Lower Orange River Research Articles

The Orange River avifauna: abundance, richness and comparisons

Like many other southern African rivers, the avifaunal richness and abundance of the Orange River, southern Africa's longest, remains virtually unknown. Given that the Orange River runs through hyper-arid regions in its lower reaches, its linear oasis effect and its role as a reservoir for Red Data bird species is likely but has not been quantified. Two surveys either side of the border town of Noordoewer, in the rainy and dry seasons of 1996 and 1997 deter-mined that species richness was higher in riverine habitat (71 species) than in the surrounding Nama Karoo (46 species) confirming the linear oasis effect. Surveys revealed five Namibian Red Data species. Peregrine Falcons, Falco peregrinus, and African Fish Eagles, Haliaeetus vocifer, were relatively common while the endangered Cape Eagle Owl, Bubo capensis, occurred sporadically. Among wetland Red Data bird species, Black Storks, Ciconia nigra, occurred in less disturbed areas, and White-backed Night Herons, Gorsachius leuconotus, were an unexpected species at this locality. The overall species richness of 103 birds and a density of riparian birds of 31 -3 4 birds/10 km, makes the lower Orange River avifauna similar to the Cunene River but tenfold less abundant than Namibia's other perennial rivers. Despite the low diversity, the arid habitats of the lower Orange River support greater diversity than more easterly regions when all current surveys of richness and abundance from Lesotho to the mouth on the Namib coast are combined. This east-west trend may be explained by the slower flow and warmer water of the lower Orange River but natural turbidity and regulation may explain the generally low diversity and abundance indices. Major rivers in southern Africa appear to have been over-looked as wetland habitats, and further avifaunal surveys of all of them are recommended.

The role of flowering plant species in the survival of blackflies (Diptera: Simuliidae) along the lower Orange River, South Africa

This study is an investigation of the role that plants play in the survival of adult blackflies by providing shelter and carbohydrate food. A detailed phenological study of the 29 most abundant plant species in the Augrabies Falls National Park showed that throughout the year the percentage of plant species flowering was remarkably constant. It is therefore unlikely that the availability of carbohydrates would limit adult Simulium survival at any time of the year. Blackflies were recorded feeding on the flowers of Pappea capensis. Acacia karroo, A. mellifera, Tamarix usneoides, Ziziphus mucronata, Scholia afra and Sisyndite spartea. An additional survey showed that another 64 plant species flowered throughout the year, and these can be regarded as potential carbohydrate sources. Blackflies were observed sheltering in dense shrubs and trees that provide protection against predation and harsh environmental conditions. This study suggests that vegetated drainage lines are the means by which adult blackflies survive dispersal away from the river. It is concluded that carbohydrate scarcity cannot be considered a limiting factor to adult blackfly survival along the lower Orange River.

A reconnaissance botanical survey of the Lower Orange River (Blouputs to Onseepkans) in the Northern Cape, South Africa

In the past, the alluvial floodplains of the Orange River were covered with riverine shrubland and woodland. However, there are indications that this has changed and that this vegetation and habitat has been influenced by a number of factors, namely: expansion of irrigated crop farming; grazing pressure; and upstream dam construction. A botanical assessment was carried out along the Orange River between Blouputs and Onseepkans, in the Northern Cape to determine the nature and extent of the changes to the riverine vegetation, as well as to investigate the distribution of Combretum erythrophyllum and Rhus lancea. Only two specimens of Combretum erythrophyllum were noted whereas no Rhus lancea specimens were noted. There are indications that both the expansion of irrigated crop farming and grazing pressure has affected the vegetation of the plain and riverine area along the Orange River. Downstream from the farm Raap-en-Skraap (2819DA Skuitdrif), the natural vegetation of the riverbanks and islands is being replaced by alien plant species.

WATER MARKET INSTITUTIONS: LESSONS FROM COLORADO

Important water issues in South Africa relate to equity, efficiency of use, quality (return flow pollution) and instream uses such as the environment. Farmers in South Africa pay water rates whether or not water is used and water is not volumetric priced. Water markets can attach an opportunity cost price and scarcity value to water. Opportunity cost pricing by the state has received no support in the international economic literature largely because of estimation problems. Water markets have started to emerge in the Lower Orange River and in the Fish and Sunday's rivers in the Eastern Cape in South Africa but there are two reasons why agricultural water markets do not release water in South Africa. The first reason is that the only water trades that have taken place in these rivers are between non-users of water and intensive users. It may take time before all sleeper rights (water not used) are activated which is also the case in Australia. Secondly, irrigation farmers in South Africa along the Orange and Sunday's rivers are permitted to irrigate a larger area if they adopt water saving technology such as drip irrigation. Although this water saving technologies will reduce water application per ha, the consumptive use of water per ha may not decrease and will increase if a larger area can be irrigated. Agricultural water markets are thus increasing the use of water and not promoting its conservation. It is thus recommended that transfers should be based on consumptive use if return flow is significant.

