Chapter 2: Overview of the Olifants/Doorn WMA 15 CHAPTER 2 OVERVIEW OF THE OLIFANTS/DOORN WMA The Olifants/Doorn WMA derives its name from the main river draining it, namely the Olifants River. The word "Doorn", an archaic form of Doring, was added to the WMA name to distinguish it from the many other "Olifants" rivers in the country as the Olifants River's main tributary, in this catchment, is the Doring River. The WMA is bounded in the west by the Atlantic Ocean, and its eastern boundary lies along the Great Escarpment divide between the Great Karoo and the western branch of the Cape Fold Belt. The major water user of the area is irrigated agriculture, which sustains the economy of the area and provides most of the employment opportunities. Parts of the WMA have high conservation value, including some of the river reaches and the Olifants River estuary. This chapter provides an overview of the WMA. Chapter 3 provides more detailed information on each of the six sub-areas into which the WMA has been divided and Chapter 4 provides an overview of its water resources. 2.1 LOCALITY AND PHYSICAL FEATURES 2.1.1 Locality and Development The Olifants/Doorn WMA is located on the west coast of South Africa, extending from about 100 km to 450 km north of Cape Town. The south-western portion mainly falls within the Western Cape Province, and the north-eastern portion falls within the Northern Cape Province. Refer to Figure 2.1 for the location and general layout of the WMA. The major river in the WMA is the Olifants River, of which the Doring River (draining the Koue Bokkeveld and Doring area) and the Sout River (draining the Knersvlakte) are the main tributaries. The WMA incorporates the E primary drainage region and components of the F and G drainage regions along the coastal plain, respectively north and south of the Olifants River estuary, covering a total area of 56 446 km2. The Olifants and Doring Rivers flow strongly during the winter months whilst flows only occur very occasionally in the Sout River. There are also a number of smaller coastal rivers and water courses which flow infrequently. 2.1.2 ISP Sub-areas The WMA comprises 88 quaternary catchments and has been divided into six sub-areas2 or "management units", corresponding to the current divisions used in surface water resource management by the Regional Office of the DWAF. Refer to Figure 2.2 for the ISP sub-areas. 2 The Olifants Doorn WMA was divided into only five sub-areas in the National Water Resource Strategy (NWRS). The Olifants River sub- area as defined in NWRS has been spilt into two for the purpose of this ISP (Upper Olifants and Lower Olifants). It was recognised that the two sections of the river have distinctly different water resource management characteristics. February 2005 Figure 2.1: Map of the Olifants/Doorn Water Management Area Figure 2.2: Map of the Olifants/Doorn ISP Sub-areas Chapter 2: Overview of the Olifants/Doorn WMA 18 These sub-areas are as follows: • The Upper Olifants sub-area consisting of seven quaternary catchments (E10A-G), extending from the source of the Olifants River to the Clanwilliam Dam; • The Koue Bokkeveld sub-area consisting of 11 quaternary catchments (E21A-L) draining in a northerly direction from the catchment divide between this WMA and the Breede WMA; • The Doring sub-area consisting of 32 quaternary catchments (E22A-G, E23A-K, E24A- M, E40A-D) draining the south-eastern and central region of the WMA to the confluence with the Olifants River; • The Knersvlakte sub-area consisting of 24 quaternary catchments (E31A-H, E32A-E, E33A-F, F60A-E) and draining the northern region of the WMA; • The Lower Olifants sub-area consisting of six quaternary catchments (E10H, J, K, E33F- H,) downstream of Clanwilliam Dam; • The Sandveld sub-area consisting of 8 quaternary catchments (G30A-H) within the coastal strip to the south of the Olifants River mouth. 2.1.3 Climate and rainfall Climatic conditions vary considerably as a result of the variation in topography. Minimum temperatures in July range from –3ºC to 3ºC and maximum temperatures in January range from 39ºC to 44ºC. The area lies within the winter rainfall region, with the majority of rain occurring between May and September each year. The mean annual precipitation is up to 1 500 mm in the Cederberg mountains in the south-west, but decreases sharply to about 200 mm to the north, east and west thereof, and to less than 100 mm in the far north of the WMA. Average gross mean annual evaporation (as measured by Symons pan), ranges from 1 500 mm in the south- west to more than 2 200 mm in the dry northern parts. Scenarios of climate-change over the next 50-100 years show this area may potentially receive up to 15% less rain in future (refer to Figure 2.3). 