1

DRAFT

RECENT EXTREME EVENTS ALONG THE COAST OF SOUTH AFRICA

Andrew Mather1 and Andre Theron2

1mathera@durban.gov.za Contact person

2CSIR

ABSTRACT

INTRODUCTION

The coast of South Africa is continually exposed to hazards from the sea, which

threaten the well-being of coastal communities through loss of infrastructure and

services, and have important and long-lasting social, economic and environmental

implications. In recent years, extreme events from the sea have caused much

damage all along the coast, and a state of emergency has had to be declared in the

worst affected areas. The unfortunate experiences of 2007 and 2008 all around the

coast have now been repeated in 2011 in the southern and eastern parts of the

country. Civil authorities are concerned to know whether these recent extreme

events are a foretaste of what the future might hold under climate change. In such

circumstances, they also wish to learn from these recent events so as to better cope

in the future, and to build resilience against any increase in these hazards from the

sea onto the coast.

After providing the context of hazards and marine drivers along the coast of South

Africa, an overview is given of recent intensification of extreme sea levels and wave

events, and an assessment of the prospects for the future is made. Observations of

two recent extreme events are detailed, and the lessons that can be learnt from the

experiences gained from these events are enumerated. The paper ends with

recommendations for the development of a Coastal Hazard Exposure Classification

along the coast of South Africa.

HAZARDS IN CONTEXT

Indicators of coastal vulnerability almost all relate to parameters that measure

erosion and inundation along the coast (Theron et al 2010), and the main drivers are

waves and sea water levels (Van Ballegooyen, Theron & Wainman (2003)). The

focus on inundation and erosion leads to the identification of seven variables (coastal

2

relief, lithology and landforms, and relative changes in sea level, shoreline

movement, tidal range and exposure to large waves) for hazard assessment. On the

South African coast, beaches, estuaries and lagoons can be identified as potentially

high risk environments because of their unconsolidated soft sediments, low relief and

wide inland exposure. It should be noted that such areas account for more than 50%

of the South African coast, and these sections of coast are generally eroding rather

than accreting (Tinley, 1985).

Relative changes in sea level along the South African coast are consistent with

global sea level trends, with little evidence of any appreciable local land subsidence.

Tides around the South African coast are remarkably uniform, with a meso-tidal

range of just over 2 metres and generally weak tidal currents all around the coast. By

contrast, the wave climate is robust and large waves can penetrate right up to the

coast everywhere. Statistics of significant wave height (the average of the one-third

biggest waves measured in a twenty minute period) exceed 4 metres for 10% of the

time and reach 8 metres annually, in deep water along much of the coast of South

Africa. Such large waves possess considerable erosive power and, if coastal

defences are breached, the land behind is easily inundated.

INTENSIFICATION OF HAZARDS

Extreme inshore sea water levels

Significant drivers of high inshore sea water levels are tides, wind set-up, hydrostatic

set-up, wave set-up and, in future, sea-level rise (SLR) due to climate change

(Theron, et al 2010). These drivers all affect the still-water level at the shoreline. The

drivers/components of extreme inshore sea water levels most significant to the

Southern African context are the tides (South African spring tides are about 1 m

above mean sea level (MSL), but reach up to +3.7 m MSL in Mozambique), potential

SLR, and wave run-up. Theron (2007) has estimated that in the South African setting

during extreme events, these components could each contribute additional amounts

(heights) of between about 0.35 m to 1.4 m to the inshore seawater level. Note that

potential additional impacts of climate change (e.g. more extreme weather events) on

wind-, hydrostatic- and wave set-up are not included in the above.

3

Recent observations from satellites, very carefully calibrated, are that global sea

level rise over the last decade has been +3.3+/- 0.4 mm/y (Rahmstorf et al, 2007)).

The IPCC AR4 Report (IPCC, 2007) concludes that anthropogenic warming and sea

level rise would continue for centuries due to the timescales associated with climate

processes and feedbacks, even if greenhouse gas concentrations were to be

stabilised.

Comparisons between about 30 years of South African tide gauge records and the

longer term records elsewhere, show substantial agreement. A recent analysis of sea

water levels recorded at Durban confirms that the local rate of sea level rise falls

within the range of global trends (Mather, 2007). Present South African SLR rates

are: west coast +1.87 mm.yr-1, south coast +1.47 mm.yr-1, and east coast +2.74

mm.yr-1 (Mather et al. 2009).

The probability of sudden large rises in sea level (possibly several metres) due to

catastrophic failure of large ice-shelves (Church and White, 2006) is still considered

unlikely this century, but events in Greenland (Gregory, 2004) and Antarctica

(Bentley, 1997; Thomas et al, 2004) may soon force a re-evaluation of that

assessment. In the longer term the large-scale melting of large ice masses is

inevitable. Recent literature give a wide range of SLR scenarios, but most

“physics/process based” projections for 2100 are in the 0.5 m to 2 m range (Rossouw

and Theron, 2009; Nicholls and Cazenave, 2010; Palmer et al. 2011).

