*EQ equinoxes (2006), LNC lunar nodal cycle (2006), MS March swell (2007) and WE winter erosion (2007). By helping insurance companies calculate premiums more effectively and assess claims linked to damages caused by coastal erosion, DEA can generate $31 million per year in additional profits for the insurance sector. 4). Ten swells coincided with spring tides and six with neaps (Table 5). Storms (particularly hurricanes) are often cited as important drivers of coastal erosion (e.g. Reference Gratiot, Anthony, Gardel, Gaucherel, Proisy and Wells2008; Oost et al. This process is known as longshore drift. report 2008007, Marine Geosolutions (Pty) Ltd, 2008). These changes were linked to the long-term behavior of oceanographic variables such as wave climate and mean sea level. Thus a storm surge hydraulic head was established which gave rise to a strong return flow. Contribute Information Coastal Erosion is defined as the weathering of rocks, removal of beach or dune sediment as a result of wave action, tidal currents or drainage. In response to the beach erosion the eThekwini Municipality started pumping sediment as beach . Coir logs are made from coconut fiber and are large-diameter. Simple calculations suggest that a minimum of 1.5 106 m3 sediment may have been removed from the Salmon Bay coastline and deposited 350 m offshore at depths of at least 20 m CD. Figure 10. "displayNetworkTab": true, Lesser swells are focused by headlands and result in megarip development and activation of erosion hotspots. and They are great for protecting riverbanks and are also suitable for erosion control on slopes and shorelines. 2013. Table 6. data, 2008: http://researchspace.csir.co.za/dspace/bitstream/10204/2561/1/Theron_2008.pdf). 1) deepened from 18.3 to 25.0 m CD between December 2005 and February 2006 (Table 4). Tidal data were obtained directly from the Hydrographer SA Navy. Note the absence of a nearshore bar and suspended sediment in the nearshore surf zone on the right. 2013. However, seawalls stop the supply of sediment, which can cause erosion. 1). The report highlights three hotspot neighborhoods on the North Shore, Sunset beach, Lanikea and Mokulia. These differ from storms in that the waves tend to be larger, of longer period and are not always accompanied by a tidal surge. Learn more about the method and technical details in the Digital Earth Africa Docs. #Coast & Ocean Competency Area, CSIR, P.O. Shoreline Changes on the Natal coast: Mkomanzi River mouth to Tugela River mouth, Shoreline Changes on the Natal coast: Tugela river mouth to Cape St Lucia, Shoreline Changes on the Natal coast: Mtamvuna River mouth to the Mkomazi River mouth, Gemorphological variability among microtidal estuaries from the wave-dominated South African coast, Identifying storm impacts on an embayed, high-energy coastline: examples from western Ireland, The increasing intensity of the strongest tropical cyclones, Leaky valves in littoral sediment budgets: loss of nearshore sand to deep offshore zones via chutes in barrier-reef systems, southeast coast of Florida, USA, Factors controlling shelf sediment dispersal along the south-east African continental margin, Observations of sandbar evolution on a natural beach, Geomorphological impacts of Inanda on the Mgeni Estuary, north of Durban, South Africa, Bulletin of Engineering, Geology & Environment, Significant contribution of the 18.6 year tidal cycle to regional coastal changes, Longshore sediment transport at the Izotsha River mouth near Port Shepstone, Sediment Dynamics Division, Coastal Engineering and Hydraulics, National Research Institute for Oceanology Council for Scientific and Industrial Research, World Scientific Publishing Corporation and East Meets West Productions, Contrasting morphologic behaviour at embayed beaches in Southern Portugal, Linear and non-linear sea-level changes at Durban, South Africa, Geologic control in the nearshore: shore-oblique sandbars and shoreline erosional hotspots, Mid-Atlantic Bight, USA, Morphological Impacts of Extreme Storms on Sandy Beaches and Barriers, The 18.6 yr nodal cycle and its impact on tidal sedimentation, Southern Oscillation Influences on the Gold Coast's summer wave climate, Review of existing wave data, wave climate and design waves for South Africa and South West African (Namibian) coastal waters, Daily to interannual cross-shore sandbar migration: Observations from a multiple sandbar system, Wave Runup, Extreme Water Levels and the Erosion of Properties Backing Beaches, Sea-cliff erosion as a function of beach changes and extreme