Three new species of <i>Zygophyllum</i>(Zygophyllaceae) from Namibia and Northern Cape, South Africa

Three new species of Zygophyllum L. from the lower Orange River area in Namibia and Northern Cape, South Africa are described, namely, Z applanatum Van Zyl, Z. hirticaule Van Zyl and Z pterocaule Van Zyl.

Tertiary-age diamondiferous fluid deposits of the lower Orange River valley, Southwest Africa

The Orange River, the principal conduit for transportation of diamonds from the southern African interior to the Atlantic coast, has within its lower valley two recognized suites of gravel terraces in which part of the passing diamond population has been trapped. Both suites lie on eroded bedrock and both are downstream thickening-and-fining coarse clastic wedges. The older and higher terrace suite, comprising the Arries Drift Gravel Formation, is early mid-Miocene in age (19-17 Ma) and is referred to locally as the Proto-Orange terrace. The lower and younger terrace suite, locally known as the Meso-Orange terrace, has not yet been dated but is considered to be Plio-Pleistocene in age. Middle to Late Proterozoic bedrock, underlying both suites of terrace deposits, was deeply eroded during the incision of the Orange River which began in Late Cretaceous times. The Proto-Orange terraces, richer in diamonds than the younger Mesozoic deposits, form low-grade but large-average, diamond-size, gem quality placers which are mainly discussed here. Diamonds are best concentrated in cobble-boulder basal gravels on or close to the rough bedrock contact in three main trapsite settings: scour pools hosting oversize (obstacle) clasts return grades of 10 to 40 carats per hundred ton (cpht); push bars, where the grades range from 10 to 55 cpht; and bedrock highs with their associated oversize clasts, yielding grades of 6 to 12 cpht, do not concentrate diamonds to the same extent as the two former trapsites, but occur over a wider area and thus potentially enrich a greater volume of gravel. The average diamond (stone) size in these three trapsites is also upgraded, ranging from 1.5 to 2.8 carats per stone (ct/stn). The key factors in concentrating diamonds at the bedrock-gravel interface are turbulence scale and intensity created by the rough boundary conditions and the presence of fixed bedrock sites of turbulence, which are stable enough to initiate and retain around them the slow and stable growth of gravel that hosts the concentrated diamonds. The upper, more mobile gravels have far lower concentrations of diamond than the basal gravels, with grades dropping to an average of 0.3 cpht and stone size decreasing to 1 to 1.3 ct/stn. Sites of higher concentration in the upper gravels of the Proto-terraces are bar platforms/riffles (1 to 3 cpht and average stone sizes of 1.1 to 1.3 ct/stn) and bar heads (0.7 to 1.5 cpht and average stone sizes of 1 to 1.3 ct/stn) while bar tails are practically barren. Although the vertical decline in diamond concentration may be attributed to a decrease in diamond supply during the aggradation of the Proto-Orange gravels, the younger, lower grade Mesozoic gravels also display a similar vertical profile. Hence, diamond concentration in the lower Orange River deposits is influenced positively by the occurrence and nature of the localized fixed bedrock trapsites. From an exploration point of view, these fixed trapsites are more difficult to locate, often requiring extensive drilling, whereas the areally extensive but low-grade upper gravels are relatively easy to delineate. During exploitation, the localized but higher grade fixed trapsites provide a reliable source of above average-sized diamonds in an otherwise low-grade.

Post-Gondwana drainage and the development of diamond placers in western South Africa