4

Figure 3.1: Measured and projected sea level rise over the 20th and 21

st centuries. The red curve is

based on tide gauge measurements, the black curve uses the altimetry record from 1993-2009, and the

shaded light blue zone represents IPPC AR4 projections. Vertical bars are semi-empirical projections.

(Nicholls and Cazenave, 2010).

The drivers of inshore water levels should not be confused with the added effect of

wave run-up which, in the South African context, can reach much higher elevations.

Wave run-up is the rush of water up the beach slope beyond the still-water level in

the swash zone. According to surveyed elevations (Mather et al. 2011), maximum

run-up levels on the open Kwazulu-Natal (KZN) coast near Durban during the March

2007 storm (which coincided with the highest tide of the year) reached up to about

+10.5 m MSL. Note that wave set-up and run-up are both accounted for in these

levels.

Around Southern Africa, wave run-up is thus clearly the dominant factor, which may

be considerably exacerbated by tides and future SLR (Mather 2011).

5

Wave climate

Much research is being done at a global level to determine if the wave climate is

changing. Mori et al. (2010) examined the oceans using a General Circulation Model

(GCM) and they found from their analysis clear regional dependences of both annual

average and also extreme wave heights from present to future climates. The results

highlighted that the future wave climate is predicted to increase at both middle

latitudes and the Antarctic Ocean but reducing at the equator.

Preliminary findings indicate that there may be long-term trends in regional metocean

climates, while sea level rise alone will greatly increase the risks and impacts

associated with extreme sea-storm events (Theron, 2007). The regional variation in

the global wave climate was demonstrated by Mori et al. (2010), who predicted that

the mean wave height might generally increase in the regions of the mid latitudes

(both hemispheres) and the Antarctic ocean, while decreasing at the equator. Their

study was based on simulating future trends. Further evidence of a general wave

height increase in the northern Atlantic, along the North American East coast was

provided by Wang et al. (2004). Komar and Allan (2008) also found an increase in

the wave height generated by hurricanes along the East coast of the United States

using wave data from the National Data Buoy Center (NDBC) wave buoy data.

Investigations done by Ruggerio et al. (2010) with buoy data, also indicate increasing

storm intensities along both the West and East coast of Northern America. There are

significant similarities in the general wave climate of the northern and southern

hemispheres if comparisons are made between equivalent northern/southern

hemisphere latitudes (Rossouw and Rossouw 1999). Thus, general changes in

northern hemisphere wave climate could be expected to be mirrored by similar wave

climate changes at equivalent latitudes. Such changes in the regional metocean

climates are expected to have significant impacts on local coastal areas. It is

therefore important to also investigate possible future climatic changes off the

southern African coastline as well as the expected associated impacts (Theron,

2011).

As can be anticipated, a more severe wave climate (or indirectly a more severe

oceanic wind climate) will have greater impact on run-up and flooding levels and will

thus necessitate the prediction of future trends in the wave climate. Although the

available wave record is shorter than ideally required to determine long-term trends,

6

a preliminary analyses was conducted (Theron et al 2010). It was found that the

annual mean significant wave height (Hm0) and corresponding standard deviation for

the wave data set collected off Richards Bay and the annual mean wave height (Hm0)

for the long-term data set, collected offshore of Cape Town, indicate no real

progressive increase. This may appear to contradict the findings of the IPCC as

presented in PIANC (2008). However, the South African results may reflect a

regional aspect of the impact of climate change.

Although the averages appear to remain constant, there seems to be some change

in the individual storms (Theron et al 2010). For example, considering the peaks of

individual storms during the more extreme winter period (June to August), an

increasing trend of about 0.5 m over 14 years is observed (Figure 3.2). The trend

may be indicative of a significant increase in the “storminess” over the next few

decades. It is also worth noting that the opposite occurs during summer: there is a

general decreasing trend over the last 14 years with regard to individual storms.

Offshore Cape Town - Winter

Individual storm above 5 % exceedance value (4.9 m)

0

2

4

6

8

10

12

1-Ja

n-94

1-Ja

n-95

1-Ja

n-96

31-D

ec-9

6

1-Ja

n-98

1-Ja

n-99

1-Ja

n-00

31-D

ec-0

0

1-Ja

n-02

1-Ja

n-03

1-Ja

n-04

31-D

ec-0

4

1-Ja

n-06

1-Ja

n-07

1-Ja

n-08

31-D

ec-0

8

1-Ja

n-10

Date

Hm

o (

m)

Figure 3.3 Peaks of individual storms over 14 year-period – offshore Cape Town

(based on recordings by CSIR on behalf of TNPA).

