School for Geospatial Studies and Information Systems

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Browsing School for Geospatial Studies and Information Systems by Author "Du Toit, Louis"

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    Analysing the changes in bathymetry of Saldanha Bay between the years 1977 and 2021
    (2022-04) Du Toit, Louis; Henrico, Ivan; Mtshawu, Babalwa; Stellenbosch University. Faculty of Military Sciences. School for Geospatial Studies and Information Systems.
    ENGLISH ABSTRACT: Possessing one of the finest natural harbours on the South African coast, along with its ideal location on a major international trading route, the Saldanha Bay Municipality has been identified as a key development zone in the blue economy, earmarked to lead major developments in the region. Saldanha Bay is strategically positioned to serve the envisaged oil-and-gas sector on the west coast of the African continent and is a critical area for development for South Africa’s ‘blue economy’. Studies like Henrico & Bezuidenhout (2020) have proven that the changes made during the construction of the Port of Saldanha (PoS) have altered the shape and slope profile of Saldanha Bay (herein called the Bay, which refers to both Inner and Outer Bay, described in section 1.2) significantly, thus changing the hydrodynamics of the Bay. The aim of this study is to compare and analyse the changes in bathymetry of Saldanha Bay between 1977 and 2021. The general tendency of gradual increase in depth from the coastline towards the mouth of the Bay, with sharp increases in depth off Elandspunt and Salamanderpunt, is the same for both 1977 and 2021. The Ordinary Kriging (OK) interpolation method, employed by means of a Geographic Information System (GIS), was selected for creating surface models of the bathymetry of Saldanha Bay, and for conducting the comparison between the two datasets. Said comparison will determine the change in bathymetry over the 44-year period. A slope analysis was also performed to determine the stability of the ocean floor of the Bay. The results of this study indicate a general increase in depth since 1977, with most of the pixels in the graphical representation of the Bay (68.2%) indicating a depth increase between 0.395 - 3.203 m, and an average increase in depth within Big Bay of 1.799 m between 1977 - 2021. There were also two areas identified which experienced changes beyond the standard deviation and showed significant increases or decreases in depth. The general slope trend of Big Bay in 2021 remained fairly like that of 1977, with most of the Bay having a relatively low slope, between 0 - 1.3 degrees. However, in 2021 it can be seen that there is a slight increase in overall slope of Big Bay since 1977, with and average slope of 0.51 recorded in 2021, 0.2 degrees more than in 1977. Furthermore, in 2021 the majority of Big Bay had a slope of 1.3 degrees or less, 0.4 degrees more than in1977. Finally, in 2021 Big Bay also showed an increase in the maximum slope recorded in the Bay, with a maximum slope of 14.8 degrees, more than twice the maximum slope recorded in 1977. The findings of this study support the statements made by Flemming (1977) and Henrico & Bezuidenhout (2020) that the construction of the PoS changed the sedimentation processes within Saldanha Bay to some extent. However, the findings of this study are only relevant for a portion of Saldanha Bay, the inclusion zone in Big Bay as indicated in section 4.3. In this area however, there has been a total loss of 49 364 560.0 m3 in volume. The exact nature and driving forces behind this loss in volume still requires further investigation to be fully understood.
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    Analysing the changes in the bathymetry of Saldanha Bay between the years 1977 and 2021
    (CONSAS Conference, 2022-12) Du Toit, Louis; Henrico, Ivan; Bezuidenhout, Jacques; Mtshawu, Babalwa
    The construction of the Saldanha Port has been the reason for the major changes in the bathymetry and sediment dynamics observed in Saldanha Bay in the last decades. In this paper, newly acquired soundings from the National Hydrographer were used to analyse the changes between 1977 and 2021 - over a 44-year period - in the bathymetry of Saldanha Bay. The Ordinary Kriging (OK) interpolation method, available through the Geostatistical Wizard in ArcGIS Pro, was used for creating surface models to conduct comparisons with the bathymetry of Saldanha Bay. The results indicate a general increase in depth since 1977 of between 0.395 and 3.203 m, and an average increase in depth within the Big Bay of 1.799 m. Between 1977 and 2021, a total volume loss of 49 364 560.0 m3 in sediment was calculated - an indication of how the sedimentation process in Saldanha Bay has changed subsequent to the construction of the harbour.