LOURENS RIVER: Topography, geology and soils

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Map of the LOURENS River

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TOPOGRAPHY
The Lourens River rises in the deep kloofs of folded mountains, passes through a shallow valley surrounded by undulating hills and finally cuts across the flat coastal plain before emptying into the sea.  (Ref 1)
    GEOLOGY                                    

The landscape of the Lourens Valley is derived geologically from the Cape Fold belt consisting of a band of parallel ranges of quartzitic sandstone ridges with intervening undulating valleys of shale and outcrops of Cape granite.  The earliest deposits are over 400 million years old, but the mountain ranges are more recent, having been formed some 200 million years ago.  There are also small pockets of ferricrete (koffieklip/ysterklip) found in the shale-derived valley. These date from about 20 million years ago when sea levels were much higher. Despite the apparent verdure, the soils are mostly acidic and infertile. This geological landscape has remained unchanged for over 65 million years (Aikman Associates, 2005).

The Hottentots Holland Mountains consist mainly of Table Mountain sandstone.  There are, however areas of shallow soils, overlying shale and greywacke of the Malmesbury group.  The hills surrounding the river comprise shallow soils, overlying granite of the Cape Granite System.  (Ref 1)

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    SOILS                                    
The river valley is largely overlain by an alluvial sediment layer, comprising boulders and clay, of more than 2m.  Near the mouth the transported soils comprise mostly sand (MJ Mountain & Associates 1: 50 000 Engineering geological map of the Somerset West and Hangklip areas).   (Ref 1)
  References                                      

Ref 1: Estuaries of the Cape Report No. 17 Lourens (CSW 7) CSIR RESEARCH REPORT 416.

Ref 2:  DWAF, 2003.  State-of-Rivers Report, River Health Programme (2003).  Diep, Hout Bay , Lourens and Palmiet River Systems.

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