If the apparent trend is indeed true, storminess in terms of intensity, may be on the

increase. To some extent it could be said that the preliminary trend indicated by the

7

South African wave data is supported by the model predictions of Mori et al. (2010),

which appear to show (Figure 3.3) an increase for the South African coast of roughly

6% (at exceedance probability < 10-5).

Figure 3.3: Future wave climate changes from model predictions by Mori et al.

(2010)

At the regional scale there have been a number of investigations. Guastella &

Rossouw (2009) examined the wave record at Slangkop, off Cape Town and

Richard’s Bay and found that the wave measurement record indicates that, while

there has been a slight increase in storm intensity at Slangkop during the winter

season, there has been no discernible change in number of storm events over the

time series record. At Richards Bay the intensity of exceedance events has remained

fairly constant, but there has been an overall increase in number of exceedances

over the measurement period however Corbella (2010) who examined the wave

climate in detail at Durban and Richard’s Bay was unable to find statistically

significant trends.

Tropical cyclones

Climate change projections also indicate that cyclones may become more intense

(IPCC, 2007). Tropical cyclones are another major threat along the Mozambican and

KZN coast. About 2 cyclones per year enter the Mozambique Channel, while about

1 cyclone per year makes landfall in Mozambique. The cyclone tracks over the

Mozambican channel, since 1952 to 2007, are illustrated in Figure 3.4

8

Figure 3.4: Cyclone tracks during the November to April period for the years 1952 to

2007 in South-west Indian Ocean (Mavume et al., 2008)

Three of the five extreme tropical cyclones in the last 50 years that have tracked

unusually far west into southern Africa, also occurred during La Niña years. In all

cases, warm sea surface temperatures (SST) anomalies near Mozambique and

pronounced South-western Indian Ocean (SWIO) high pressure anomalies led to a

strong westward steering current, favouring the inland penetration of the tropical

cyclones (Reason et al., 2004). Climate models predict that certain trends will

continue into the 21 century (Saenko et al., 2005): Further intensification and

southward shift of the high-latitude westerly winds with an affiliated increase in the

Antarctic Circumpolar Current transport; Southwards migration and intensification of

the southern hemisphere sub-tropical gyre circulations; Further warming of the

southern hemisphere oceans between latitudes 40° to 50°S, with increased off-

equatorial subsurface upwelling and cooling between latitudes 5° to 10°S for the

Indian Ocean.

Ridderinkhof et al. (2010) found that increasing the intensity of the south equatorial

current (SEC) leads to a strengthening of the Tropical Gyre during La Niña periods,

which in turn leads to a strengthening of southward flow transport through the

Mozambique Channel. Interpretation of such evidence and models indicate that

extended La Niña events may reflect the future ocean state of the SWIO (Rossouw &

Theron in prep). A southward shift of the cyclone belt resulting from these changes

would mean an increase in the occurrence of cyclones (and waves generated by

9

these cyclones) in the southern Mozambique and North-eastern SOUTH AFRICAN

coastal regions (Alan Meyer, CSIR, pers. com.).

Mavume et al. 2010 examined the frequency of cyclones between the months of

November to April in the western Indian Ocean and concluded that in recent years

(1994-2007) there has been an increase in the number of intense tropical cyclones

compared to an earlier period (1980-1993). However when a longer period is

considered (1952-2007) the research shows a decrease in both the number of

cyclones and the number of cyclones which make landfall. Since the mid 1960’s the

number of cyclones in both the South Western Indian Ocean and the Mozambique

Channel have been decreasing.

If the prognosis is that wave heights will increase in the future then what will be the

impacts of this intensification.

Impacts on sediment transport and coastal erosion

Using various empirical formulae, Theron and Rossouw (2008) have calculated that

a modest increase of wind speeds of just 10% would result in a 26% increase in

wave height, an 80% increase in wave power (wave power is proportional to the

square of the wave height and linearly proportional to the wave period) and a 40 to

100% increase in cross-shore sediment transport rates, thus increasing the

vulnerability of coastal areas to erosion. Theron and Rossouw (2008) have further

suggested that a 50% increase in erosional volume, could very roughly be translated

to a potential 50% increase in horizontal shoreline erosion distance.

TWO INDIVIDUAL EXTREME STORMS

KZN STORM 2007 Map needed?

The coastline of KZN is vulnerable to significant erosion due to its exposure to both

cyclonic induced wave events as well as the winter swell waves associated with the

southern oceans. A number of historical events have impacted this coastline and the

more recent notable events have been the wave event in 1966 which scoured large

amount of sediment from beaches near the Umbogintwini River (Juckes 1976), the

large swell event produced by tropical storm Imboa (1984) with a significant wave

height (Hs) of 9 m (Guastella & Rossouw, 2009), the large wave event off East

London in 1997 with an Hs of 9.3 m (Guastella & Rossouw, 2009), and the most

10

recent and arguably most destructive wave event in March 2007 (Mather 2011). In

recent times, the most significant period of erosion along the KZN coastline has been

the years 2006 and 2007 where this erosion was driven by a series of large cyclonic

induced wave events (Smith et al. 2007). The peak erosion and destruction

culminated during the March 2007 storm which affected approximately 400 kms of

coastline and which occured just after the lunar nodal cycle peak maximum tides

(Smith et al. 2010).