wave runup during the 19971998 El Nio, Annual variation in the net longshore sediment transport rate, Beach cut in relation to net offshore bar migration, Handbook of Beach and Shoreface Morphodynamics, Coastal Engineering 2002: Solving Coastal Conundrums (Volume 3), Proceedings International Conference on coastal Engineering, Sydney, Combined Marine Storm and Saros Springhigh Tide Erosion Event, March 1920, 2007: A Preliminary Assessment, Longshore sand waves at Southampton Beach, New York: observation and numerical simulation of their movement, Behavior of beach profiles during accretion and erosion dominated periods, Rip currents, mega-cusps, and eroding dunes, Proceedings of Symposium: Nature Conservation as a form of Land Use. Human activity, however, can throw the natural coastal system out of equilibrium, causing a deterioration of the coastline. 1). Green, Andrew Significant open ocean swells during the May to August (2007) Winter Erosion cycle. Garlick, G. Luke The highly exposed South African predominantly sandy coastline is going to be susceptible to increased erosion by wind, wave processes etc due to the expected increased storminess. The natural coastline recovered (at least 60 %) within a year. KZN has a high-energy coastline with coarse-grained, sandy reflective to intermediate beaches (Cooper, Reference Cooper1991a). Contrasting styles of swell-driven coastal erosion: School of Geological Sciences, University of KwaZulu-Natal, Durban 4001, South Africa, Coastal and Catchment Policy, Co-ordination and Management, eThekwini Municipality, P.O. 2). Beach rotation (see Short, Reference Short and Smith2002) is a feature of the headland-bound bays. Erosion and Adaptation Project in West Africa Coastal Area: Inception Workshop October 19-21, 2016 Lom, Togo The coastal areas of West Africa is home to 31% of the West African population and produces 56% of the sub region's GDP. Reference Bning, Dispert, Visbeck, Rintoul and Schwarzkopf2008), significant wave heights are also likely to increase. Mostovski, Mikhail B. Observations made before, during and after record dramatic coastal erosion (shoreline recession of up to 40 m and substantial property damage). On most of the KZN coast, dunes and a steep hinterland prevented inland penetration and consequently sediment could only be moved alongshore or offshore (Morton & Sallenger, Reference Morton and Sallenger2003), except at estuary barriers where overwash occurred. A long period of stability (no major storms in 20 years), together with ignorance and greed, contributed to construction in inappropriate locations as landowners presumed them to lie outside the active coastal zone. The coastal zone is subject to significant anthropogenic modifications and both coastal ecosystems and human populations are especially susceptible to the negative impacts of any changes, including natural geohazards (IGOS, 2006). The aim of this paper is to document the impacts of the 20062007 Erosion Event on the KZN coast of South Africa (Fig. It can also absorb the shock of heavy rainfall. Monitoring coastal erosion in Africa using Earth Observation Data, Coastal erosion is a natural phenomenon, further impacted by human factors. The largest swells of the 2007 summer season, Cumulative (200607) high-water mark changes compared to known long-term values (19378: Cooper, 1991. Smith, Alan Etienne, Samuel 2020 Digital Earth Africa. and Figure 7. When combined with the impacts of human development it has the potential to cause significant changes to the coastlines of Africa. These benefits are estimated to be worth as much as 28% of the GDP. As the African population is predicted to double in the next 30 years, reaching 2.5 billion people on the whole continent, the health and efficiency of near-shore regions is increasingly fundamental to sustain socio-economic practices within coastal zones. The July, 2007 image was captured prior to peak erosion; note the lack of surf bars. This volume is eight times the annual longshore drift (see Schoonees, Reference Schoonees2000). The most dramatic effects were associated with a large swell on the March equinox (18th20th), which had an 8.5 m significant shallow water wave height (Hs) and a maximum swell height of 14 m (Hmax) (M. Rossouw, CSIR, pers. Erosion associated with such events was confined to isolated sandy coastal stretches along the KwaZulu-Natal coastline (Richard's Bay, Salmon Bay, Eastmoor Crescent & Vetch's Beach, Submarine Bay and St Michaels-On-Sea; Fig. This simply means that we are losing much more soil than we