BERG RIVER: Topography, geology and soils


Map of the Berg River

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The Berg River Catchment covers an area of almost 9 000 km2 and is the largest catchment in the Western Cape Province . Based on geographic and topographic characteristics, the catchment can be divided into three distinct areas, namely the broad, flat extensive western portion west of Moorreesburg and Koringberg, the river valley portion east of Koringberg to just south of Paarl, and the upper mountainous source area south of Paarl. Major towns in the western portion include Saldanha, Vredenburg and Hopefield while key towns in the central river valley area include Piketberg, Porterville, Paarl and Wellington. Franschhoek is found at the base of the Franschhoek Mountains some 6 km north east of the proposed Berg River Dam site . The total population of the catchment is in the order of 200 000, most of whom live in the urban areas. (Ref4)

Much of the catchment area is flat, with an average topographical gradient between Paarl and the mouth of the Berg River at Laaiplek of 0.001. Topographically, a north-trending ridge of mountains (Piketberg, Swartberg) divides the catchment in two, with the Berg River flowing through a poort between Koringberg and De Hoek. Mountains that reach in excess of 1 000 m elevation flank the north trending valley in the eastern part of the catchment, including the Groot Winterhoek Mountains, Kasteelberg, Perdeberg, Paarl Mountain and the Wemmershoek Mountains. (Ref4)

The Berg River Upstream of Hermon :   This sub-area  extends from the source of the Berg River in the Groot Drakenstein Mountains, to the flow gauging station at the bridge near the town of Hermon. It covers an approximate area of 1 310 km2. The topography is characterised by high mountain ranges in the south and east which drain towards the Berg River. (Ref 3)
The Klein Berg River:  The sub-area  has an approximate area of 390 km2. The Tulbagh Valley is bounded in the east by the Witzenberg Mountains and in the north by the Groot Winterhoek Mountains. (Ref 3)
Berg River Downstream of Hermon:  The sub-area  covers an approximate area of 7 450 km2. (Ref 3)
The Berg River rises in the Franschhoek and Drakenstein mountains at an altitude of 1500 m. It flows northwards past Paarl, Wellington, Hermon and Gouda, where it is joined by the Klein Berg and Vier-en-Twintig rivers. The river then flows westwards past Porterville, Piketberg and Velddrif where it finally discharges into St. Helena Bay on the west coast. (Ref 2)
The profile of the Berg River (from the origin near Franschhoek to the mouth at Velddrif)  is illustrated below:
Upper Berg river:   Table Mountain Group (quartzitic sandstone), Sandy sediments   (Ref 2)
Upper Middle Berg River:  Table Mountain Group (quartzitic sandstone), Malmesbury Group (shale), Cape Granite Suite, Sandy sediments   (Ref 2)
Lower Middle Berg River:  Table Mountain Group (quartzitic sandstone), Malmesbury Group (shale), Klipheuwel Group, Sandy sediments   (Ref 2)
Lower Berg River:   Table Mountain Group (quartzitic sandstone), Malmesbury Group (shale), Cape Granite Suite, Sandy sediments  (Ref 2)

The Berg River Catchment comprises sequences of rocks of the Malmesbury Group, the Cape Granite Suite, the Klipheuwel Group, the Table Mountain Group and younger Cenozoic sediments in the western part of the catchment. The Malmesbury Group and Klipheuwel Group essentially comprise soft, erodible rocks that form flat plains in low lying areas. In general, these areas have moderate to high agricultural potential. The Malmesbury Group is steeply folded along a north west striking axis (Visser 1989). These metasediments form part of the Saldania Subprovince and have been subdivided into three tectono-stratigraphic domains, i.e. the Tygerberg, Swartland and Boland domains. These domains are separated by two major north-northwesterly striking fault systems, namely the Franschhoek-Saldanha (Colenso Fault) and Wellington-Piketberg Faults (Visser 1989). (Ref 4)

Outcrops of Cape Granite Suite rocks occur in the west, south and south east of the catchment. This series of granitic plutons, of late Precambrian to early Cambrian age, intruded into Malmesbury Group. Older intrusions occurred between 610 and 560 Ma, while the younger phase occurred between 540 and 500 Ma (Timmerman 1988). In places they form prominent features like the Paarl Mountain.  (Ref 4)

The Table Mountain Group comprises hard resistant quartzitic sandstones that form the mountain ranges that flank the north-trending river valley in the east. The rocks have been folded and faulted, giving them their secondary water-bearing features. (Ref 4)

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The siliceous Table Mountain Group (TMG) produces soils that are acidic and infertile. (Ref 4)

Soils derived from the Cape Granite are also more fertile and finer textured than those derived from the Table Mountain Group. (Ref 4)



Ref 3:  Department of Water Affairs and Forestry, South Africa. 2004. Berg Water Management Area: Internal Strategic Perspective. Prepared by Ninham Shand (Pty) Ltd in association with Jakoet and Associates, Umvoto Africa and Tlou and Matji, on behalf of the Directorate: National Water Resource Planning. DWAF Report No P WMA19/000/00/0304.

Ref 4: Berg River Baseline Monitoring Programme -  Introduction to the Berg River Catchment; Groundwater and Hydrology DWAF Report No. P WMA 19/G10/00/1807 Edited by: GEORDIE RACTLIFFE
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