THE BUILD UP TO THE MARCH 2007 COASTAL EROSION EVENT.

This extreme wave event, generated by a stationary low-pressure system off the

coast, occurred when tide levels were almost at the 18.6 year peak of the Lunar

Nodal Cycle. This combination resulted in exceptionally high waves on top of a

raised sea level causing widespread damage along the entire KwaZulu-Natal coast

on the 19 and 20 March 2007. The Saros equinox spring tide had been identified as

early as September 2006 as a possible period of vulnerability from increased erosion

for the Durban coastline and in particular for properties located north of Durban along

Eastmoor Crescent, La Lucia (Mather 2006).

Sea conditions prior to the event had been unseasonable, and the sea had been

unsettled with swells in the range of 2 to 3 m. The prevailing sea conditions prior to

March had been influenced by three tropical cyclones (Dora, Favio and Gamede)

located east of Durban. Of these, only Cyclone Dora and Gamede were significant.

Cyclone Dora, which later combined with a well-developed cold front to the south,

induced swells in the 2-3 m range and impacted Durban on 11th to 13th February.

Cyclone Gamede arrived several weeks later as this storm tracked westward towards

Madagascar on 26th February, turned southward on 28th February and eventually

stalled in the south Indian Ocean from 1st to 6th March. Despite being downgraded

from a cyclone to an extra tropical depression cyclone Gamede was responsible for

the first calls of concern from residents as it generated 2 to 4 m swells from 1st to 5th

March. This event caused local inundation and minor erosion along Durban’s golden

mile (the beachfront strip from the harbour entrance to the Umgeni river mouth) when

these swells coincided with the spring high tides on 3rd to 4th March. Minor erosion

damage was also recorded up and down the KwaZulu-Natal coast.

11

THE STORM OF 19th-20th MARCH 2007

The storm started as a frontal low, which passed south along the coast of South

Africa on 16th March. The frontal low intensified and rapidly developed into a cut-off

low south-east of East London on 17th and 18th March and from the dense isohyets

around this low, it can clearly be seen to intensify to a peak on the 19 th March where

it remained trapped between two high-pressure cells until the 20th March. The system

started to weaken by midday on the 19th March and was almost back to normal by

20th March.

The central pressure of this low-pressure cell dropped to below 996 hPa. The strong

pressure gradient between the low and high cells generated strong and consistent

winds, which were recorded between 40 knots (21 m/s) and 45 knots (23m/s) along

the coast. As the system was trapped in position this allowed the wind to generate

some impressive waves over the fetch length of ±450kms straight at the coastline of

KwaZulu-Natal. The Acoustic Doppler Current Profiler normally used to record wave

heights in Durban was out of commission during this event. Recorded wave heights

for the event are therefore confined to the CSIR wave-rider buoy located off Richards

Bay in 30m of water depth. This recorded a significant wave height (Hmo), defined as

the average of the top third waves recorded, of 8.5m, with a period 16 seconds from

the south-east to south-south-east, measured at the peak of the storm at 05h00 on

19 March (Rossouw M, pers. comm.). The maximum wave height was recorded at 14

m (Rossouw M, pers. comm.). At the same time, the highest spring tide of the year

occurred. This would have elevated water levels by approximately 20cm more than

the normal spring tide levels and when synchronised with the wave event magnified

this combination. Fortunately, the wave event very quickly dissipated and by the

evening of the 20 March, the swells had reduced to less then 3m. After the storm,

wave run-up heights were measured at twelve beaches along the Durban and Ballito

coastline and these peaked at +10.57 m above MSL (Mather 2011).

CAPE STORM 2008 Map needed?

This extreme event occurred along the western and southern coast during the period

31st August to 4th September 2008 with deep water significant wave heights of 10.7

m. Based on the recorded wave data, it is estimated that this storm had a return

period of about 10 years (Theron et al 2010). A frontal weather system developed

12

approximately 600 km south-west of Cape Town and then a secondary low pressure

zone then grew as an example of “explosive cyclo-genesis” (Hunter, pers comm.

2008). The secondary low migrated in a north-easterly direction causing damage

along approximately 1200 km of the South African coastline between Cape Town

and Port Elizabeth. The high waves also coincided with high tide levels since the

duration of the storm was longer than 12 hours and the event occurred only one day

after spring tides. It is also worth noting that on the 31st August the water level

exceeded the astronomical predicted tidal level during the storm event. In False Bay,

the actual water level (as recorded in Simons Town Harbour) was about 0.5 m above

the predicted level, and about 0.7 m in Algoa Bay, most likely the effect of the storm

surge, which in this case is a combination of the wind and wave setup as well as the

barometric effect (but excludes wave runup in these cases).

