The Clansthal Conservancy lies on the South Coast of KZN, between the Mhlongwana River in the north and the Mhlongwa River in the south. It extends from the sea to the edge of the e'Thekwini boundary in the west, which is the edge of the farmland. It is some 2 190 ha in extent and lies between latitude 30° 12' and 30° 16' S, and longitude 30° 44' and 30° 48' E.
The Malongwana River has a total catchment area of 1 630 ha of which 930 ha is within the Clansthal Conservancy. The larger Mhlongwa River rises beyond Dududu, has a catchment area of about 8 000 ha or 80 km2, of which only 1 280ha lies within the conservancy. The remaining 260ha mostly consists of five small streams which drain directly into the sea, and run through Clansthal village.
The Marine Protected Area (MPA) extends in a rectangle from the Ngane River (north of the Mkomasi River) to the Mzimayi River in the south and for five nautical miles (over nine kilometers) out to sea. This takes it practically to the edge of the continental shelf or 100m sea depth. The proposed sanctuary area is a smaller rectangle within the MPA.
Clansthal enjoys a mild sub-tropical maritime climate as it is warmed by the strong Mozambique current. It has a mean annual precipitation of 900 to 1 100 mm, 70% of which falls between October and March. Much of the summer rainfall is in the form of thunder storms. The mean annual screen temperature is 20° C, with a mean maximum of 24,9° C and a mean minimum of 15,2° C. Summer day temperatures seldom exceed 30° C but it can be very humid.
Winter night temperatures are practically frost free. Winds are predominantly either north-easterly or south-westerly. September and October are the windiest months and May usually has least wind. The cooler south-westerly winds are often associated with cold fronts which bring light rain. The annual mean evaporation from a Class A pan is 1 620 mm, and the mean daily sunshine is 6,5 hours, indicative of cloudy skies. The winter has more sunshine hours despite having shorter day lengths.
Clansthal's topography can be described as a steep young water-worn landscape. There are no less than 432 primary catchments or individual tributaries, making the average primary land units less than six hectares. On more gentle terrain, these are much larger. The average mid-slopes are about 18%, making mechanised farming very difficult and some cultivated slopes are as steep as 35%.
The steepest part of the conservancy is in the west, where tributaries of the Mhlongwa have incised deep steep-sided valleys. Also, one very steep wooded slope, over 40 m high, occurs on the south bank of the Mhlongwana estuary, and an attractive waterfall, about ten metres high, occurs on the same stream, nearly one kilometre inland from the N2 freeway. The gentlest land slopes occur in the north-west, on either side of the old main road, and right at the top of the Mhlongwana catchment. This area is a plateau which occurs at an altitude of over 170 m.
East of the N2 freeway there are a few hills over 100 m and Greenpoint Lighthouse (Built in 1905) is at an altitude of 75 m. Directly opposite Greenpoint, the Aliwal Shoal lies less than three kilometres off shore and about five kilometres from the launch site at Umkomaas. The course of both rivers is very tortuous like all other rivers in KZN, which is a reminder that they once meandered their way slowly across a flat low lying plain about 30 million years ago and known as the 'old African land surface'. The closest remnant of this surface now occurs on Natal Group Sandstone (NGS), on the high lying plateau at Dududu (The Pines, > 400 m), near the headwaters of the Mhlongwa River. There is also an example of this surface in the north east of Vernon Crookes Nature Reserve.
The lower reaches of both rivers have very gentle gradients, so flat water in the Mhlongwana estuary stretches nearly to the N2 freeway and in the Mhlongwa, it stretches well beyond the N2. There is low lying alluvial land below five meters altitude adjacent to both rivers but it is far more extensive near the Mhlongwa.
In 1959, Dr B E Beater published maps of the soil parent materials on 198 South Coast cane farms. Prior to this Mr. L du Toit had mapped the geology of Natal, largely from horseback. Beater's original field by field survey was at a scale of 1 in 6000, and produced at the rate of about three farms a day. For publication he reduced this to a scale of an inch to the mile. It has subsequently been redrawn at a scale of 1 in 50,000. This map has been used to calculate the following approximate summary of parent materials occurring in the Clansthal Conservancy:
Dwyka tillite 1 260 ha 51%, Natal group sandstone (NGS) 450 ha 18%, Recent grey sands 320 ha 13%, Recent red sands 250 ha 10%, Recent alluvium 100 ha 4%, Intrusive dolerite 70 ha 3%, Pietermaritzburg shale 20 ha 1%
Dwyka tillite is by far the most abundant parent material in Clansthal. It consists of sediments laid down by receding glaciers, which left behind fine-grained glacial moraine or mud with rock fragments from the NGS and most of the older rocks embedded in it. It is about 350 million years old and is up to 350 m thick.