gain. Richmond, Bruce Beaches with, and adjacent to, inappropriate sea defences, Beaches where the built environment is located too close to the high-water mark, and. Ballito rocky coastline following the March 07 swell event. Leuci, Rio Maintain and rehabilitate natural dune vegetation, this assists in stabilising the frontal dune which in turn will offer protection against storm surge and erosion. This underlies the importance of seaside settlements, especially considering that half of the 15 African megacities (with over 10 million habitants) expected to be developed in the continent by 2050 arise in near-shore areas. These locations are erosion hotspots (EHS), as described elsewhere (List, Farris & Sullivan, Reference List, Farris and Sullivan2003; McNinch, Reference McNinch2004), that respond readily to large wave events. Cooper, J. Andrew G. Box 320, Stellenbosch, 7599, South Africa, https://doi.org/10.1017/S0016756810000361, Reference Ruggiero, Komar, McDougal, Marra and Beach, Reference Sallenger, Krabill, Brock, Swift, Manizade and Stockdon, Reference Bromirski, Flick, Cayan and Graham, Reference Hemer, McInnes, Church, O'Grady and Hunter, Reference Smith, Guastella, Bundy and Mather, Reference Thornton, Humiston and Birkemeier, Reference Thornton, MacMahan and Sallenger, Reference Cooper, Jackson, Navas, McKenna and Malvarez, Reference Castelle, Le Corre and Tomlinson, Reference Guastella, Smith, Mather and Bundy, Reference Gratiot, Anthony, Gardel, Gaucherel, Proisy and Wells, Reference Oost, De Haas, Jensen, Van den Boogert and De Boer, Reference Bning, Dispert, Visbeck, Rintoul and Schwarzkopf, Extreme storms on the Pacific Northwest Coast during the 199798 El Nio and 199899 La Nia, Shoreface morphodynamics of a high-energy, steep and geologically constrained shoreline segment in Northern Ireland, The response of the Antarctic Circumpolar Current to recent climate change. In quantitative terms, the average predicted soil loss rate for South Africa is 12,6 tons/ha/year, while the average soil loss rate under annual cropland (grain crops) is 13 tons/ha/year, which is much higher than the natural soil formation rate of less than 5 tons/ha/year. Dunes commonly reach heights of 3060 m, and are often compound features, varying in age from Late Pleistocene to Holocene (Tinley, Reference Tinley1971). The largest swells of the 2007 summer season. comm.). Eastmoor Crescent, Durban: erosion from 1989 (top) and 2006 (bottom). and Three of these were associated with the equinoctial and lunar nodal cycle (LNC) peaks. Aside from native vegetation, soil erosion mats are also a common way to protect against erosion. Coastlines empowers decision makers to prioritise and evaluate the impacts of local and regional coastal management based on historical coastline change. The styles of erosion during the March 07 event and other 2007 swells were markedly different. Bundy, Simon C. The team validated the tool against reference coastlines generated from very high spatial resolution multi-spectral satellite images. Destruction of the coastal resources continues to worsen The rapid growth of the coastal urban centres in Kenya, Tanzania, Mozambique and South Africa, and the fast development of the coastal tourism sector, produce vast quantities of pollution from untreated domestic sewage, posing a threat to the near-shore habitats such as coral reefs. The contrasting styles of swell-driven coastal erosion between the March 07 and the Winter 07 erosion events may be explained in terms of water-level dynamics and geomorphology. Loureiro, Carlos Substrate also played a key role and damage was greatest where structures had been built on sand (Fig. What can and cannot be done to prevent future erosion? Leuci, Rio (Due to the sampling intervals, varying from years to decades, these figures for envelopes of mobility have to be considered as minimums.) Changes in sediment dynamics (coastal erosion and deposition for example. 2012. The financing approved today from the IDA Regional Integration Window provides additional resources for the West Africa Coastal Areas Management Program (WACA) to undertake . 1), underwent little or no erosion during the March 07 event. Coastal erosion protection in South Africa must take into account natural processes that occur in coastal areas. Erosion during 2006 was caused by the development of a megarip (see Short, Reference Short1999) which formed a cusp 60100 m wide. At Richards Bay the intensity of swell exceedance events has remained fairly constant, but there has been an overall increase in number of exceedances since 1979 (Guastella & Rossouw, Reference Guastella and Rossouw2009). 