The post-Gondwana history of the major rivers in the western part of South Africa is important because these rivers were instrumental in the development of diamond placers along the west coast of southern Africa. The evolution of the drainage systems that developed after breakup of west Gondwana can be viewed in three time-slots: the middle to Late Cretaceous, the early to middle Cenozoic, and the late Cenozoic periods. During the middle to Late Cretaceous there were two main river systems draining the interior. The one in the south, also referred to as the Karoo River, had its source in the present upper Orange/Vaal drainage basin and its outlet was at the present Olifants River mouth. The second and more northerly system, also known as the Kalahari River, drained southern Botswana and Namibia and entered the Atlantic Ocean via the lower Orange River. Erosion dominated the period immediately after breakup of west Gondwana and most of the diamonds released during erosion of Cretaceous kimberlites in central South Africa were transported by the Karoo River to the coast. By early Cenozoic times, the lower Kalahari River had captured the upper part of the Karoo River and the broad configuration of the present Orange River network was established. This capture and northerly shift of the Orange River, on the newly exhumed pre-Karoo surface, was the result of an accelerated uplift of the southern and eastern subcontinental margins ca. 100 to 80 Ma. During the early and middle Cenozoic, the climate was arid to semiarid. This resulted in a substantial reduction in erosion rates and hence few diamonds were released from the primary bodies during that time. Late Cenozoic fluvial gravels, however, dated as either middle Miocene or Plio-Pleistocene, contain diamonds that were reworked out of older Tertiary fluvial deposits. Sediments at the base of the Koa Valley and in the upper terraces in the Sak Valley formed the Koa River, a major tributary of the Orange River during the Miocene, and drained most of the area previously occupied by the lower Karoo River. The Koa River thus reworked diamonds trapped in the Cretaceous Karoo River deposits or terraces. Younger sediments of the Carnarvon Leegte were never part of the Koa system. In fact, the Sak River captured the upper Koa River by late Pliocene times and the Plio-Pleistocene lower terraces in the Sak Valley and the paleo-Carnarvon Leegte joined as the paleo-Hartbees River--another major tributary of the Orange in the Plio-Pleistocene. Although climatic changes were the major controls that initiated the alluvial pulses during the Cenozoic, asymmetric uplift of the subcontinent was ultimately responsible for the northwesterly shift of the Orange River.

DISCRIMINANT ANALYSIS OF WATER TRADE AMONG IRRIGATION FARMERS IN THE LOWER ORANGE RIVER OF SOUTH AFRICA / DISKRIMINANT-ANALISE VAN WATERHANDEL ONDER-BESPROEIINGS-BOERE IN DIE BENEDE-ORANJERIVIER GEBIED VAN SUID-AFRIKA

This study found that a water market emerged within the Lower Orange River for river water rights. The market emergence is attributed to the scarcity of water in this region and the demonstrated demand by farmers for a change in the allocation of these rights. Transfers were facilitated by authorisation of the Department of Water Affairs and Forestry permitting transfers of water rights, and the enabling environment defined by the regional Water Affairs office. Improving water trade could be achieved by the delegation of authority to the regional Department of Water Affairs to approve transfers, extending support to market transfers of canal water, and ensuring that water extraction is closely monitored as river water use increases in future. A discriminant analysis indicated that water rights transferred from farmers with potential to irrigate wine grapes, raisin grapes, and field crops to farmers with potential to irrigate table grapes, representing the highest valued use of the water. Farmers stated that the proposed new Water Law created much uncertainty about their water rights, stifling water market activity, and that it will lead to underinvestment in irrigated agriculture. Overcoming such institutional and legal barriers for market performance will require that water use allocations be specified for reasonable periods, be inherently secure, and water trading be permitted through the relevant legislatures.

A review of the Namaqua gecko,Pachydactylus namaquensis(Reptilia: Gekkonidae) from southern Africa, with the description of two new species

An analysis of morphological and allozyme variation in the Namaqua gecko, Pachydactylus namaquensis from southern Africa is presented. Three separately evolving lineages, well defined by morphology and allozyme variation, are identified. The isolated southern population, occurring on the southern escarpment and Cape Fold Mountains surrounding the western Little Karoo, is named P. kladamderma sp. nov., and is characterized by a slit-like ear opening, low number of granules bordering the mental (3-6) and mental and adjacent infralabials (513), the frequent (79%) occurence of the supralabial entering the nostril, and its drab brown base colouration. A northern population, occurring in southern Namibia and the Richtersveld is named P. haackei sp. nov., and is characterized by its more rounded or squared ear opening; high number of granules bordering the mental and adjacent infralabials (11-19), the general exclusion of the supralabial from the nostril (only 3.7% entry), and brighter, lighter colouration. It is further differentiated from P. kladaroderma on the basis of fixed differences at 11 allozyme loci. Both new species differ from P. namaquensis, which is mainly restricted to Little Namaqualand, but is sympatric with P. haackei in the Lower Orange River region, by their more heterogenous dorsal scalation, smaller cloacal spurs, lack of spine-like tubercles on the lateral surfaces of the tail, and more fragile skin. The type locality of P. namaquensis is restricted to ‘the vicinity of Springbok, Little Namaqualand, Northern Cape Province, South Africa’.

