The geomorphic provinces of South Africa, Lesotho and Swaziland: A physiographic subdivision for earth and environmental scientists

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  • This article was downloaded by: [Fondren Library, Rice University ]On: 25 October 2014, At: 12:46Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK

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    The geomorphic provinces of South Africa, Lesothoand Swaziland: A physiographic subdivision for earthand environmental scientistsT.C. Partridge a , E.S.J Dollar b , J. Moolman c & L.H. Dollar ba Climatology Research Group , University of the Witwatersrand , WITS, 2050, SouthAfricab CSIR , Natural Resources and Environment , P.O. Box 320, Stellenbosch, 7599, SouthAfricac Directorate: Resource Quality Services, Department of Water Affairs and Forestry ,Private Bag X313, Pretoria, 0001, South AfricaPublished online: 23 Mar 2010.

    To cite this article: T.C. Partridge , E.S.J Dollar , J. Moolman & L.H. Dollar (2010) The geomorphic provinces of SouthAfrica, Lesotho and Swaziland: A physiographic subdivision for earth and environmental scientists, Transactions of theRoyal Society of South Africa, 65:1, 1-47, DOI: 10.1080/00359191003652033

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  • The geomorphic provinces of South Africa, Lesothoand Swaziland: A physiographic subdivision for

    earth and environmental scientists

    T.C. Partridge FRSSAf1, E.S.J Dollar2*, J. Moolman3 & L.H. Dollar2

    1Climatology Research Group, University of the Witwatersrand, WITS, 2050 South Africa2CSIR, Natural Resources and Environment, P.O. Box 320, Stellenbosch, 7599 South Africa

    *Author for correspondence: Present address MWH Global UK, Chepping House,1718 Temple End, High Wycombe, HP13 5DR, UK

    e-mail: evan.dollar@mwhglobal.com3Directorate: Resource Quality Services, Department of Water Affairs and Forestry,

    Private Bag X313, Pretoria, 0001 South Africa

    This work has drawn upon previous attempts to define geomorphic provinces, but also on more recentwork on the geological and geomorphological evolution of southern African fluvial systems. It has alsoused Digital Terrain Model (DTM)-derived data and statistical techniques to determine 34 geomorphicprovinces and 12 sub-provinces within South Africa, Lesotho and Swaziland. Ninety-nine main stem riverlongitudinal profiles and valley cross-sectional profiles were generated from the DTM-derived data, and astatistical technique, the Worsley likelihood ratio test (WLRT), was applied to define statistically signifi-cant changes in slope and valley cross-sectional width along the river continuum. This isolated 471macro-reaches for the 99 main stem rivers. Each macro-reach was then analysed using a variety ofdescriptors including shape, best fit curve, slope, sediment storage potential and valley width. Principalcomponent analysis was applied to the data set to determine whether significant groupings existed,indicating significant similarities in the data by way of area, and conversely, whether distinct differencesbetween groups of data were evident. The scores for the whole data set showed a large grouping around theorigin with some scatter along the PC1 axis. Distinct groups were, however, evident for macro-reacheswithin each province. These reflect the extent of uniformity in the slopes, valley widths, altitudes andshape descriptors of each province. A description of each of the 34 provinces and 12 sub-provinces ispresented.

    Keywords: geomorphic provinces, South Africa, Lesotho, Swaziland, conservation planning, rivers.

    INTRODUCTIONOn a global scale, freshwater ecosystems are experiencing a

    significant loss of biodiversity due to human impact (Klaphakeet al., 2001). There is a growing recognition that this loss is notsustainable in the long-term because functioning aquatic eco-systems deliver significant economic and social benefits to soci-ety (Costanza et al., 1997). Progressive legislation has beenpromulgated in some countries to ensure that freshwater eco-systems are protected [e.g., South African National Environ-mental Management: Biodiversity Act (No. 10 of 2004)], andthat a balance is achieved between using freshwater as a re-source (rivers and other surface and groundwater bodies) andprotecting it [e.g., the South African National Water Act (No. 36of 1998)]. In addition to nation-state initiatives, there are nu-merous international conventions that seek to conserveaquatic ecosystem diversity [e.g., Convention on BiologicalDiversity (CBD), Ramsar Convention].