1) experienced severe erosion. The higher the blocking headland the greater the observed run-up (Fig. The focus area for the validation has been West Africa, particularly the seaside resort of Saly Portudal in Mbour-Senegal. As the rising swell limb was very steep, offshore sediment transport probably took place early in the March 07 swell event following a process of episodic net offshore bar migration (see Ruessink, Pape & Turner, 2008). June 4, 2011 - Three major North African cities - Alexandria, Casablanca and Tunis - face losses of more than $1 billion each, over the next two decades, as risks of natural disasters intensify with the onset of climate change. The final erosion episode occurred on 30th August when a swell (Ho = 3.2 m) coincided with a very high spring tide (2.3 m CD) (Table 5). In addition to these methods, river bank erosion protection projects have been used to alleviate poverty in parts of the Western Cape. During this time there were no large (> 3 m) swells (Fig. Figure 11. The KZN coast, as with many coasts around the world is showing a general eroding trend. Following this, a large swell (Ho = 3.3 m) struck on the September equinox (Table 6), but produced little notable erosion, even though it was comparable to, and in fact slightly higher than the 31st August 07 swell (the last major erosive event). Coastal hazards are currently a major concern for several reasons: . While large swell events commonly move sediment into the longshore drift via megarip-currents, severe events such as the March 07 swell move it from the nearshore zone onto the shelf. Table 2. Coastal East Africa encompasses a beautiful tapestry of land and seafrom mountains and grasslands to mangroves and fringing coral reefs. They can also help establish vegetation growth. In South Africa, the coastal environment provides important economic and social opportunities. Between the swells on the 30th August (Ho = 3.2 m) and the 26th September equinox (Ho = 3.3 m), no major swell occurred and the nearshore (surf) bars were able to reform, restricting further erosion. Another method of coastal erosion protection is to plant coir logs. 2012. Here a coastal zone called the Admiralty Reserve, which extends from the HWL inland for 47 m is present. The event coincided with an extreme high tide cycle of 18.6 years and produced waves of up to 8.5 m. As a result, the water level was 2.7 metres higher than the chart datum, resulting in the construction of multiple coastal defences and a multitude of flood walls. We describe the morphodynamics of a series of swell events with attention to water levels, wave heights and erosion patterns revealed by a combination of visual observations, in most cases, and field measurements (Fig. However, the actual life will vary based on the concrete mix and accelerated corrosion rates. 3; Table 3), which remained semi-stationary some 500700 km southeast of the KZN coastline, between the 18th and 20th March 2007. Minor EHS erosion was associated with these events, but against the backdrop of the March 07 erosion, mostly went unnoticed at the time. 1) and comprises a number of short topographically bound beaches bracketed by rocky headlands, associated with wave-cut platforms. During 20062007, the KwaZulu-Natal coast of South Africa was exposed to several large swell events (Ho > 3 m), near the peak of the lunar nodal cycle, causing shoreline recession. The soft coastline at Little Maritzburg Lane (Fig. By protecting coastal habitats, local governments can reduce the vulnerability of coastal areas to extreme weather conditions. Professional seawall companies will use the best products and create customized design plans to meet the needs of each individual project. These tools use satellite images to assess the state of the coastline. The Problem Today Currently, 40% of soil in Africa is degraded. and Reference Sallenger, Krabill, Brock, Swift, Manizade and Stockdon2002). 