Excellent examples of this rock type outcrop on the beach at Errol Hayes rocks, north of Clansthal siding. Large and small fragments of NGS, Tugela schist, various colours of granite, amphibolite and pre-granitic quartzite can be seen embedded in a hard, fine grained, dark coloured matrix. The rock on the beach is heavily jointed due to temperature changes, and minor tension fractures can also be observed as gullies of deeper water in the surf.
Dwyka tillite weathers to form shallow, grey and dark grey, fine sandy clay loams and fine sandy clays of the Glenrosa, Westleigh, Longlands, and Oakleaf forms. On foot slopes and on bottom land, Kroonstad and Katspruit soil forms are found. All these soils have a slow steady intake rate and high rates of runoff, hence the deeply incised valleys. Geologists tell us that most of the residual soils on the KZN coast have been formed since the last major ice age, and are therefore less than 14 000 years old, or rather immature. Soils in the deep river valleys are even younger. Much older soils occur on the old African land surface.
NGS is a hard sedimentary rock 450 to 600 million years old, which weathers very slowly giving rise to gently sloping plateau, and mostly medium grained, grey, sandy loam soils of the Cartref form and deeper well drained red and yellow sandy loams of the Hutton, Griffin, Clovelly and Oakleaf forms. NGS occurs on either side of the old main road, on the farms Crosby and Roseneath, at altitudes of 170 to 215 m, near the headwaters of the Mhlongwana. The sedimentary strata dip quite steeply in an easterly direction, meaning that younger sedimentary rocks which overlie it usually occur at lower altitudes.
Recent grey sands are lighter in colour either because the rusty ferric iron oxide surrounding the sand grains has been sand-blasted away in the wind, or it has been reduced to ferrous iron oxide (FeO) in bottom land situations. Grey sands are usually lighter in texture (less clay) than the red sands. They are deep infertile soils with excessive permeability. The Fernwood soil form is common.
Resent red sands are red because of the presence of hydrated ferric iron oxide (Fe2O3 . H2O). They give rise to deep well drained loamy sands and sandy loams of the Hutton, Oakleaf and Shepstone forms. One very common soil found all along the KZN coast is called the Hutton form Clansthal series (named after this area by Dr Beater). It is a deep, well drained, red, medium grained loamy sand with a high steady intake rate.
Recent Alluvium is even younger and the surface layer is only as old as the last flood. It occurs on the edge of the two estuaries below the five meter altitude. Stratified alluvial deposits known as the Dundee soil form are common as are the somewhat older Oakleaf form. Some of this land has been drained for sugarcane production.
Dolerite is about 135 million years old and is an intrusive basic igneous or volcanic rock, which occurs as sills or lenses, dykes and pipes over much of southern Africa. No rock types between this age and the 300 million year old PMB shale occur in Clansthal. Dolerite weathers to form red, deep, heavy clay soils in Clansthal, of the Shortlands and Swartland forms. They have a high water holding capacity, are fertile and relatively resistant to erosion, although they are also often rocky. The rounded black rocks outcropping at Greenpoint and at the mouth of the Mhlongwa are fine examples of dolerite.
After the catastrophic volcanic eruptions which produced all the dolerite and basalt, there followed long periods of quiescent erosion, interspersed with active periods of continental upliftment and geological faulting. The most recent active period occurred about two million years ago, when marine deposits were uplifted above sea level as the Recent Sands. These deposits occur all along the east coast of Africa from the Eastern Cape right up to Somalia. At first these sands were blown into dunes but they were soon colonised by vegetation and have subsequently been sculptured by water erosion.
