The study area is situated in the southern cape region within the greater Breede-Gouritz Water Management Area (WMA) of South Africa between latitudes 33° and 35° south and longitudes 20° and 24° east. This WMA falls predominantly within the Western Cape Province (53 139 km2), with small portions in the Eastern Cape and the Northern Cape Provinces. The study district level (Eden District) and catchment level (Wilderness river catchment). The study area is in the Eden District.
Eden extends from the Breede River in the west to the Bloukrans River in the east and is flanked by the Indian Ocean with 340 km of coastline and the Swartberg Mountain Range inland. It is characterised by a rugged terrain with diverse topography.
The Wilderness catchment forms part of the Garden Route coastal catchments and comprises a quaternary catchment (K30B) in the national catchment naming system. The catchment area is extends from the coastline in the south to the crest of the Outeniqua mountains in the north with maximum elevation of 1 200 mamsl. This catchment can be divided into two main subcatchments, the Touws River including the estuary (10 219 ha), and the lakes with their rivers (7 306 ha) as seen in the figure below.
The climate varies significantly on either side of the Outeniqua Mountains which forms a natural barrier separating the coastal region from the semi-arid interior. The difference in climate is evident in the annual rainfall which averages between 700 mm and 1200 mm along the coast, and less than 400 mm in the interior (e.g. Little Karoo). The rainfall is fairly evenly distributed throughout the year with peaks in autumn and spring. The high rainfall on the coastal ridge also means that the rivers draining the lower Touws River and the lakes receive more rainfall than expected. For example, the mean for the Touws River has been estimated as 915 mm/yr while for the Langvleispruit River it was 900 mm/yr. Temperatures are generally moderate. The absolute minimum temperatures can reach 0°C and the absolute maximum temperatures can reach 40°C. The humidity is high because of the proximity to the sea, but dry hot conditions occur during Berg winds which occur mainly in the winter months.
The shallow soils and limited groundwater storage of the TMG quartzitic sandstones make the river flows highly responsive to rainfall. Both the pH (4-5) and electrical conductivity (< 20 mS/m) are typically low. The Outeniquas Mountains form the headwaters of the Touws River. It is supplied by some important tributaries and flows directly into the estuary on the western side of the catchment. The Duiwe River (93.7 km) drains into Eilandvlei and has its headwaters on the coastal ridge and two perennial tributaries, Woodville (21.0 km) and Klein Keurbooms (27.86 km). A large number of farm dams have been built and the abstraction of irrigation water from them accounts for most of the reduction in river flows in the Duiwe and Langvleispruit. These agricultural abstractions resulted in the Duiwe changing from perennial to non-perennial. Moreover, the flow at the weir downstream on the Duiwe is generally low and irregular with frequent no-flow periods. Short-lived high flows after heavy rains alternate with periods of sustained flows (e.g. 1996-1997) and prolonged periods with virtually no flow (e.g. 2008-2010). The Langvleispruit River is of a similar size (21.2 km) but has lower runoff rates and is ephemeral due to intensive farming in the catchment.
The study area supports a diverse plant life which has adapted to the physical conditions. The vegetation is situated in an area where four biomes (Fynbos, Succulent Karoo, Thicket, and Forest) converge. It forms a central part of the Cape Floral Kingdom. Fynbos vegetation types largely dominate (Mucina and Rutherford, 2006). Eden is well known for its diverse natural areas (e.g. nature reserves, national parks and unspoilt coastline). Large parts of the area’s vegetation is still unconverted with 63.46% consisting of indigenous shrubland and fynbos vegetation and a further 8.1% consisting of thicket and bushland (although natural vegetation is heavily grazed in places). Agricultural activities associated with crop cultivation and plantation forestry have transformed a further 18.58% of the landscape.
The town of Wilderness was founded in 1877. It is a nationally important tourist attraction. Wilderness became a very popular area for holidays and the numbers of tourists rose steadily but it was only after the 2nd World War that tourism took off as the South African economy boomed from the late 1950s to the 1970s. This is when most of the older housing developments in Wilderness, Wilderness East, Hoekwil and other locations around the lakes were build.