are predominated by fine to medium-grained marine sands. Grain-size analyses of beach sands show well-sorted, fine to coarse skewed in grain size distribution, indicating a relative lower to medium uniform energy condition during transportation and deposition. The bivariate plots of grain-size distribution demonstrate of the shallow agitated marine environment with the influence of tide and aeolian processes. Hydrodynamic condition in the beach area was more persistant and less variation compared to the river environment. The mineralogy and petrology studies revealed that in Plettenberg Bay and Knysna sediments are predominantly consisted of minerals quartz, feldspar, calcite, muscovite, aragonite, clay minerals, and salts (halite). Skeletal carbonate minerals (shell and coral fragments) are more than chemical precipitated carbonate minerals. The microtextures detected on the surface of the fluvial and marine sand grais involve V-shaped pits, upturn pits, dissolution pits and secondary mineral precipitation that were created by chemical and mechanical processes formed via sea-water dissolution, corrosion, and transport crashing. Whereas the boring holes and burrows created by activity of microorganisms boing into the surface of the grains. These microtextures of the river and beach sands exhibit a shallow marine and fluvial environments with medium to high energy conditions and active organic activities. Several sedimentary structures were detected in the coastal environments, including various types of ripple marks and dunes, burst bubble-hole, swash line, rill marks, rhomboid marks, burrows, boring and bioturbation, planar lamination and gravel pavement. In addition, sedimentary structures were also identified in the Cretaceous Knysna Formation such as air/water escape hole, convolute bedding, lenticular bedding, tabular cross-bedding and load cast. The sedimetnary structures closely linked with hydrodynamic conditions and therefore can be used as indicators for depositional environments. Flooding and erosion had become a coastal disaster that results in sediment redistribution throughout the coastal system and therefore caused landscape reform like coastal cliffs and sharpened dunes in erosive areas. Particularly, coastal hazards become more and more serious in recent years due to climate and sea leavel changes. Thus, to recognise coastal erosion and disaster and make a management strategy is of significant importance to compete against coastline retreat and to protect infrastructure and human safety in the coast area. The author had proposed a number of mitigation methods for environmental protection and for combating coastal erosion, including breakwaters, groins, jetties, vertical walls, rock armour, vegetation, boundary hardening, and revetment etc, which are the effective ways for protection of coast retreat, property damage and human safety.
Description: Thesis (MSci) -- Faculty of Science and Agriculture, 2022
Format: computer
Format: online resource
Format: application/pdf
Format: 1 online resource (xviii, 209 leaves)
Format: pdf
Publisher: University of Fort Hare
Publisher: Faculty of Science and Agriculture
Language: English
Rights: University of Fort Hare
Rights: All Rights Reserved
Rights: Open Access

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