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Main
Rivers and tributaries |
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Mkomazi River
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Dams |
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River
run-off |
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1978 (Ref.1): Over the period 1965 to
1967 the mean annual discharge was estimated to be in the vicinity of 30
m3/sec. Seasonal flows range from an average of 42 m3/sec.to
48m3/sec. in summer, and from 10 m3/sec to 12,5 m3/sec.
in winter.
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Geomorphology
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Geology
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"The
river traverses a whole succession of geological formations in its
catchment ranging from old granites to Stormberg series . From recent
investigations at the site of the new bridge, boring has revealed that
in excess of 80m of sediments overlie bedrock in certain places. This situation is very
different to that described by Orme (Ref.3) who described
Karroo
dolerite as bedrock 18m below mean average sea level on the northern
bank of the estuary. Dolerite also outcrops at the coast, on the
southern side of the estuary mouth.
It appears to form a sill (or resistant ledge) across the estuary, which
retards down cutting." (Ref 1)
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Nature of bottom
materials.
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1978 (Ref.1): "The estuary has been described as a “sand choked” system. Black silt
is found 7 m to 15 m below such deposits. Day mentions “thigh deep”
mud banks on the southern bank of the estuary in the 1950’s. Near the
mouth, the overlying deposits are medium to coarse-grained
“washover” marine sands. They were found to be coarser if deposited
on a flood tide than if deposited on an ebb tide. An aerial photograph
(date 15 May 1971) clearly shows that a centrally positioned island,
called Chocolate Island periodically appears +/- 1 km from the mouth.
This develops as a result of deposition during years which are not
associated with flooding. Severe floods (such as in
1959 or 1976) wash the island away during the course of channel
migrations."
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Sandbar
characteristics.
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1978
(Ref.1): "The Mkomazi
sandbar is normally a massive, south-directed feature. However, the
mouth position can migrate from its normal southerly position during or
after floods. It may close completely in the dry season but this
is a rare occurrence. Van Heerden found the mean size of the spit
material (as an indication of maturity) to decrease northwards. He
suggests spit growth (or progradation) in a southerly direction was by
over wash and beach drift. On the other hand, spit growth in a northerly
direction occurred under the influence of the long shore current and
southerly swells, when flood materials forming under and offshore bar
were available. Breaching is normally not necessary, although ski-boat
owners have been known to encourage the mouth position to switch from a
northerly position (such as that on 25 July 1976) to a more southerly
position by breaching. They do this in order to create a more
conventional point of exit for their boats".
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