Recorded wave heights for the event are from the CSIR wave-rider buoy located off

Slangkop in 70m of water depth. Significant damage to harbours, fishing craft,

coastal infrastructure and transportation systems occurred due to the event Figs 3.5

and 3.6). After the storm, wave run-up heights were measured at seventeen beaches

around the Cape Town coastline and these peaked at +7.9m above MSL (Mather

2011).

Figure 3.5: A breakwater barely coping with the September 2008 storm waves at present water levels

(Photo: A Theron)

13

Figure 3.6 Damage to Port Elizabeth rail lines in the September 2008 storm (Photo M Hoppe)

LESSONS LEARNT FROM THESE WAVE EVENTS

A number of lessons were drawn from the experiences of these two events and the

lessons below have been drawn from two papers by Mather (2006) and Breetzke et

al. (2008) namely:

Lesson 1: Interventions should be co-ordinated.

What was obvious from the responses during and after these storms was that

nobody was prepared and this resulted in much wasted time and effort in taking

things forward. In fact the public were very vocal and came out saying

“The … municipalities along the coastline do not seem to have the initiative to be pro-

active and in fact seem unable to deal with the problems like the recent storm events

very well, even in a reactive way”

“… our only hope for the long-term sustainability of our coastline is for …[capacitated

municipalities] to lead the way, work out with the necessary expertise exactly what is

needed, what is available, and then drive this at a Provincial level, so that Province,

possibly through the Provincial Coastal Committee and Regional Coastal

14

Committee…get this information implemented along the coastline through the

various municipalities”.

The local authority has a duty of care to ensure that whatever is proposed is

sustainable and that each property owner is not left to his or her own devices to

construct a patchwork of different protection systems. Local authorities should

encourage a co-ordinated or co-operative approach by affected property owners. A

Municipal Coastal Management Programme, incorporating Shoreline Management

Plans, is required to reduce the direct and associated effects of erosion (ICM 2009).

Lesson 2: Accept and live with coastal erosion

As was shown in Section 1 sea levels are rising around the South African coastline

and this will result in the erosion of the shoreline. The threat to property will continue

to increase under these circumstances and the hard lesson is deciding when to

“throw in the towel” and retreat inland.

Lesson 3: Flat sandy coastlines are the most vulnerable

While the coastline of South Africa is dominated by sandy shorelines, there are

sections of shorelines that can be classified as rocky. These rocky shorelines

experienced some minor erosion however sandy coastlines, particularly those with

low gradient coastlines, were severely affected. Exposed low gradient sandy

shorelines will need to be carefully dealt with given their ability to retreat by up to

40m in width under extreme storm conditions. In fact, in specific circumstances

where the source or supply of sediment to a beach area is interrupted or largely

reduced, short-term erosion in the order of even 100 m or more is possible in some

areas (as evidenced by observations).

Lesson 4: Managed retreat must be considered first before any reconstruction is

considered.

Current International Best Practice in the face of sea level rise is a managed coastal

retreat. Managed coastal retreat will combat the increasing risk of coastal erosion

and damage due to sea-level rise. The removal of structures and movement back

inland providing a larger space for the fluctuation of the shoreline to occur and will

reduce the risk of infrastructural damage and ultimately prevent regular repeated loss

of this infrastructure thus underpinning the concept of sustainability.

15

Lesson 5: Establish a coastal set back line.

A development setback line is designed to protect both the natural environment from

encroachment from buildings as well as protecting beachfront developments from the

effects of storms and accelerated coastal erosion.

Lesson 6: Sand has been lost so sand must be replaced.

The storm has removed beach sand therefore the best replacement material is

beach sand provided the grain size is of the correct order. This might sound obvious

but as has been evidenced by well meaning efforts of people trying to protect their

properties, many have taken to dumping various types of material in the eroded

beach with little regard to the effects of this action.

Lesson 7: Soft coastal systems need “soft engineering” solutions.

The optimum erosion buffer is a natural dune cordon system. These should be

established wherever additional protection is required. Property owners should be

encouraged to re-establish and rehabilitate the dune systems between their

properties and the sea. Where replication of the natural dune cordon is problematic,

the use of soft-engineered, artificial vegetated dunes can be considered. Replaced

sand can be stored within geofabric bags angled back up the erosion slope

preventing further sand loss at the toe of the dunes and allowing some wave run up

over the sloping structure thereby reducing the wave energy.

Lesson 8: Hard engineering should only be employed as a last resort.