Pietermaritzburg shale is a sedimentary rock that overlies the Dwyka tillite and is about 300 million years old and up to 600 m thick. It was formed largely from erosion on the Dwyka tillite surface, hence it always weathers to form dark heavy clay soils of the Glenrosa, Mispah, Mayo and Milkwood forms on the hillsides, with Katspruit and Rensburg forms in the bottom land. PMB shales outcrop on the beach, just north of Greenpoint. They are steeply dipping in a north easterly direction and older Dwyka tillite occurs still further north so there must either be a minor fault south of the car park or the intrusive dolerite at Greenpoint has carried rafts of the lighter PMB shale upwards.
We have eight main vegetation types in the Clansthal Conservancy area. These are comprised of:
Coastal dune forest and primary dune vegetation (The areas are not yet mapped so no calculations have yet been made). Two fine examples of coastal dune forest occur in the conservancy; one north of Clansthal village on Clive Henderson's land between the R102 and the beach, and the other south of Greenpoint, again between the R102 and the sea. There are also remnants of dune forest within the village. Near the sea the primary dune vegetation was badly damaged by waves in March 2007, but it is good to see that it is recovering well.
Carpobrotus dimidiatus (Dune Vygie), Ipomoea pes-caprae (Dune Morning Glory), Chrysanthemoides monilifera (Dune Daisy) and Sporobolis virginicus (the hardy Dune Kweek) are all coming back strongly. The first three have been planted in front of some of the new barrier walls on the sea front. The low woody vegetation pruned by the salt spray has been much slower to recover. Here Mimusops caffra (Coastal Red Milkwood), Carissa macrocarpa (Amatungulu) and Brachylaena discolour (Assegai wood) are some of the dominant species. Their low canopy has been flattened by the salt spray. Further inland where the forest is taller Strelitzia nicolai (Wild Banana) is dominant but there are a wide range of tree species. Unfortunately woody invasive species, particularly Chromolaena odorata (Triffid weed), Lantana camara and Ricinus communis (Caster-oil) are a huge problem.
Finningley forest This occurs inland from the R102 from Crocworld to Clansthal village, and on both sides of the road to Finningley Estate, on the seaward side of the N2 freeway. Alan and David Crookes have had these forests proclaimed as protected areas. The range of species is wider than in the dune forest and the trees are taller. There are some magnificent specimens of Albizia adianthifolia (Flat-crown) and Strelitzia nicolai is still very common. Unfortunately much of the inland area was damaged by wildfire in August 2005 and recovery has been slow.
Steep riverine forest These forests are well preserved along both the Mhlongwana and the Mhlongwa Rivers and their many tributaries. There are plans to create a formal Nature Reserve in the Malongwana valley, half of which will fall into the Mkhomazi Conservancy. There will also be a hiking trail in this area extending from the beach to the waterfall on Finningley Estate. The range of species is very diverse. Near the waters edge trees like Rauvolfia caffra (Quinine tree), Syzygium cordatum (Umdoni) and several Ficus species are dominant, while on the rocky slopes, particularly on the rain-shadow hot northerly aspects the presence of Euphorbia grandidens (Valley Bush Euphorbia) shows the amazing diversity.
Arable land (Sugarcane and tree crops, formerly coastal thorn and palm veld) Most of the former grassland has been developed to commercial sugarcane, Eucalyptus plantations or orchard crops, making the tall coastal grasslands with their rich diversity of grasses, sedges and wild flowers the most threatened vegetation type in the area. Some biodiversity remains in the remnants found on the forest margins, road verges and infield roads. However, natural grassland is a fire climax vegetation and even if this land is not used for commercial cropping, if fire is excluded the grassland is rapidly colonised by woody vegetation including many invasive species and will eventually develop into tall forest.
The original tall grass veld had clumps of fire resistant Phoenix reclinata (Wild Date Palm), thorny Acacia species and Ziziphus mucronata (Blinkblaar-wag-'n-bietjie) mostly growing on the ancient termite mounds (iziduli) and surrounded by heavily grazed grassland. Lightening strikes caused most veld fires, but people robbing beehives also started veld fires. Most sugarcane in this area is well farmed. Fertiliser and herbicides are so expensive that farmers cannot afford to misuse them, so these chemicals do not pose a major threat to our health, the streams and rivers, or the deep ground water. Recently, local farmers have decided not to burn most sugarcane at harvest, so the smoke and smuts from cane fires are no longer a hazard to motorists or a nuisance to householders.