    One of the main objectives in protecting freshwater ecosys-tems is to ensure the long-term survival of native species andcommunity types through the design and conservation of port-folios of landscape-scale spatial units (cf. Groves et al., 2000).The identification and selection of representative spatial units

    that conserve the diversity of communities and ecological sys-tems represents a significant challenge and various solutionshave been offered [e.g., Omernik, 1987; Roux et al., 2002;Kleynhans et al., 2005). Conventional wisdom has it that a port-folio of representative spatial units/sites is needed to help setconservation targets and goals (Nel et al., 2007). The targets areset at multiple spatial scales and levels of organisation to ensurethe protection of all communities and ecosystems and not justthe rare ones.

    South African contextIn 2002 the then South African National Department of Water

    Affairs and Forestry (DWAF), the Council for Scientific andIndustrial Research (CSIR) and the Water Research Commis-sion (WRC) embarked on a project to develop a policy andplanning tool(s) for the systematic conservation planning offreshwater ecosystem biodiversity in South Africa (Nel et al.,2005). Although a number of objectives were identified for thisproject, termed the Freshwater Biodiversity Initiative (FBI),two are relevant here: to identify those freshwater ecosystems best suited to receiv-

    ing a high protection status; and

    Transactions of the Royal Society of South AfricaVol. 65(1), February 2010, 147

    ISSN 0035-919X print 2010 Royal Society of South AfricaDOI: 10.1080/00359191003652033http://www.informaworld.com

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  • to develop methods and data layers for the spatial represen-tation of both biodiversity pattern (so that a sample of allbiodiversity can be conserved) and ecosystem processes (sothat the processes that sustain biodiversity can be sustained).This needs to be done at scales that are appropriate tonational and sub-national biodiversity planning initiatives.To meet the second objective, an approach was developed

    that incorporated the notion of physical signatures as surro-gates for biodiversity pattern. Although the concept of catch-ment signatures had been developed by King & Shael (2001),the concept of physical signatures for rivers was first applied aspart of the Greater Addo Elephant National Park Conservation(GAENP) project (Roux et al., 2002). The aim of the GAENPproject was to conserve biodiversity and stimulate sustainabledevelopment in the region. This required the identification ofoptions for expansion that would allow for the conservation ofrepresentative and viable biodiversity patterns and processeswithin the context of systematic conservation planning (cf.Margules & Pressey, 2000). As the biological information withinthe GAENP was limited, the study focussed largely on physicaltemplates of the ecosystems. This involved delineatingbiodiversity patterns for rivers and streams using physical sur-rogates (e.g., geology, climate) and identifying the ecosystemprocesses that maintained biodiversity. Roux et al. (2002) madethe point, as did Stanford (1998), that physical characteristics,such as geology and climate, control the biological attributes ofrivers and streams. Roux et al. (2002) went on to argue thatstream biota can be considered to be protected by conservinghabitat heterogeneity or pattern. This approach was used forthe GAENP study to construct signatures of physical patternwith some success. Roux et al., (2002) concluded that there wasconsiderable scope for further development of physical signa-tures as surrogates for biodiversity in freshwater ecosystems.

    The concept of physical signatures has recently been furtherdeveloped for South African rivers; these advances aredescribed in a companion paper (Dollar et al., 2010). This articleexplains that the development of physical signatures is based

    on a theoretical framework for interdisciplinary understand-ing of rivers as ecosystems (Dollar et al., 2007). Application ofthis framework requires, among other dimensions, a detaileddescription of the relevant levels of organisation that character-ise different subsystem hierarchies (e.g., geomorphology,hydrology and ecology) of the river ecosystem. The highestlevel of organisation of the geomorphology hierarchy is repre-sented by a geomorphic province (Figure 1). Geomorphic prov-inces are defined as similar land areas containing a limitedrange of recurring landforms that reflect comparable erosion,climatic and tectonic influences, and impose broad constraintson lower levels of organisation, e.g., drainage basins, macro-reaches, channel types (Figure 1) (Dollar et al., 2007).