1) underwent coastal erosion, associated with coastal dune undermining, and the HWL retreated by up to 30 m. Shelf sediment at the Richards Bay dredge dump site, located at 20 m CD and 3 km from the coast, had built up to 11 m CD prior to this event (January, 2006 survey). A ground-breaking study shows the increasing environmental threat the three cities face, such as flooding, storm surges and coastal erosion. In areas of vegetated coastal dunes, run-up never exceeded 4.9 to 5.9 m CD, and was often less. and Hinterland penetration was generally low due to the steep nature of the coastline; however, seawater surged 2 km into the Richards Bay Harbour. The typical service life for seawalls is 50 years. Backstrom, Joni Reference Smith, Guastella, Bundy and Mather2007); wave run-up was surveyed at 4.910.9 m CD (Mather, Reference Mather2007). Swell data from the South African Data Centre for Oceanography, compiled from voluntary observation ships, for the area 2930 S and 3133 E, indicate that this coast is dominated (40 % of the year) by large amplitude southerly swells (Begg, Reference Begg1978; Rossouw, Reference Rossouw1984), mostly generated by eastward moving cold fronts with low pressure centres passing to the south of southern Africa. 2011. This was followed by two large swells (> 5 m) on the 11th and 23rd May, both of which occurred on neap tide (Table 5). 1). Dunes, beach, nearshore and inner-shelf sands were eroded. Swells associated with such storms generally approach from the south and southwest (Hydrographic Research Unit, 1968), but once on the shallower continental shelf (< 100 m deep) are refracted and make landfall from a more SSE direction. 37.7.1 Coastal Erosion, Coastal Flooding, Soil and Water Salinization Coastal erosion, which results in a shrinkage of the coastline, is estimated on average at between 0.5 and 2 m per year. The swell peaked early on 19th March; data from the Richards Bay (Fig. Data from the March (2007) swell, measured at Durban. 2012. and Beaches with a thin veneer of sand over rock. Multibeam image of the Richards Bay offshore dredge dump site showing scouring and deposition. Ballito: multi-storey block founded on the dune cordon and located within the 5 m amsl contour. Green, Andrew Fortunately, there is a way to protect rivers from erosion and reduce the effects of floods. Besides flooding (a process of submerging of land that is usual dry by overflowing water), coastal communities must battle with other climate change induced challenges such as sea level rise, coastal erosion, ocean pollution, rising sea surface temperature, coral bleaching and severe droughts (IPCC, 2019 ). Green, Andrew Besides helping to keep the water clean, these features also play a crucial role in indirect economic benefits. Although the KZN coastline appears to have re-equilibrated, the sand loss in some urbanized coasts has resulted in the new HWL being 5 to 10 m landward of the pre-March 07 position. Coastal erosion is part of the natural coastal systems whereby coasts adjust to sediment availability and the ambient wave and tide conditions. Theron (Reference Theron2007) has calculated that 10 % stronger winds would give wave height increases of 26 %, with coastal sediment transport rates increasing by 40 % to 100 %. Reference Smith, Guastella, Bundy and Mather2007), meant that the wave sets were closely spaced and there was insufficient time between wave land-falls for water to drain away completely under gravity. The cost is $14 billion to stop coastal erosion, which is at a rate of losing 2.5 acres of land per hour. and Green, Andrew N. and unsubstantiated anecdotal information suggests that similar erosion occurred in the early 1940s. The higher run-ups were on the exposed Anstey's and Brighton beaches, whereas the more protected parts of the Durban Bight experienced lower run-ups. Winter 07 erosion was anomalously severe due to the lack of nearshore bars to dissipate wave energy; consequently, this energy reached the coast and strongly drove the megarip current cells driving the EHS localities. Explore the Digital Earth Africa Coastlines method andCoastal Erosion notebookon the Sandbox. For example, the March 2007 storm in Durban had maximum run-up levels of +10m above mean sea level (MSL) (Smith et al., 2007). From this point to the end of August, chronic coastal erosion occurred at some EHS localities: Little Maritzburg Lane (Ballito), Eastmoor Crescent, (Durban), Inyoni Rocks (Durban), Submarine Bay, Clansthal, Scottburgh and Mzumbe. Africas non-life insurance penetration rate is 1.8%, about half of the global average set at 3.3%. At Submarine Bay, comparable erosion was recorded in 1991 (R. Osborne, pers. At Ballito, shell middens, which were active until the 1920s (L. van Schalkweg, pers. Swell from ex-tropical cyclone Favio peaked four days before spring tides, while that from ex-tropical cyclone Gamede coincided with a spring-high tide (Table 2). Pristine coastal dunes which had been impacted, had re-vegetated to some degree and in some instances new fore-dunes had established. At Eastmoor Crescent, a similar scale of erosion to that of 