“Hard” engineering should only be employed as a last resort as this causes local

erosion and down-drift erosion. Hard engineering in this case is defined as any

structure that is constructed from hard materials not likely to be commonly found in

the beach zone. Examples of this are concrete sea walls, steel trench sheeting and

contiguous augered pile walls. Hard vertical barriers are the worst performers in

terms of reducing wave energy at the interface. The high-energy wave comes into full

contact with the vertical face and reflects back into oncoming waves creating

turbulence, which caused a loss of sediment at the toe of the sea wall. While the

structure can be designed to withstand this, the effects are that the loss of sand at

the toe is not replaced as easily as a similar stretch of beach without a sea wall. This

leads to a locally sand starved environment preventing the full recovery of the beach

16

and its associated sand dunes because the material is usually transported offshore

or down-drift and not recovered.

Lesson 9: Be prepared, monitor and react

Coastal property owners should prepare for erosion events by purchasing and

storing appropriate sand bags. Coastal property owners should monitor coastal

change and react accordingly in an emergency, i.e. immediate threat to human life or

health, property or any aspect of the environment. Appropriately reconstruct coastal

infrastructure and amenity. Coastal property owners, in collaboration with affected

Municipalities, remain responsible for the removal of rubble as a result of coastal

erosion. Infrastructure that is damaged as a result of coastal erosion should not just

be replaced. Its appropriateness should be assessed and necessary improvements

made, and in the medium- to long-term, plans prepared and implemented for a

managed retreat of such infrastructure. Coastal amenity such as concrete lifesaving

facilities that have been damaged should be replaced with more appropriate “softer”

solutions, e.g. temporary wooden lifesaving towers.

Lesson 10: Avoid and reduce risk

Coastal property owners are responsible for the maintenance of storm water

discharge and liable for any erosion or negative impact such discharge may have on

the frontal dune or beach. Where storm water has to be discharged onto a dune,

such discharge should be away from the dune face and toe. Discharge should

preferably be onto a hardened area such as a rocky headland. Integration of storm

water systems between neighbours should be encouraged.

ADAPTATION

Much of the focus is now on adaptation, Theron et al (2011) focused on specific

adaptation measures and coastal protection options available to mitigate abiotic

climate change impacts in African developing countries. Examples of coastal

protection measures and management options, that they considered to be

appropriate to southern Africa, included:

Management options, which include “accept and retreat”, “abstention”,

“alternative” coastal developments and “accommodation”, as well as aspects

of integrated coastal management (ICM) planning.

17

“Soft engineering” or restoration, which entail “semi-natural” interventions in

the littoral zone, such as sand nourishment, managed (vegetated and/or

reinforced) dunes, increasing the density or extent of mangrove or wetland

areas, and protecting coral reefs.

“Hard engineering” and armouring, which involve the construction of shore

protection measures, including conventional and unconventional structures or

measures. At least eight types were considered suitable for exposed sites,

while some four were considered only suitable in low to moderate wave

energy environments.

Theron et al (2011) also presented evaluation criteria to guide decision making on

the appropriate response and a comparative functionality/suitability analysis of

potential adaptation measures.

Mangor et al. (2011) are preparing a guideline titled ”Mitigation of coastal erosion

along sandy coasts” which is aimed at less developed countries and how these

countries can prepare themselves for coastal erosion.

INSURANCE ISSUES

In recent years the insurance industry has started to take a keener interest in the

impact of climate change in the region. The insurance industry has started

undertaking risk assessment along the coastline (Morris, J. pers. comm.) in an

endeavour to understand their potential exposure to future losses. Unfortunately

these studies are very often not made public and therefore cannot be used to

manage potential future impacts. After large claim events like the 2007 KZN and the

2008 Cape wave events the exact extent of insurance pays outs is difficult to

establish however there has been a number of sites which were damaged during

these events which Insurers have now deemed “uninsurable” given that the certainty

of a similar event and damage is only a matter of time.

DEVELOPMENT OF A COASTAL HAZARD EXPOSURE CLASSIFICATION

Fortunately, due to the relief of much of the South African coast and the location of

existing developments, relatively few developed areas are sensitive to flooding and

inundation resulting from projected SLR at least till the year 2100 (Theron and

Rossouw 2008).

18

Work by Midgley et al. (2005) has identified a number of vulnerable coastal areas

(resulting from climate change impacts) within the Western Cape Province. The

ongoing migration of people to coastal areas will worsen the impacts.

SOUTH AFRICAN Coastal and marine hazards

Van Ballegooyen, Theron & Wainman (2003) identified all significant

marine hazards relevant to the Western Cape.

From this hazard inventory it can be said that all of these “natural”

hazards result from either erosion and/or underscouring, flooding and

inundation, direct wind and wave impacts and occasionally currents

and, broadly speaking, algal blooms and pollution.