If agricultural land is sold and developed for more housing, the new environmental laws insist that wet agricultural land is restored to natural wetland as housing is not allowed in this area, but it is equally important that a wide buffer of natural grassland be left between the wetland and the housing development. It is also imperative that this land be properly managed, by controlling invasive alien weeds and preventing the natural succession to forest. This can be done by periodically burning the grass at the right time, by mowing or by using grazing animals.
Wetland and swamp forest A formal definition of wetland includes all hydromorphic soils, riparian belts adjacent to watercourses, estuaries and all open water, up to a depth of six metres. Much of the wetland on the farms has been drained by building cambered beds or by laying perforated underground pipes. Under the present legislation, farmers are allowed to keep this land under production as wet agricultural land, provided it does not erode or deplete natural water supplies. This land is excluded from new housing developments, although there are several existing houses situated in wetland or swamp forest. In the Clansthal Conservancy, much natural wetland has been invaded by alien woody species. The flood plains of the Mhlongwa estuary have been invaded by Schinus terebinthifolius (Brazilian Pepper) and annual weeds like Xanthium spinosum (Spiny Cocklebur) are also a problem. Where wetland occurs adjacent to grassland or sugarcane, there are many grasses, sedges and rushes that dominate the vegetation, but where it occurs within a treed area, a swamp forest tends to develop. Here Rauvolfia caffra (Quinine tree) and Syzygium cordatum (Umdoni) tend to be the dominant species, but Hibiscus tilliaceus (Lagoon Hibiscus) forms a dense swamp forest on the edge of the estuaries.
Homesteads, farmyards and gardens There are about 150 houses in the village of Clansthal with about 20 more units under construction. Most are fairly large houses in big gardens. There are more houses at the lighthouse, Crocworld and on the farms. At Roseneath (also called Craigieburn?) in the north west of the Conservancy, there is a commercial village with a much larger population than that at Clansthal. The gardens in Clansthal are mostly dominated by large trees and sweeping lawns. Although the modern trend is to garden only with indigenous plants, there are many beautiful non-invasive exotics that would be a great pity to remove.
Roads, the railway and, the road and railway verges The N2 freeway bisects the conservancy down the middle, but the only on and off ramps are outside this area. The R102 runs through Clansthal village and the old main road runs through Roseneath in the north west corner. Close to the sea runs the electrified line of Durban Metro Rail, which operates a passenger service and carries agricultural lime and crushed marble from Port Shepstone for Natal Portland Cement (NPC). The railway line was sited near the sea because of the gentle gradients and the direct route but it passes through very valuable land. Clansthal siding (miss spelt by Metro Rail as 'Clausthal') is central to the village. Most streets are tarred and there are many dirt roads for field access and crop extraction on the farmland. The road and railway verges are predominantly tall grasses, which are slashed two or three times in summer. Hyparrhenia species (Thatching grasses) seem dominate on the road verges. Metro Rail also uses strong contact herbicides adjacent to the line so here annual grasses and broad-leafed weeds predominate. A category one alien weed, which has become naturalised along the South Coast railway line, is Cenchrus brownii (Burgrass). It is an annual with very sharp burrs which stick in wool and fur. It arrived in Durban about 1945 and was soon proclaimed a noxious weed.
Rocky and sandy beaches Technically all this including the surf, is part of the wetland, but it is sufficiently distinctive to merit separate classification. In addition it is public land and falls within the Marine Protected Area (MPA). In the north, at the mouth of the Mhlongwana estuary there is a sandy beach and the mouth remains closed for most of the year. Henderson's sandy beach stretches virtually undisturbed for about a kilometer south. Then there is more than a kilometer of extensive rocky shore and beach until Errol Hayes rocks near the northern end of Clansthal village. The sandy beach of Blamey Bay lies in front of most houses along Greenpoint Drive. It is now mostly flanked by barrier walls on the private land, but there are three foot paths, which have become public rights of way through the village and onto the beach. There is also the public parking area for about 20 vehicles. The southern end of Blamey Bay is again rocky, first with PMB shale and then with dolerite at Greenpoint. South of Greenpoint there is 2,5 km of undisturbed sandy beach, past Mamba Alley where there are more footpaths from the lay-bys along the R102, across the railway line, and down onto the beach. The most southerly part of the conservancy is at Black Rock at the mouth of the Mhlongwa estuary.