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  Kosi Bay
General information

 
Land uses
Ecology
Topography and geology
Hydrology and geohydrology
Climate
Threats
References
Useful links
Map

General information      Top

The greater part of the Kosi System is situated between 26° 50’S to 27° 11’S and between 32° 38’E to 32° 53’E and it is stretches from an east north-easterly to a south south-westerly direction.  The system lies on the coastal plain west of the Lebombo Mountains in the northeastern extremity of the Ingwavuma (also known as Tongaland or Maputaland) district.  A small part of the catchment is situated in Mozambique (Ref. 1).

The Kosi system is approximately 470km north east of Durban (Ref. 1). The nearest town is Ingwavuma, situated 105 km from the estuary, although the village of KwaNgwanase is 13 km from the KwaZulu Department of Nature Conservation camp on the northwestern shores of Lake Nhlange (Ref. 16).

The system is composed of four interconnected, roughly circular lakes (Makhawulani, Mpungwini, Nhlange and aManzimnyama), a broad channel leading to an estuary, which opens to the Indian Ocean and three extensive areas of swamp. The lakes are separated from the ocean by a strip of forested sand dunes 600 - 2000 m in width (Ref. 16).  
The Kosi drainage area comprises approximately 500km2.  There are 2 main rivers that form the system, namely the Sihadhla River (± 30km), which rises in the Mtombeni pans.  This river receives water from 12 principal tributary systems.  It enters the Kosi system at Lake Amanzimnyama .  The other main river is the Nswamanzi River (± 15km), which collects water from 9 principal tributaries and enters Lake Nhlange on its western shore (Ref. 1).

The Kosi Bay System comprises16 different wetland types, including:

  • Shallow marine waters

  • Coral reefs

  • Sand/shingle shores

  • Estuarine waters

  • Tidal mudflats, including intertidal flats and saltflats

  • Salt marshes

  • Mangrove/tidal forest

  • Coastal brackish/saline lagoons

  • Coastal fresh lagoons

  • Deltas

  • Freshwater lakes: permanent

  • Freshwater lakes: seasonal/intermittent

  • Saline/brackish lakes/marches: permanent

  • Saline/brackish lakes/marches: seasonal/intermittent

  • Freshwater marches/pools: permanent

  • Freshwater marches/pools: seasonal/intermittent

Land uses        Top

Natural:  

The area was proclaimed as a nature reserve in 1987.  South Africa currently has 16 (by 2007 there will be a total of 19) wetlands designated as wetlands of international importance in accordance with the Ramsar Convention, one of which is the Kosi system. The site is a Nature Reserve administered by the KwaZulu Department of Nature Conservation. The surrounding area is rural KwaZulu and consists of communally owned land falling under the Tembe Community (Tribal) Authority (Ref. 16).
Agricultural:
In 1968 land cultivation comprised farming with sweet potatoes, maize, groundnuts, mangoes and cashews (Ref. 7).  The main problem with land cultivation in this area is afforestation (Ref. 8).
Industrial:
  At one stage, before the turn of the 20th century, Kosi Bay was considered to become a harbour, with Lake Nhlange the harbour and with the coastal dunes at Banga Neck being cut through to become an entrance (Ref. 8).
Urban:  
The nearest town is Ingwavuma, situated 105 km from the estuary, although the village of KwaNgwanase is 13 km from the KwaZulu Department of Nature Conservation camp on the northwestern shores of Lake Nhlange (Ref. 16).
Recreational:  
The area has special recreation potential and offers the possibilities of:

  • Walks through virtually undisturbed Coastal Dune forest and Swamp forest as well as open grassland and around the lakes. 

  • Fishing for optic-feeding game fish (marine) is probably the best in South Africa (except in the open ocean) as the system has a low turbidity. Main target species of sport anglers are the Kingfish (Caranx spp) Seapike (Spyraena sp) and Rock Salmon (Lutianus argentimaculatus). 

  • There is also the opportunity to observe the local people involved in their artisinal fishery using the traditional fish traps and spears. 

  • The atmosphere of the area is generally tranquil and the weather is conducive to pleasant camping throughout the year.

  • Bird watching in the bush and lakes is most rewarding although the species diversity is low relative to Ndumu Game Reserve.