2.1.4 Topography The topography of the WMA is of three distinct types, namely rolling hills and sand dunes in the west along the coastal strip, rugged mountains with peaks rising to about 2 000 m above sea level in the southern area, and plains and rocky hills in the north-eastern area that are typical of the Western Karoo (Figure 2.4). The Olifants River rises in the mountains in the south-east of the WMA and flows north-west. Its deep narrow valley widens and flattens downstream of Clanwilliam until the river flows through a wide floodplain downstream of Klawer. The Doring River is a fan shaped catchment. The main river rises in the south and flows in a northerly direction. It is first joined by the Groot River and then by the Tra-Tra flowing from the west and the Tankwa River from the east, before flowing in a westerly direction to its confluence with the Olifants River just upstream of Klawer. February 2005 Figure 2.3: Rainfall and evaporation Chapter 2: Overview of the Olifants/Doorn WMA 20 The north of the WMA is flatter and much of the basin lies between 500 and 900 m above sea level. In the east there are significant mountain ranges, the Hantam near Calvinia and the Roggeveld to the south, which rise to about 1 500 m above sea level. West of Nieuwoudtville lies the Bokkeveld Mountains escarpment where the plateau elevation of about 700 m drops to about 300 m. The rolling hills and plains of the 30 to 40 km wide strip along the coast from the southern boundary of the WMA to the estuary of the Olifants River are known as the Sandveld. The deep sandy deposits overlaying the bedrock in this area are "primary" aquifers which provide a significant groundwater resource. 2.1.5 Geology The geology of the area is dominated by sedimentary rocks of the Table Mountain Group (TMG) of the Cape Supergroup, which form the highest (almost north/south trending) mountain ranges. The rocks of the Karoo Supergroup outcrop occur largely in the eastern and northern areas of the catchment of the Doring River and comprise the valley floors of the Olifants River where it overlies the TMG. Sedimentary strata of the Vanrhynsdorp Group occur in the north, with exposures of pre-Cape metamorphic rock in the north-western and north-eastern corners of the area. The coastal plain is variably underlain by the metamorphosed shales of the Malmesbury Formation and the sandstone of the TMG. These are overlain by the more recent semi to unconsolidated sediments of alluvial, wind-blown (Sandveld Group), and marine origin as well as calcrete and ferricrete deposits. Table 2.1: Geology and Hydrogeology of the Olifants/Doorn WMA Hydrogeological Province ISP sub-areas Geology/Hydrogeology Aquifers (Sub-province) Adamastor Sandveld - Tertiary-Quaternary alluvials Upper Olifants - Sandveld Group W Koue Bokkeveld (E21G, H, - (Bokkeveld Group) Tertiary-Quaternary Cederberg J, K) - Table Mountain Group (TMG) alluvials W Lower Doring (E24A, J, L, M, - Klipheuwel Group Sandveld Group lower part of E24K) - Cape Granite Suite Skurweberg Aquifer Lower Oorlogskloof (E40D) - Malmesbury Group Peninsula Aquifer - Sandveld Group Sandveld Group - (upper TMG) Lower Olifants/Sout Knersvlakte - Nama Group Goerap Nama quartzites and - Gariep Group limestones - Namaqua Metamorphic Complex (NMC) Western Karoo - Tertiary-Quaternary alluvials Upper Doring - Lower Beaufort Group Tertiary-Quaternary E Koue Bokkeveld (E21A-F, L) - Ecca Group alluvials Tankwa Karoo Tankwa - Dwyka Formation Witpoort Aquifer E Lower Doring (E24B-H, upper part - Witteberg Group (in S) Bokkeveld sandstones of E24K) - Bokkeveld Group - (upper TMG) - Tertiary-Quaternary alluvials Alluvials in Calvinia - Karoo dolerites Upper Oorlogskloof (E40A-C) - Ecca Group Karoo dyke and sill Hantam Hantams - Dwyka Formation structures, in conjunction Kromme - (upper TMG) with sandstone members in - (Nama Group) otherwise generally shaly - (NMC) units February 2005 Figure 2.4: Topography Chapter 2: Overview of the Olifants/Doorn WMA 22 2.1.6 Vegetation Due to the diverse soil types and variance in rainfall distribution, vegetation is varied and includes at least six veld types and several thousand plant species. Karoo and Karroid Types, False Karoo Types, Temperate and Transitional Forest Types, Scrub Types, and Sclerophyllous Bush Types dominate the Olifants/Doorn WMA and these are described in more detail below. Karoo and Karroid types dominate the WMA, occupying some 75% of its area. The flora is characteristically low, typically less than 1 m in height, and includes scrub, bushes, dwarf trees and a few grasses. This vegetation type occurs where rainfall typically ranges between 150 mm and 500 mm, but does reach a maximum of up to 900 mm in some of the river valleys.