PALMIET RIVER

PALMIET RIVER: Topography, geology and soils

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Map of the PALMIET River

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TOPOGRAPHY

The Palmiet River rises in the vicinity of Landdroskop (1 133m) in the Hottentots Holland Mountain Range. Initially it flows in an easterly direction, dropping rapidly in altitude over the first few kilometers (about 400m in 4 km). About 4 km from its source, the river leaves the steep slopes of the Hottentots Holland Range and swings south towards Grabouw, approximately 12km away. (Ref 2)

From here to the Eikenhof Dam, the river flows down the less steep foothills between the Hottentots Holland Range and the Groenlandberge. The gradient in this region is still steep but not nearly as dramatic as in the upper regions (about 300m in 9 km). (Ref 2)

Just before the Eikenhof Dam, the river enters the Elgin Valley. From here to the sea, the slope of the land traversed by the river is extremely mild, dropping approximately 300 m over a distance of about 60 km. For the next 35 km the river flows close to the western boundary of the Elgin Valley, flanked by the foothills of the Kogelberg mountains on its west bank and the cultivated lands of the valley on its east bank. It flows in a southerly direction until its junction with the Klein Palmiet where it swings north-east for about 6km before swinging south again. About 15 km from the mouth, the river leaves the Elgin Valley and enters the deep valley between the Dwarsrivierberg and Perdeberg ranges. (Ref 2)

It flows predominantly in a south-westerly direction until the junction with the Louws and Dwars rivers where it swings sout-east and heads for the sea. Near the coastal road which traverses the river, the river begins to broaden out into an estuary about 1.67 km long. The coastal plain at the mouth is extremely narrow so that the river changes from a mountain stream to an estuary with no intervening stretches typical of a lower river. (Ref 2)

GEOLOGY

The vegetation is dominated by mountain fynbos with pockets of afromontane forest in the river ravines and renosterveld along the coastal strip. The geology is mostly Table Mountain Sandstone with some shale which results in a high surface runoff of low salinity, acidic water. (Ref 1)

GEOMORPHOLOGICAL ZONES:

Lower Foothill Zone: This zone has a lower gradient with an alluvial bed of sand and gravel which may be bedrock dominated. The zone is characterised by more pools than rapids or riffles, with sandbars common in the pools. A floodplain is often present.

Upper Foothill Zone: River reaches in this zone are moderately steep with cobble or mixed bedrock-cobble bed. This river zone is characterised by similar pool and rapid/riffle lengths.

Mountain Stream Zone: This zone is characerised by a steep gradient, dominated by bedrock and boulders, with cobble and coarse gravels in pools. Water flows in cascades, waterfalls and pools. (Ref 1)

The geology of the Palmiet River catchment is dominated by Table Moutain Group sandstones, quartzites and shales and Bokkeveld shales and sandstones. Witteberg Group quartzites and shales occur to a lesser extent. (Ref 2)

The mountain and foothills of the catchment consist predominantly of the sandstone and quartzites of the Nardouw Formation. Sandstones and quartzites of the Peninsula Formation, which are generally more resistant to weathering, occur in the northern and south-western mountainous regions of the catchment and along the coast. (Ref 2)

SOILS

References

Ref 1: State of rivers report- Diep, Hout Bay, Lourens and Palmiet River Systems- 2003

Ref 2: Estuaries of the Cape Report no 37: Palmiet (CSW 12) CSIR RESEARCH REPORT 436

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