Ecology     Top
Campbell described the Kosi estuary as “the most wonderful aquarium and gorgeous aviary” (Ref. 11).
Algae:  
 In September of 1977 blooms of the filamentous algae Enteromorpha were reported, particularly in the tidal basin.  The guide fences of the fish traps offered the most suitable substrate (Ref. 1). The most common plantonic algal species in the Kosi system, is Microcystis, especially abundant in the uKhalwe inlet (Ref. 3).
Vegetation:  
The most extensive report on the vegetation of the Kosi system is that by Tinley (Ref. 7).  The vegetation comprises:  

Swamp forests: The swamp forest community is the forest cover alongside streams, marshes and in certain places, the edges of the Kosi Lakes .  Dominant plants species of the Swamp forest are ferns (Ref. 10).

Marshes, sedge and aquatic communities:  Amongst the marshes and sedges, which surround the estuary, is Phragmites australis, Cladium and the fern Archostrichum aureum, as well as Scirpus littoralis, Cyperus papyrus and Juncus kraussi (Ref. 6).  

Mangal Communities:  Mangal communities are the littoral plant community below the high water mark, growing in waterlogged soils, such as the mangrove community (5 species) and the Barringtonia/Hibiscus association (Ref. 10).  

Coastal dune forests:  This is the plant community, which is under the most pressure.  The natives, who practice a “slash and burn” method of cultivation, leaving only destruction in their path, ruin it (Ref. 8).  

Grassland, open woodland and Palm communities:  Undulating grasslands occur on the west of the Kosi system, with the most dominant species being Urelytrum.  Amongst this occur patches of Palms, with the 2 most common species being the date palm ( Phoenix reclinata) and the Ilala palm (Hyphaene natalensis).  Woodland vegetation predominantly comprises species of Umdoni (Syzygium), Trichilia, Albizia and Dialium (Ref. 7).  

Aquatic vegetation:  
Terrestrial Vegetation: 
Invertebrates:  

In 1971, Hemens did a survey of the zooplankton in the tidal basin of the Kosi system and Lake Mpungwini , where the salinities varied between 12%° and   21%°. More than 50 taxa were found amongst the 3500 zooplankters obtained during a 50m haul.  However, this was considered a sparse representation of zooplankton and the sparseness was possibly due to the fact that the Kosi system is a nutrient poor system (Ref. 3).

In 1971, Champion recorded thirty species of benthos (bottom dwelling organisms) from the system.  Sparse populations on the anoxic bottom of Lakes Mpungwini and Makhawulani were confirmed.  Elsewhere, the benthic population was surprisingly diverse and numerically rich.  The sand prawn, Callianassa was found to be the most conspicuous in the tidal basin or lower reaches of the Kosi system.  The fact that the Kosi system is well known for its paucity of penaeid prawns, is indicative of the basic silt free nutrient deficient condition of the Kosi substrates (Ref. 15).  
A wide variety of insects inhabit the Kosi system, some of which are important elements of the benthos (Ref. 6).  Others, such as the weaver or tailor ant are common in the mangroves (Ref. 7), and from the collections pf Pennington in 1947/8; a particular species of butterfly (a skipper) is regarded as endemic to Kosi Bay .
Fish:   
There were several expeditions to Kosi Bay , all of which have published their fish species lists.  By 1978, the most recent investigation was that of Blaber (Ref. 14).  The Kosi estuary is considered to fulfil an important nursery function and it is said that “many thousands” of juvenile fish mature here before migrating to the sea.  The latest results in 1978, have shown that 133 species of fish occurred within the Kosi system, comprising 86 marine species, which were found in association with the reef at the mouth or penetrated the tidal basin, 39 species of resident estuarine fish, which penetrated the system to beyond the tidal basin and 9 freshwater species (Ref. 14).
Reptiles and Amphibians:  
Crocodiles were uncommon in the Kosi system in 1878 (Ref. 7) ad were restricted in the fresh water lakes Zilondo and Amanzimnyama.  Bruton (pers. comm.) reported all other species of reptiles and amphibians (Ref. 1).  Most notably of this list were the three species of semi-aquatic snakes.  Five species of turtles occur along the adjoining coastline, the most common species being the leatherback and loggerhead (Hughes, pers. comm., Ref.1).  The beaches of Tongaland are regarded as the only undisturbed nesting area for turtles in South Africa.
Birds:  

The birdlife of the Kosi system is essentially forest associated.  Of the ±247 bird species represented in the Kosi system, only ±85 species are water or estuary related.  Amongst the latter, are the rare Flufftail, White-backed Night Heron and the Crab Plover.

