GROOTBRAK RIVER: Topography, geology and soils

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Map of the GROOTBRAK River

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TOPOGRAPHY
The Great Brak river rises on the slopes of the Engelsberg in the Outeniqua Mountain range 25km in a straight line from the river mouth.  The catchment is relatively long and narrow being about 25km long and reaching a maximum of about 8 km in width.  Much of the river system drains an elevated coastal platform 150 - 300m high.  (Ref 1)
Between the village of Great Brak and the Garden Route Freeway bridges the river meanders through a wide floodplain.  Immediately seaward of the freeway bridges the river enters the lagoon basin about 1km long and 0,5km wide.  The basin is bounded by the hilly coastal plain in the north and by the approximately 30m high bush-covered dune ridge to the south.  The dunes east of the mouth form a bluff about 50m high consisting of 20 m basal dune rock, probably of Tertiary age, overlain by a partly vegetated field of transverse barchan-type dunes.  The Hersham residential area has been developed in this area.  (Ref 1)
    GEOLOGY                                    
The headwaters of the Great Brak rise on the quartzitic sandstones of the Peninsula Formation of the Table Mountain Group.  These sandstones, forming the spine of the Outeniqua Mountain range, display the characteristic east-west strike of the folded rocks of this area.  The strata of the Peninsula Formation dip southwards.  The Great Brak runs southwards through the quartz schists of the Sandkraal Formation is extensively thrust faulted; this is a legacy of the orogenic processes that gave rise to the mountains of the Cape Fold Belt.  To the south of the Sandkraal Formation the river runs on Tertiary/Quarternary valley alluvial deposits lying between bluffs consisting of gneissic granite, granodiorite and albitite intrusions of mid-Namibian age.  Closer to the sea the valley alluvial deposits lie between the reddish mudstones and sandstones ("Poortjie sandstone") of the Teekloof Formation of the Adelaide Subgroup of the Beaufort Group (Karoo Sequence).  The heights to the east of the river consist mainly of Cretaceous conglomerates of the Enon Formation.  Finally the river enters the sea via an estuary mouth consisting mainly of quartzitic aeolian and marine sands.  The mouth is bounded to the east by  low aeolianite ( dune rock) cliffs. (Ref 1)
    SOILS                                    
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