    This article describes the process of revising the geomorphicprovinces delineated by Lester C. King (1967) for South Africa,Lesotho and Swaziland, and presents a revised description ofeach of the provinces. These geomorphic provinces have beenutilised in developing physical signatures for southern Africanrivers (see Dollar et al., 2010) for the purposes of systematic con-servation planning.

    GEOMORPHIC PROVINCESLester C. King delineated 26 geomorphic provinces for south-

    ern Africa in 1942 (King, 1942). These were later rationalised to16 in 1951 (King, 1951) and finally to 18 in 1967 (King, 1967).Kings provinces incorporated work by Gevers (1942), Taljaard(1945), Wellington (1944; 1955) and Cole (1966). King (1967)described geomorphic provinces as regions of relatively uni-form physiography that were more or less unique, althoughsometimes grading into one another. They were based on ahierarchy of criteria that included:1. Geomorphic history.2. Geological structure.3. Climate.4. Location.5. Altitude.

    Geomorphic provinces have been described elsewhere. In

    2 Transactions of the Royal Society of South Africa Vol. 65(1): 147, 2010

    Figure 1. Hierarchical descriptions of levels of organisation (after Dollar et al. 2007).

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  • Partridge et al.: The geomorphic provinces of South Africa, Lesotho and Swaziland 3

    Taiwan, for example, geomorphic provinces have been delin-eated on the basis of self-affinity dimensions of landscape sur-faces and on the morphotectonic features of orogenic belts(Sung & Cheng, 2004). Yang et al. (2002) defined geomorphicprovinces along the Keriya River in China based on the rela-tionship between environmental change and landscape evolu-tion. Similar concepts have been developed for systems in theUnited States (Montgomery & Buffington, 1998).

    Delineating geomorphic provinces for South Africa,Lesotho and Swaziland

    Advances in the fields of geology, remote sensing and geo-morphology, the disciplines of stratigraphy, seismology, radio-metric and isotopic dating, and current information generatedfrom on- and off-shore exploration, require the revision ofSouth Africas, Lesothos and Swazilands geomorphic prov-inces1 for the purposes of systematic conservation planning.The inductive approach adopted here has been to revise andrefine the boundaries of earlier geomorphic provinces utilisingthe latest scientific literature and a statistical examination of99 selected main stem river longitudinal and valley cross-sectional profiles generated from a Digital Terrain Model(DTM). This approach applies state-of-the-art views andmethodology appropriate to the objectives of this new subdivi-sion.

    River longitudinal profiles have been utilised because theyreflect the influence of lithological change, tectonics, river cap-ture, climate change and historical changes in base-level; theyalso provide a common focal point for physical scientists andecologists [e.g., through the river continuum concept (Vannoteet al., 1980; Brown & Magoba, 2009)] in selecting physical signa-tures as surrogates for freshwater ecosystem biodiversity at ascale appropriate to national and sub-national biodiversityplanning initiatives. In southern Africa, these influences haveresulted in many rivers being characterised by irregular longi-tudinal profiles (Partridge & Maud, 2000). Such irregularitiesmark natural boundaries along the profile continuum (e.g.,knick-points, lithological changes) and these are also oftenthe boundaries between geomorphic provinces. Accordingly,longitudinal profiles can be divided into homogenous zones orreaches (termed macro-reaches in this article) separated bylongitudinal discontinuities (Dollar et al., 2006). The delinea-tion of macro-reaches for this purpose is not without prece-dent. Macro-reaches have been used, for example, to dividerivers into zones of similar form and response (cf. Rowntree &Wadeson, 1999; Rowntree, 2000; Heritage et al., 2000; Baillie &Norbu, 2004). One of the assumptions underlying these divi-sion...