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KEURBOOMS RIVER ESTUARY: Catchment Characteristics

Main Rivers and tributaries

The Bitou river is the main tributary of the Keurbooms river   (Ref 1)

Dams
Roodefontein Dam is being raised by the Plettenberg Bay Municipality.

River run-off
In 1969, the Keurbooms River maintained a mean annual runoff of approximately 127 x 106 m3.  In 1981 the mean annual discharge into the Keurbooms River exceeded 72,9 x 106 m3 (Ref. 2).  In 1975, the flow of the Keurbooms River is below 0,30 m/s, even at springtide, due to the high friction coefficient of the river (Ref. 5).  The mean annual Runoff (MAR) of the Keurbooms River , as reported in 1999, was 207 x 106 m3.     (Ref 1)
The mean annual run-off of the Keurbooms catchment is 215 million m3 .   (Ref 1)
According to river flow data obtained from the Division of Hydrology, (Department of Water Affairs, in litt.), the mean annual run-off of the Keurbooms River system over the ten-year period, 1960/61 to 1969/70, was calculated to be 64 x 106 m3 , measured at the gauging station at Newlands 15 km upstream from the mouth (Department of Water Affairs Station No. K6M02, River flow data (1978)).
A value of 71 x 106 m3  was calculated over the period October 1970 to June 1981 at the same station.  Although this station is relatively close to the mouth and below the confluence of the major tributaries, the values are much lower than those estimated by Midgley and Pitman (1969).

The values were calculated from different data sources (rainfall versus gauging plate measurements) but this descrepancy is probably due to the discharge regularly exceeding the table limit and thus the capacity of the measuring station.  (Ref 1)

Geomorphology
Geomorphologically and geologically, both rivers consist of an upper and lower section.  The upper section is cut into the elevated coastal terraces of the hinterland, in contrast to the lower section, where the estuary spreads onto the coastal plains.

After the two estuaries have combined into one, they form the actual back-barrier estuary against the recent barrier dune ridge.  This ridge forms the core of the two long and massive sand spits which meet at the permanently open estuary mouth. (Ref 1)

Geology

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