Focussing on the abiotic risks to infrastructure and developments in

the coastal zone, the main metocean drivers are thus waves and sea

water levels (and to a lesser extent winds and currents in some

instances).

This is generally confirmed by the literature on coastal vulnerability

assessment methods, in that the indicators almost all relate to

parameters that affect vulnerability/resilience to erosion/under-

scouring, and flooding/inundation (Theron et al 2010).

19

The methodologies recently developed and applied in Portugal and Spain have a

practical approach and are well-suited to the South African context. Jimenez et al.

(2009) have developed good coastal storm vulnerability assessment methods, but

the input data requirements are considered to be too onerous for wide scale

application in the Southern African context. Jimenez (2008) provides a good

description of how coastal vulnerabilities can be assessed for multiple hazards. From

a literature study (Theron et al 2010) it was concluded that the set of parameters

included in the method developed by Coelho et al. (2006) would be pragmatic and

most relevant for application to the Southern African coast.

The first part of the Coelho et al (2006) method is to assess the degree of exposure

and vulnerability to coastal processes using nine indicators as the basis. Specific

limit values associated with each of the indicators were defined and the assessment

Primary SOUTH AFRICAN Coastal Abiotic Hazards and Marine

Drivers

The primary hazards to (physical) coastal infrastructure related to sea

storms are:

Direct wave impacts

Coastal flooding & inundation

Erosion & under-scouring

Focussing on the abiotic hazards to infrastructure and developments in the

South African coastal zone, the main metocean drivers are thus:

Waves

Sea water levels

Winds (to a lesser extent)

Currents (to a lesser extent and in much fewer instances)

It is the combination of extreme events (sea storms occurring during high

tides in conjunction with sea level rise) that will have the greatest impacts and

will be the events that increasingly overwhelm existing infrastructure (Theron

et al 2010).

20

is done by selecting the appropriate range of values for each indicator. A vulnerability

classification of Very Low (Vulnerability Score = 0 -1) to Very High (Score = 4- 5) is

then derived. Three additional indicators, relevant to the Southern African coast,

were identified by Theron et al (2010) and added to the Coelho et al 2006.

assessment methodology. In the tropics (e.g. Mozambique) two important additional

indicators have been included by the Authors: cyclones and corals/fringing reefs.

In general the most vulnerable South African coastal areas (resulting from predicted

climate change impacts) that have been identified to date Theron et al (2010) are:

Northern False Bay

Table Bay

Saldanha Bay Area

The south Cape coast, Mossel Bay to Nature’s Valley

East London

Port Elizabeth

Durban

North of Richard’s Bay

The developed areas of the Kwazulu-Natal south coast

Apart for the potential losses of beach areas it is predicted that by 2100 South Africa

would lose some 11% of its wetlands due to adaptation interventions such as coastal

protection measures and structures erected to mitigate sea level rise impacts. This

will make South Africa the 5th most vulnerable country worldwide to wetland losses

resulting from sea level rise by 2100 (Tol 2004). With these potential problems

looming there is consideration being given to extending the work of Theron et al.

(2010), and of Palmer et al. (2011), to produce a national South African coastal

vulnerability assessment and this will be covered.

REFERENCES

Breetzke, T., Parak, O., Cilliers, L., Mather, A.A. and Colenbrander, D. 2008. Living

with coastal erosion: a short term best practice guide, Proceedings of the

International Association of Impact Assessors South Africa conference.

21

Corbella, S. 2010. A review of Durban’s wave climate and storm induced shoreline

changes. Unpublished MSc., University of KwaZulu-Natal, Durban.

Guastella, L.A. and Rossouw, M. 2009. Coastal vulnerability: are coastal storms

increasing in frequency and intensity along the South African coast?. Proceedings of

the 6th International Multi-Purpose Reef Conference, Jeffrey’s Bay, South Africa.

Juckes, L.M. 1976. A Bone-bearing beachrock at Umbogintwini, Natal. TranSouth

Africanctions of the Geological Society of South africa, Vol. 79, Part 3, 301-303.

Mangor, K., Bandeira, J.V., Dorst, K., Ewing, L., Fernando, C., Fröhle, P., Malherbe,

B., Mather, A.A., Mertens, T., Mocke, G., Pattiaratchi, C., Peters, K., Sigurdarson, S.,

Smith, D., Villarroel, D. and Wikramanayake, N. 2011. Mitigation of coastal erosion

along South Africanndy coasts New PIANC Guidelines for Countries in Transition (in

press).

Mather, A.A. 2006. Internal report on the erosion along Eastmoor Crescent, La Lucia

during September and October 2006. eThekwini Municipality.

Mather, A. A., 2007: Linear and non-linear sea level changes at Durban, South

Africa. South African Journal of Science, 103(11/12), 509–512.

Mather, A. A., G. G. Garland, and D. D. Stretch, 2009: Southern African sea levels:

corrections, influences and trends. African Journal of Marine Science, 31(2), 145-

156.