Mammals:  

The dominant mammal species in the Kosi system is the hippo, which increased in number from 19 (1958) to 31 (1978).  They are mainly concentrated in Lake Amanzimnyama in the south of the system.  Tinley (Ref. 7) and Bruton (Ref. 12) reported on the other 25 mammal species that occurred in the Kosi system in 1976.  Only the otter is estuary associated (Ref. 7).

Topography and geology      Top
Topography and Geography:  

The deepest area (northern trench) of Lake Nhlange is 31m.  There are varied opinions about the size of the Kosi system, with the size of the Lake Nhlange being estimated as between 30 and 37km2 in size (Ref. 4).  The Kosi system is a fine example of segmentation, a process whereby the system is transformed into circular water bodies, which are separated by low beach barriers (Ref. 2). 

Geology:

The Kosi system lies within the pale sandy soils of the Mozambique Coastal Plain, which overlie cretaceous beds.  The coastal dunes are composed of both Holocene and Pleistocene sand deposits (Ref. 2).  No rocks occur to the west of the coastal dunes, but on the coast, rock ledges, shelves and outcrops occur, one of which forms a small reef within the estuary upon which a very diverse fauna may be found (Ref. 5).

Orme is of opinion that the surface water area of the Kosi River system has deceased by 68% since the Holocene transgression, due to sedimentation, segmentation and reed swamp encroachment (Ref. 2).

Hemens et al said that Lake Amanzimnyama has decreased in depth since in has acted primarily as a sedimentation basin (Ref. 3).

The shallow entrance of the Kosi system is due to siltation, mainly because of substantial sand movement along the coast (Ref. 4).

Soils:  

Due to the high infiltration rate of water on the sandy coastal plain over which such rivers move, it is believed (Ref. 2) that only 5% of the total annual precipitation is borne by rivers/streams in the Kosi area.  The most sensitive area is apparently Lake Nhlange , which can be isolated with the slightest change in drainage patterns.

There is a fairly strong seasonal inflow of fresh water into the head of the estuary.  Up to 1976 there is very little information is available on the hydrology of the Kosi system.  Since 1976 the Department of Water Affairs installed 7 water gauges, which maintenance and monitoring were the responsibility of the KwaZulu Department of Nature conservation (Ref. 1).

The most memorable flood up to 1978, was caused by the Cyclone Claude, which swept over the Kosi system in January 1966.

  
Hydrology and geohydrology      Top

Climate      Top

The subtropical climate is warm to hot and humid (Ref. 16).  The prevailing wind directions are northeast and southwest in almost equal proportions. The calm and clean winter weather makes this coast one of the most attractive holiday resorts in South Africa .

Precipitation:    

Kosi Bay falls within a climatic region, which is one of the most well watered areas in South Africa . The average yearly rainfall at Kosi Bay is 980 mm. Rain occurs mainly during summer from October to March and the highlight of the rain season is from February to March. Sometimes heavy showers fall in short periods with consequent floods, which cause considerable damage. Although the rainfall is relatively reliable, droughts occur (Ref. 16).

Frost is virtually unknown, except occasionally in a few valleys in the interior (Ref. 16).

Temperature:  

Cloudy weather during the summer months reduce the sunshine duration to approximately 45 % while the percentage in winter is approximately 70. The average daily maximum temperature extends from 28oC in January to 22oC in July but extremes can reach 43oC and 34oC respectively. Average daily minima are 19oC in January and 9oC in July while extremes can fall to 7oC and -1oC (Ref. 16). 

Threats      Top

1.  Slash-and-burn

The local people destroy the swamp forest by the "slash-and-burn" method of cultivation.  This method is not only wasteful and destructive, but also unrewarding, because the sandy soils which the locals cultivate are unproductive. In places the destruction of the natural forests has come down to the water's edge, and on steep slopes this is leading to serious erosion.

Cultivating the swamps for crops like bananas often leads to canalization and drying out of the swamps. This leads to the oxidization of the peaty soils and the loss of the organic material, which renders the soil infertile, destroys its ability to hold water and stops the peat making process.