Biological Patterns Through Time in Southern AfricaSkeletons of Contact: A Study of Protohistoric Burials From the Lower Orange River Valley, South Africa.Alan G. Morris

Biological Patterns Through Time in Southern Africa<i>Skeletons of Contact: A Study of Protohistoric Burials From the Lower Orange River Valley, South Africa.</i>Alan G. Morris

The Skeletons of Contact: A Study of Protohistoric Burials from the Lower Orange River Valley, South Africa

The Skeletons of Contact: A Study of Protohistoric Burials from the Lower Orange River Valley, South Africa

Time of emplacement and metamorphism of Late Precambrian mafic dykes associated with the Pan-African Gariep orogeny, Southern Africa: implications for the age of the Nama Group

The Gannakouriep mafic dyke swarm straddles the border between South Africaand Namibia in the lower Orange River region, and was intruded during crustal extension associated with the early phases of the Late Precambrian Gariepian orogeny. A RbSr internal isochronage of 717±11 Ma has been obtained from fresh unmetamorphosed gabbro that forms relict patches in the biggest dyke of the swarm. By inference, the maximum age for the Gariepian orogeny, which deformed and metamorphosed the dyke swarm along its western margin, and forms part of the Pan-African system of mobile belts, is constrained by these age data. A product of the Gariepian orogeny was the growth of metamorphic amphibole in the dykes, which had a profound influence on the KAr age patterns. Within the amphibole isograd, the dykes possess coherent patterns indicating growth of the metamorphic amphibole 542±4 Ma ago. Lower grade sectors of the dyke swarm characterised by chlorite-scricite assemblages have lower KAr ages indicative of open system behaviour, perhaps promoted by the lack of a K-bearing stabilising mineral such as amphibole. Amphibolitised Gannakouriep dykes are unconformably overlain by the Nama Group, and so it follows that this sedimentary sequence post dated Gariepian metamorphism at ∼540 Ma. A minimum age for the Nama Group is given by the intrusion of the Bremen Complex at 521±11 Ma , thereby constraining deposition and by inference the Precambrian-Cambrian boundary in southern Africa to between 540 and 520 Ma ago.

FISH POPULATIONS IN THE MIDDLE AND LOWER ORANGE RIVER, WITH SPECIAL REFERENCE TO THE EFFECTS OF STREAM REGULATION

SUMMARY The results of two surveys, in March 1982 and September 1983, on the distribution and status of freshwater fish in the highly regulated section of the Orange River, from the P.K. Le Roux Dam wall to the mouth of the Orange River in the Republic of South Africa are presented. Collections are reported for the first time from the restricted diamondiferous areas in the extreme lower section of the Orange River. The known range of twelve freshwater fish species in the system has been extended as far down as 1,5 km from the mouth. Special attention is given to the Red Data Book species, Barbus hospes which occurs and breeds throughout the lower Orange River. It is suggested that stream regulation has probably been beneficial for this small, riverine Barbus species in contrast to B. paludinosus and B. trimaculatus which prefer quieter well vegetated habitats.

The freshwater fishes of the middle and lower Orange river

The occurrence and distribution of freshwater fishes of the middle and lower Orange River in the Republic of South Africa is presented, based on a survey conducted in September 1980. Particular attention is paid to the Augrabies Falls region including the Augrabies Falls National Park. Comments on the distribution and conservation status of the fishes are given.

Total rock Rb [sbnd]Sr and U [sbnd]Th [sbnd]Pb isotopic study of Precambrian metavolcanic rocks in the lower Orange River region, southern Africa

Rubidium, Sr, U, Th and Pb concentrations and Sr and Pb isotope data are presented for a suite of Precambrian metavolcanic rocks cropping out in the lower Orange River region of southern Africa. Good agreement between total rock Rb-Sr, Th-Pb and Pb/Pb ages obtained indicates an extrusion age of 1996 ± 15Ma. The total rock U-Pb system was disturbed in recent times and ages obtained are unreliable. Parental magmas to the volcanic rocks and associated plutonic intrusives were probably derived from the upper mantle, which indicates that a major crust producing event may have taken place in the lower Orange River region during the mid-Proterozoic (2.0–1.7 Ga). Reworking of part of this older crust during a 1.2-1.0-Ga event to produce gneisses within the neighbouring Namaqua Province is supported by Sr isotopes. Initial Sr and Pb in the lavas was probably derived from a mantle source that experienced a previous history of slightly high Rb/Sr and U/Pb, relative to postulated bulk earth evolution. Enrichment in Rb/Sr for the subcratonic mantle under southern Africa was previously known, and the results of this study indicate a similar pattern for U/Pb.