Mather, A.A. 2011. Sea level rise and its anticipated impacts along the east coast of

South Africa, In: Observations on Environmental Change in South Africa (Book editor

Larry Zietsman ), SUN Press. ISBN 978-1-920338-24-4.

Mavume, A.F., Rydberg, L., Rouault, M. and Lutjeharms, R.E. 2009. Climatology and

Landfall of Tropical Cyclones in the South-West Indian Ocean. Western Inidain

Ocean Journal of Marine Science, Vol. 8, No. 1, 15-36.

Nobuhito Mori, N., Yasuda, T. Mase, H., Tom, T. and Oku, Y. 2010. Projection of

Extreme Wave Climate Change under Global Warming Hydrological Research

22

Letters, 4, 15-19.

Palmer, B.J., Van der Elst, R., Mackay, F., Mather, A.A., Smith, A.M., Bundy, S.C.,

Thackeray, Z., Leuci, R. and Parak, O. 2011. Preliminary coastal vulnerability

assessment for KwaZulu-Natal, South Africa. Journal of Coastal Research, Special

Issue 64,1390-1395.

PIANC (2008). Waterborne transport, ports and waterways: A review of climate

change drivers, impacts, responses and mitigation. Climate Change and Navigation.

EnviCom – Task Group 3. April 2008.

Rossouw, J and Rossouw, M., 1999. Re-evaluation of recommended design wave

methods. Proceedings of the 5th International Conference on Coastal and Port

Engineering in Developing Countries (COPEDEC), Cape Town, South Africa.

Rossouw, M. and Theron, A.K. 2009. Investigating The Potential Climate Change

Impacts On Maritime Operations Around The Southern African Coast. 28th Annual

Southern African Transport Conference. ISBN 978-1-920017-39-2

Smith A.M., Guastella L.A., Bundy S.C. and Mather A.A. 2007. Combined marine

storm and South Africanros spring high tide erosion events along the KwaZulu-Natal

coast in March 2007. S. Afr. J. Sci. 103, 274–276.

Smith, A.M., Mather, A.A., Bundy, S.C., Cooper, J.A.G., Guastella, L.A., Ramsay,

P.J. and Theron, A., 2010. Contrasting styles of swell-driven coastal erosion:

examples from KwaZulu-Natal, South Africa. Geological. Magazine., Cambridge

University Press 2010. doi:10.1017/S0016756810000361

Theron, A.K. 2007. Analysis of Potential Coastal Zone Climate Change Impacts and

Possible Response Options in the Southern African Region. Proceedings of the

IPCC-TGICA Workshop/Conference on Climate Change, Fiji.

Theron, A.K, and Rossouw, M., 2008. Analysis of Potential Coastal Zone Climate

Change Impacts and Possible Response Options in the Southern African Region.

23

CSIR conference, Pretoria, South Africa.

Researchspace.csir.co.za/dspace/bitstream/10204/2561/1/Theron_2008.pdf

Theron A.K., Diedericks G, Mahery, A and Rossouw, M. 2010. Potential impacts of

climate change on the coastal zone: how far from the sea should we be? South

African Risk and Vulnerability Atlas. Dep. Science & Technology. www.rvatlas.org.

ISBN 978-0-620-45659-3

Theron, AK. 2011. “Climate change, sea level rise and the southern African coastal

zone: a general revue of causes, consequences and possible responses.”In:

Observations on Environmental Change in South Africa (Book editor Larry

Zietsman). SUN Press. ISBN 978-1-920338-24-4.

Theron A.K., Rossouw, M., Barwell, L. and Mahery, A. 2011. “Adaptation Measures

& Coastal Protection Options in Response to Climate Change Impacts in the Coastal

Zone of the Southern WIO Region.” Conference on Climate Change Impacts,

Adaptation and Mitigation in the WIO region: Solutions to the Crisis; Grand Baie,

Mauritius. 21-23 March 2011.

Tinley, K.L. 1985. Coastal Dunes of South Africa. South African National Science

Programmes, Report no. 109, CSIR Pretoria.

Tol, R.S.J. 2004. The Double Trade-Off between Adaptation and Mitigation for Sea

Level Rise: An Application of FUND. FNU-48 (submitted), Research Unit

Sustainability and Global Change, Hamburg University and Centre for Marine and

Atmospheric Science.

UNCTAD. 2008. Maritime transport and the climate change challenge. Note by the

UNCTAD secretariat. United Nations Conference on Trade and Development.

TD/B.C.I/MEM.1.2, 9 December 2008.

Van Ballegooyen, R., Theron, A.K., Wainman, C., 2003. Final input to the Risk and

Vulnerability Assessment (RAVA) for the Western Cape (included in the final report

to the Provincial Government of the Western Cape).