2.  Afforestation

Large areas of the catchment, outside the reserve, are being put under Eucalyptus plantations, threatening the wetlands and thus also the freshwater supply to the lakes system.  Sustained decrease in the freshwater inflow could result in a progressive rise in salinity in the lakes and a concomitant change in the ecological processes there.

3.  Chemicals

The increasing use of fertilizers and chemicals in the catchment can lead to eutrophication in future. Domestic sewerage has not been a problem yet, but can also contribute to eutrophication in future.

4.  Population pressure

Increasing (human) population pressure has the result of an ever-increasing demand for new land for cultivation and house building.

5.  Other

Schemes to develop a harbour in Kosi Bay , as were done at Richards Bay .

  • The in-filling by sediment of the lakes of the system, due to swamp forest destruction and load and other development.

  • The changing (permanent) of the current salinity regime by changes to the profiles of the channels.

  • Connecting the lakes and the ocean for boat traffic.

  • The encroachment of Phragmites reeds around the lakes and channels.

  • Noxious weeds - the principal one being Pereskia aculeate, which grows and fruits well in the area.

  • DDT pollution.

  • Gradual sanding up of the tidal basin. The fish traps used by the local community have often been perceived as contributing to the sanding-up of the tidal basin.

  • Bank erosion caused by the bow-waves from boats passing through the Mtando channel.

 

6.  Present threats

In the 19th century and again in 1981 plans were discussed to make Kosi Bay into a harbour such as was done at Richards Bay . This would have then given Swaziland better access to the ocean. These plans appear to have been shelved.

The dunes of the area are relatively rich in Titanium and other heavy metals and the mining of the dunes to retrieve these is always a possibility although there are currently no known plans.

References   Top
Ref 1:  Begg, G. (1978) The estuaries of Natal . L.Backhouse, Pietermaritzburg, pp. 24–41
Ref 2:  Orme, A.R. (1973) Barrier and lagoon systems along the Zululand coast, South Africa . In: COATES, D.R. ed.  Coastal geomorphology.  Binghamton , State University of New York : 181-217.  Technical report, Office of naval research (1).
Ref 3:  Hemens, J. et al. (1971) Natal coast estuaries: Environmental surveys, 3: The Kosi Bay estuarine lakes.  CSIR/NIWR project, (6201/9728): 1-20
Ref 4:  Hill, B.J. (1969) The bathymetry and possible origin of Lakes Sibayi, Nhlange and Sifungwe in Zululand ( Natal ).  Transactions of the royal society of South Africa , 38(3):        205-216
Ref 5:  Broekhuysen, G.J. & Taylor, H. (1959).  The ecology of South African estuaries, 8: Kosi Bay estuary system.  Annals of the South African Museum 44:279-296
Ref 6:  Boltt, R. E. & Allanson, B.R. (1975).  The benthos of some Southern African lakes, III: The benthic fauna of Lake Nhlange , KwaZulu , South Africa .  Transactions of the royal society of South Africa , 41(3): 421-262
Ref 7:  Tinley, K.L. (1978).  The ecology of Tongaland, 3: Kosi Lake system. Durban . Wildlife society of Southern Africa ( Natal branch): 69-140
Ref 8: Wager, V.A. (1972). Kosi Bay . African wildlife, 26(2): 81-86.
Ref 9: MacNae, W. (1968).  A general account of the fauna and flora of mangrove swamps and forests in the Indo-West Pacific region.  Advances in marine biology, 6: 73-270
Ref 10:  Vahrmeijer, J. (1966).  Notes on the vegetation of northern Zululand .  African wildlife, 20(2): 151-161
Ref 11:  Campbell , G.G. (1948).  Two expeditions to Tongaland.  African wildlife, 2(3): 53-56
Ref 12:  Bruton, M.N. (1978). Recent mammal records from eastern Tongaland in KwaZulu, with notes on Hippopotamus in Lake Sibaya .  Lammergeyer, 24: 19-27
Ref 13:  Campbell , G.G. (1969).  A review of scientific investigations in the Tongaland area of northern Natal .  Transactions of the royal society of South Africa , 38(4): 305-316
Ref 14:  Blaber, S.J.M. (1978).  Fishes of the Kosi system.  Lammergeyer, (24): 28-41
Useful links      Top

1.         Internet:     Kosi Bay System - Designated 28 June 199 www.environment.gov.za/Branches/BioConservation/17Ramsar/kosi/kosi_ris.htm

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