Our fix for the Richards Bay beach

IN this last of our series of five articles on beach erosion, we want to present a solution – something that can accept the power of the waves, reduce their velocity and absorb their forces.

Something little, formed by waves and wind and when stabilized by pioneers of the environment, can save our beloved beaches.

Some 80% of the KZN coast is dominated by sandy beaches, most of them located on the north coast.

Sand on the beaches originates primarily from inland erosion and is transported to beaches via our river systems.

Models predict that owing to sea-level rise, the northern region will have more coastal retreat than the other two regions.

This is owing to the north having many more dissipative beaches compared to the central and southern regions.

Dissipative beaches characteristically have fine sand that is easily eroded and shallow slopes. These two characteristics make them more vulnerable to erosion and inundation, and hence they display the greatest retreat.

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.

Also read: Coastal vegetation’s positive impact

In fact, in specific circumstances where the source or supply of sediment to a beach area is interrupted or largely reduced (the case at Alkantstrand), short-term erosion in the order of even 100m or more is possible in some areas (as evidenced by observations elsewhere).

Our serious erosion problems have originated as a result of man’s activities.

Along our shoreline there exists a net littoral sand drift in a northerly direction (the coast’s natural ability to repair itself).

When this drift is interrupted by a breakwater, groynes or other structures, accretion occurs on the up drift side (south) and erosion on the down drift side (north) of the structure.

This situation is clearly illustrated by recent Google Earth images of the Richards Bay harbour breakwater.

Our coast’s natural ability to repair itself is further compromised by the dysfunctional coastal dune cordon.

In KZN, the last 12 years have already seen a 22% increase in coastal urbanisation in the 100m strip inland of the high water mark.

Additionally, maps of the conservation status of vegetation types in KZN show a band of about 50km from the coast (excluding the northern third of the province) that has mostly been transformed from endangered to critically endangered in the last five years.

Population increase
We are not alone coastal zones have changed profoundly during the 20th century with increasing populations, economies and urbanisation.

Today, low-elevation coastal zones below 10m elevation contain about 10% of the world population.

In the 136 port cities around the world with more than one million inhabitants there is a total population of 400 million people, of which about 10% are exposed to a 1 in 100 year coastal flood event.

Indicative estimates suggest that about 200 million people and infrastructure worth five trillion dollars, are threatened today.

This exposure continues to grow at a rapid rate and risks are growing as sea levels rise.

Also read: Contributing factors driving beach erosion

Improved understanding of sea-level rise and variability is required to reduce the uncertainties associated with sea-level rise projections, and hence to contribute to more effective coastal planning, management and adaptation in the presence of the many pressures on coastal regions.

Appropriate adaptation in and along the Richards Bay coastline can significantly reduce the impact of this sea-level rise.

Planned adaptation can range from retreat from rising sea levels, through planning and zoning of vulnerable coastal regions such as at Alkantstrand, accommodation through modification of coastal infrastructure and the construction of facilities such as cyclone protection centers, to protection of our highly valued coastal strip.

Planned adaptation will be more cost effective and less disruptive than forced adaptation in response to the impacts of recent extreme events and needs to be undertaken in the context of the many pressures on the strip as a result of rapid coastal development.

Proposals for Richards Bay
A soft coastal system for Richards Bay beach needs ‘a soft engineering’ solution.

The optimum erosion buffer will be a natural dune cordon system. This should be established wherever additional protection is required.

The municipality and property owners should be encouraged to reestablish and rehabilitate the dune systems between their properties and the sea. Where such replication of the natural dune cordon is problematic, the use of soft engineered, artificial vegetated dunes such as the Dutch system, must be considered.

Should such a dune be created and vegetated (critical to its survival and use), proper access control via boardwalks erected over the dunes should be provide to protect the dune. Breaks between crests of adjacent dunes perpendicular to the shoreline should especially be avoided.

Perpendicular breaks are preferential pathways for wave run-up during storm surges, which lead to excessive erosion of the dunes.

These breaks should be slanted diagonally to the shoreline to minimise dune erosion. The dunes should also be planted with endemic coastal vegetation intermixed with a range of pioneer species and maintained until the vegetation is well established.