20062007 was recorded in 1970 and 1989; both occurred near previous LNC peaks (Fig. 5). These indirect economic benefits are estimated at up to 28% of the GDP. Dramatic erosion took place on July 30th when a swell (Ho = 4.5 m), again coinciding with spring tides, struck the coast (Table 5). The local government was faced with a challenge concerning coastal defences when an extreme event in March 2007 devastated the KwaZulu-Natal coastline. In addition, it protects local biodiversity. The impacts of geohazards in coastal regions are typically considered to affect two priority areas, namely: coastal populations and ecosystems. Coastal areas have always played an important role in human activities and have grown in economic importance in recent decades. Figure 6. This is one reason why populations are concentrated along the coastline, with a rate of urbanization slightly . This will also increase the delivery of other ecosystem services. Nearshore bars had been destroyed or the sand moved too far offshore by the return bottom current to be effective (see Backstrom, Jackson & Cooper, Reference Backstrom, Jackson and Cooper2009). Ferreira, scar A subsequent survey (July, 2007) noted that this feature had been lowered to 14 m. Although this survey may include effects from subsequent swells (Fig. It typically occurs due to a combination of the energy produced by waves, wind and ocean currents. At 650 to 800 m off the southern exposed beaches, seaward of a very high point near Isipingo (Fig. It also reduces the wave energy that reaches the coast. In this context, coastal erosion on four urban beaches on Valparaso Bay was analyzed on a decadal scale. Ballito: headland induced erosion (with anthropogenic component), note the greater erosion on the southern side (left of image). At the same time, coastal zones are increasingly exposed to flooding that can result in significant damage. s protected, and restored and that sustainable use is promoted in order to halt degradation and biodiversity loss. How can we learn more about these coasts and provide policy and decision makers with the tools to better combat future threats and erosion for a sustainable management of coastal areas? This was due to a rocky point (surfer's point) to the south bypassing much of the wave energy northwards and focusing it on the soft coastline at the end of the rocky point. At its peak, winter erosion occurred during neap tides and even during low swells; however, the greatest impact was during high swells and spring tides. There is some evidence that EHS activity is episodic on the KwaZulu-Natal coast. The March 07 swell caused the HWL to retreat by 5 to 50 m. Dunes were undercut and structures erected on them were damaged. Coastal erosion events are driven by storm events and sea-level, amongst other factors. While this is often portrayed in a negative light, particularly when properties and infrastructure are threatened or damaged. Most of the beaches are backed by steep coastal dunes, although some are backed by rock outcrop. Bundy, S.C. Garland, Gerald Coastal erosion is a natural phenomenon. This amount of erosion is equivalent to the Richards Bay annual longshore drift volume (see Schoonees, Reference Schoonees2000). 2012. When combined with the impacts of human development it has the potential to cause significant changes to the coastlines of Africa. Most of the world's coastlines are eroding, and typical erosion rates for soft coastlines vary from 0.3 m to 1.0 m per year (Pilkey & Cooper, Reference Pilkey and Cooper2004). Both these natural and human elements of coastal zones are vulnerable to disturbances associated with natural processes in conjunction with anthropogenic forcing. Submarine Bay* Winter erosion schedule. Onshore, Salmon Bay lost some dune buffer (HWL retreated 10 m) during the March 07 swell. Determination of coastal management lines will ensure that development does not occur too close to the high-water mark, thus preventing further interference with natural sand movement. Reference Smith, Guastella, Bundy and Mather2007). It is also ideal for urban environments. According to a draft DISAL economic value study, by mitigating coastal erosion risks in 3 key sectors, Digital Earth Africa could inject ~$460 million per year into Africas economy and change the lives of ~270 million people in three key sectors: Coastlines is the first of its kind for the African continent, allowing users to observe patterns in coastal change over extended periods by mapping historical data.
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