Predicting the spatial distribution of mangroves in a South African estuary in response to sea level rise, substrate elevation change and a sea storm event

Abstract. Sandy shorelines are dynamic with constant changes that can cause hazards in developed areas. The causes of change may be either natural or anthropogenic. This paper evaluates evidence for shoreline changes and their causative factors using a case study on the east coast of South Africa. Beach morphology trends were found to be location-specific, but overall the beaches show a receding trend. It was hypothesized that wave, tide, sea level and wind trends as well as anthropogenic influences are causative factors, and their contributions to shoreline changes were evaluated. Maximum significant wave heights, average wave direction, peak period and storm event frequencies all show weak increasing trends, but only the increases in peak period and wave direction are statistically significant. The chronic beach erosion cannot be attributed to wave climate changes since they are still too small to explain the observations. Instead, the impacts of sea level rise and reductions in the supply of beach sediments are suggested as the main causative factors. The analysis also identifies a trend in the frequency of severe erosion events due to storms that coincide with a 4.5-yr extreme tide cycle, which demonstrates the potential impact of future sea level rise.

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Effects of vegetation type on surface elevation change in Liaohe River Delta wetlands facing accelerated sea level rise

Chinese Geographical Science ◽

10.1007/s11769-017-0909-3 ◽

2017 ◽

Vol 27 (5) ◽

pp. 810-817 ◽

Cited By ~ 4

Author(s):

Guodong Wang ◽

Ming Wang ◽

Ming Jiang ◽

Xianguo Lyu ◽

Xingyuan He ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Vegetation Type ◽

River Delta ◽

Surface Elevation ◽

Elevation Change ◽

Liaohe River ◽

Surface Elevation Change

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Disjunct perceptions? Climate change threats in two-low lying South African coastal towns

Bulletin of Geography. Socio-economic Series ◽

10.1515/bog-2016-0005 ◽

2016 ◽

Vol 31 (31) ◽

pp. 59-71 ◽

Cited By ~ 11

Author(s):

Gijsbert Hoogendoorn ◽

Bronwyn Grant ◽

Jennifer M. Fitchett

Keyword(s):

Climate Change ◽

Sea Level Rise ◽

Sea Level ◽

South African ◽

Small Scale ◽

Short Term ◽

Tourist Accommodation

Abstract Coastal towns rely heavily on the quality and expanse of their beaches to attract tourists. Climate is an important tourism determinant, controlling the length and timing of peak arrivals. South African tourism is particularly reliant on these factors. Perceptions of tourists and tourist accommodation establishment regarding climate change threats to tourism are explored for the towns of St Francis Bay and Cape St Francis. Tourism accommodation establishments were predominantly concerned with day-to-day changes in weather, investing in small-scale infrastructural changes to improve the comfort of their guests. By contrast, tourists demonstrated greater concern for the risk of flooding, sea-level rise and the degeneration of the beaches. This reflects concerning disjunctures between perceptions of tourists and accommodation establishments regarding climate change threats. This may portray to tourists insufficient investment in adaptation at accommodation establishments, resulting in decreased tourist visitations in the short-term in favour of destinations perceived as better prepared.

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Processes Influencing Autocompaction Modulate Coastal Wetland Surface Elevation Adjustment With Sea-Level Rise

Frontiers in Marine Science ◽

10.3389/fmars.2021.694039 ◽

2021 ◽

Vol 8 ◽

Author(s):

Kerrylee Rogers ◽

Neil Saintilan

Keyword(s):

Organic Matter ◽

Sea Level Rise ◽

Sea Level ◽

Carbon Storage ◽

Surface Elevation ◽

Vertical Accretion ◽

Elevation Change ◽

Mean Sea Level ◽

Accommodation Space ◽

Surface Elevation Change

The fate of coastal wetlands and their ecosystem services is dependent upon maintaining substrate elevations within a tidal frame that is influenced by sea-level rise. Development and application of morphodynamic models has been limited as few empirical studies have measured the contribution of key processes to surface elevation change, including mineral and organic matter addition, autocompaction of accumulating sediments and deep subsidence. Accordingly, many models presume that substrates are in equilibrium with relative sea-level rise (RSLR) and the composition of substrates are relatively homogenous. A 20-year record of surface elevation change and vertical accretion from a large tidal embayment in Australia coupled with analyses of inundation frequency and the character of sediments that have accumulated above mean sea level was analyzed to investigate processes influencing surface elevation adjustment. This study confirms the varying contribution of addition, decomposition and compression of organic material, and mineral sediment consolidation. Autocompaction of substrates was proportional to the overburden of accumulating sediments. These processes operate concurrently and are influenced by sediment supply and deposition. Vertical accretion was linearly related to accommodation space. Surface elevation change was related to vertical accretion and substrate organic matter, indicated by carbon storage above mean sea level. Surface elevation change also conformed to models that initially increase and then decrease as accommodation space diminishes. Rates of surface elevation change were largely found to be in equilibrium with sea-level rise measured at the nearest tide gauge, which was estimated at 3.5 mm y–1 over the period of measurements. As creation of new accommodation space with sea-level rise is contrary to the longer-term history of relative sea-level stability in Australia since the mid-Holocene, striking stratigraphic variation arises with deeper sediments dominated by mineral sands and surficial sediments increasingly fine grained and having higher carbon storage. As the sediment character of substrates was found to influence rates of surface elevation gain, we caution against the unqualified use of models derived from the northern hemisphere where substrates have continuously adjusted to sea-level rise and sediment character is likely to be more homogenous.

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Coastal wetland substrate elevation is dynamically related to accommodation space and influenced by sea-level rise

10.5194/egusphere-egu21-14069 ◽

2021 ◽

Author(s):

Kerrylee Rogers ◽

Neil Saintilan

Keyword(s):

Organic Matter ◽

Sea Level Rise ◽

Sea Level ◽

Coastal Wetlands ◽

Coastal Wetland ◽

Surface Elevation ◽

Elevation Change ◽

Accommodation Space ◽

Sediment Volume ◽

Surface Elevation Change

<p>The resilience of coastal wetlands in the fate of sea-level rise is proposed to be related to the combined influence of changes in substrate organic matter volume, mineral sediment volume, auto-compaction of accumulating material and deep subsidence; however, relatively few studies have measured all of these variables. In addition, there is ongoing debate about the suitability of this data for modelling the behaviour of coastal wetlands under anticipated sea-level rise projections as temporal discrepancies in the elevation response of coastal wetlands derived from observational and stratigraphic records exist. To resolve these issues, data derived from a range of techniques sensitive to changes occurring at annual, decadal and century timescales, is presented in the context of available accommodation space, that is, the space in which tidally-borne material can accumulate. Focussing on an embayment in Victoria, Australia, analyses confirm that at annual-decadal timescales, organic matter behaves like a sponge, compressing as the overburden of material accumulates, resulting in auto-compaction that modulates the degree of surface elevation change that occurs as tidally-borne material accumulates. These processes operate concurrently and are influenced by sediment availability, yet vary on the basis of available accommodation space. At longer timescales, the influence of auto-compaction diminishes as organic matter has undergone significant compression and decomposition, yet accumulated material remains proportional to available accommodation space. These analyses confirm that temporal discrepancies in rates of substrate elevation change can be resolved by accounting for the timescale over which processes operate and the influence of sea-level rise on available accommodation space. Accordingly, models should dynamically consider rates of surface elevation change relative to available accommodation space.</p>

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