Installation of a modern sand pumping and bypass scheme facility (maintenance by nourishment) on the south side of the harbour breakwater will be the most economic proposition (Figure 1) – moving sediment from the south side with similar sand grading back to the north side.

The bypass will allow the littoral drift to recover with the additional sediment on the Alkantstrand beach essentially shifting the wave run-up further away from inland infrastructure, creating a buffer.

It is however important to note that to protect dunes from erosion, the dry beach has to be flat and wide enough to approximate to the Bruun-type profile at raised water level equilibrium (explained in earlier articles).

For this to work, as we have been interfering with nature, requires a more thorough knowledge of the coastal area, including natural beach fluctuations. This is essential and a study of the possible effects of the proposed works on the stability of the adjoining shorelines should be made.

A well maintained beach will provide a very effective shore protection.

Dredger spoil, which might also have assisted in replenishing the beach sand and curbing erosion on the northern beaches, has long-term pollution concerns owing to port and ship activities.

Ships entering and leaving the port produce waste (eg galley waste, residues and oily mixtures) for which there is limited options for disposal.

Dredger spoils could however potentially contribute to the establishment of a line of artificially created dunes at Alkantstrand.

In Durban the long-standing sediment supply problem (interruption of littoral drift due to harbor construction and dredging) was eventually solved by such a sand bypass scheme, completed in 1982.

Together with the bypass scheme new groynes, completed in 1985 and improved in 2003, were also added.

The sand bypass scheme consists of a concrete hopper and a series of booster stations 700m apart and connected with a 400mm diameter high-density polyethylene pipe.

The hoppers receive 5 000 m3 of fluidized sand. This sand is then be re-dredged by a fluidizing and pumping mechanism at the hopper station and then pumped to various outlets between Vetch’s and Bay of Plenty beach, totalling a length of 3.5km.

The groynes have also been worth the expense and effort, providing not only stable beaches, but a recreational attraction.

Once the sand supply to our beaches has been restored, let us accept the proposition that following nature is the way forward.

With nature we can confront our beach erosion. Let us also use the two barriers that the Netherlands have successfully used against the violent sea for hundreds of years, the one natural – the dune – and the other a human surrogate – the dike.

Can this insignificant ‘dune’ providing the defense of their whole country, also become the defense of our beach?

• Jean Simonis is a professor in the hydrology department at the University of Zululand

References
a) Celliers, L and Ntombela, C. WIO-Urbanisation, Coastal Development and Vulnerability and Catchments.
b) Corbella, S., Stretch, DD., 2012. Coastal defenses on the KwaZulu-Natal coast of South Africa: a review with particular reference to geotextiles; Journal of the South African Institution of Civil Engineering Vol. 54 No 2, October 2012, Pages 55–64, Paper 810.
c) Environmental Management Framework for the Richards Bay Port Expansion Area and Industrial Development Zone: 5.5 ZONE 3: PORT ESTUARY, MARINE AND SEASHORE AREA
d) Harris, LR., 3008. The Ecological Implications of Sea-Level Rise and Storms for Sandy Beaches in Kwazulu-Natal, MSc, December 2008, UKZN.
e) Mather, A and Theron, A. 2012. Recent Extreme Events along the Coast of South Africa, 2012 Draft.
f) McHarg, IL., 1992. Design with nature, John Wiley & Sons, NY.
g) Palmer, B., Van der Elst, R., Parak, O., 2011. Understanding our Coast: A synopsis of KZN’s coastal zone. KwaZulu-Natal Department of Agriculture, Environmental Affairs and Rural Development, Cedara, Pietermaritzburg. 32 pp.
h) Pauselli, M., 2010. Promenade Protection: Country Club Beach to Blue Lagoon Beach. GAP Consulting.
i) Smith, A., Guastella, LA., Mather, AA., Bundy, SC., Haigh, ID., 2013. KwaZulu-Natal coastal erosion events of 2006/2007 and 2011: A predictive tool? South African Journal of Science; Vol. 109, No. ¾ , March/April 2013.
j) UNESCO, 2010. Sea-level Rise and Variability. A summary for policy makers: Intergovernmental Oceanographic Commission.
k) Zwamborn, JA., 1970. Coastal Erosion and Beach Restoration Measures: Die Siviele Ingenieur in Suld-Afrika – November 1970.

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