The Vulnerability of Walvis Bay to Rising Sea Levels

P. Hughes, G.B. Brundrit, S. Searson

Abstract


The potential impacts of rising sea levels on the harbour town of Walvis Bay on the Namibian coast are considered. Walvis Bay is an arid, semi-desert environment with most of the town lying 2 m above mean sea level. The town is sheltered by 8 large sandy spit from the prevailing wave climate, which, on the open coast, can be quite severe. The area has an exceedingly dynamic sediment budget and is completely reliant on a small coastal aquifer for freshwater. This paper demonstrates the vulnerability of semi-sheltered environments to sea level rise and the need for accurate sediment budgeting in any Potential Impact Assessment. Four categories of potential impact are considered; increased coastal erosion, flooding and inundation, increased saline intrusion and raised water-tables and lastly reduced protection from extreme events. The effect of increased coastal erosion is found to have limited impact on the town but the remaining three potential impacts could have serious consequences, especially the threat from extreme events. Nine years of hourly tide gauge data were analysed using the Joint Probabilities Method and water level return frequency curves were drawn. A 20 cm rise in sea level was found to be sufficient to raise the annual occurrence water level to above that of a current 1 in 100 year event. A future 1 in 10 year storm, after a 20 cm rise, would attain a higher water level than that which could be reached by a 1 in 1,000 year event now. This Potential Impact Assessment provides an analogue for other environments which may be sheltered from the effects of coastal erosion such as low lying tidal inlets and estuaries.

 

 


Keywords


Sea-level rise; Walvis Bay; Bruun Rule; extreme water levels; joint probabilities method

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