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Published by WAMTechnology, 2017-06-02 05:16:51

GOURITS ESTUARY

GOURITS ESTUARY





The Gourits River Estuary is situated approximately 27 km south of the
N2 highway between Albertinia and Mossel Bay.
35°21’S; 21°53’E
The Estuarine characteristics of the Gourits River stretch about 10km
upstream from the mouth (Ref. 1). The Gourits Estuary has a total
surface area of 188ha

Ref.3. Duvenhage, I. (1983). Getyrivieroppervlaktes van sommige getyriviere
aan die Kaapse kus. Stellenbosch. NRIO unpublished report



The Gourits River is formed by the confluence of the Gamka
and Olifants Rivers, south of Calitzdorp.
The Olifants River is fed by 12 tributaries, originating in the
Groot Swartberge and the Kammanassieberge.
The Gamka is fed by numerous tributaries, originating in the
Nuweberge.
The Buffels River, rising from the Nuweveld Mountains, joins
the Groot River, along with the Touws River from the west. The
Groot River then joins the Gourits.

The total river length of the Gourits River is approximately 1 045km.
It enters the Indian Ocean about 33km south-west of Mossel Bay (35º
21‘S; 21º 53’E).
The Gourits River Catchment stretches from the Karoo in the north, to
the coast in the south. It is the third largest catchment in South Africa
and comprises approximately 45 000 km2.

Stompdrif Dam

There are 10 large dams on the
Gourits River of which the Floriskraal
Dam (62 900 000m3) on the Buffels
River, the Gamkaspoort Dam (54
300 000m3) on the Gamka River, the
Kammanassie Dam (32 900 000m3)
on the Kammanassie River and the
Stompdrif Dam (61 200 000m3) on
the Olifants River are the most
important.

Gamkapoort Dam

The grain size of the sand spread along the whole sandspit and the adjacent
beach in 1987 was medium and ranged from 210 to 468 microns, with a mean
grain size of 342 microns.

Ref.1. Heydorn, H.J. (1989). Estuaries of the Cape. Part II: Synopses of available information on individual
systems. Report No. 38 Gourits (CSW 25). CSIR Report 437, 66pp.
Ref.2. Pitman, M.V. et al. (1981). Surface water resources of South Africa. Vol. IV. Drainage regions E G H J K L,
Western Cape Water Research Commission. Hydrological Research Unit Report 13/81. Parts 1 and 2





The small resort of Gouritsmond is situated on the west bank of the
estuary near the mouth.

The closest towns are Albertinia, Vleesbaai and Mossel Bay.
The main farming activities are sheep and cattle farming and fodder crops.
The cattle are mostly for meat production, but a few dairy herds are also
kept. The crops include lucern, siradellon and oats. Wheat and maize were
also cultivated in the area in 1989.

The estuary itself is used for water sports, such as power boating, water
skiing, canoeing, yachting, swimming and angling. Prawns, used for bait,
are collected from the mudflats in the estuary.

Ref.1. Heydorn, H.J. (1989). Estuaries of the Cape. Part II: Synopses of available information on individual
systems. Report No. 38 Gourits (CSW 25). CSIR Report 437, 66pp.
Ref.4. Summers, R.W., Pringle, J.S. and Cooper, J. (1976). The status of coastal waders in the South Western
Cape, South Africa. Cape Town. Percy Fitzpatrick Institute of African Ornithology. 162pp





Two veld types of terrestrial vegetation were represented in the lower
reaches of the Gourits River, namely the Coastal Renosterveld and the
Coastal Macchia

Eleven vegetation types have been identified:
Arid scrub thicket : Dominant tree species are the

Sideroxylon inerme and the Euclea racemosa. Sub-tropical
thicket species include Rhus longispina and Scolopia zeyheri.
Other locally conspicuous species are the white aloe and
Euphorbia species.

Renosterveld : The species composition is secondary in
response to the impacts of fire and stock pressure and
although considered to be relatively diverse, it is dominated by
Elytropappus rhinocerotis. Other dominant genera include
Eriocephalus, Anthospermum, Passerina, Relhania,
Aspalathus, Helichrysum, Pteronia, Selago, Felicia and
Hermania.

Strandveld: The area consists of a mosaic of bushclumps,
restios and shrubs, with a conspicuous graminoid and
herbaceous ground layer (Ref. 1). The bushclumps are
dominated by Sideroxylon inerme, Schotia afra and
Pterocelastrus tricuspidatus (Ref. 1). The dominant restio
species are Thamnochortus bachmannii, Chrysanthemoides
monilifera and Phylica axillaries var. maritime (Ref. 1). The
herbaceous ground layer comprises mainly Themeda triandra
and Agathosma muirrii .

Strandveld-thicket mosaic: The dominant woody species
include Euclea racemosa, Sideroxylon inerme and Rhus
longispina. The dominant shrub in the area is Zygophyllum
morgsana. Two aloe species occur, namely Aloe ferox and A.
arborescens.

Dune scrub: The dense scrub is dominated by Euclea
racemosa, Tetragonia decumbens, Trachyandra divaricata,
Salvia africana-lutea and Restio eleocharis

Dune shrubland : Dominant shrub species include Myrica
cordifolia, Chrysanthemoides monilifera and Stoebe plumosa.
Common grasses are Ammophila arenaria, Ehrharta villosa
and Senecio elegans

Acacia cyclops thicket: Scattered clumps of the exotic
species, Acacia cyclops occur. It can spread rapidly and
should be eradicated .

Saltmarsh : The saltmarsh vegetation is not
particularly well developed. Sarcocornia pillansiae is
dominant on both banks at the mouth. Other species
include Chenolea diffusa, Sporobolus virginicus,
Juncus acutus, J. kraussii and Phragmites australis.
Cotula coronipifolia and Triglochin species occur at the
lower tidal levels, forming saltmarsh lawns.

Dune thicket : A dune thicket of up to 3m occurred
on the western bank of the estuary. The most
conspicuous species are Sideroxylon inerme, Euclea
racemosa, Pterocelastrus tricuspidatus and Clausena
anisata

Limestone fynbos: The most common protea
species are Protea repens, P. susannae, and P.
lanceolata, as well as Leucospermum praecox and
Leucadendron galpinii. Heavy infestations of the
exotic Acacia cyclops were evident in 1989 .

Secondary grassland: This secondary grassland
use to be fynbos, but was converted by agriculture

Ref.1. Heydorn, H.J. (1989). Estuaries of the Cape. Part II: Synopses of available information on
individual systems. Report No. 38 Gourits (CSW 25). CSIR Report 437, 66pp
Ref.12. Underhill, L.G. and Cooper, J. (1983). Counts of waterbirds at coastal wetlands in South Africa:
Estuaries 1979-1981. Unpublished Computer Printout. Western Cape Wader Study Group and Percy
FitzPatrick Institute of African Ornithology





During a survey in 1987 (Ref.1), the top and bottom water samples were
taken at 4 stations. Readings were taken for Temperature, Dissolved
oxygen, salinity, and water transparency. It was concluded that the water
was well oxygenated with dissolved oxygen values just below saturation.
Salinity and temperature values indicted fairly good mixing at most
stations. Water transparency varied between 1.1 and 2 m (Secchi disk
measurements), with the water colour being varying intensities of green

Interesting: References to pollution incidents. An article in “Die Burger” of
16 July 1982, which reported on the death of fish in the Gourits River, most
probably caused by vinegar like substance resulting in oxygen depletion.
Thousands of dead moggels (Labeo umbratus) were found as far
upstream as Herbertsdale (100km inland). A press release from the
CDNEC on 19 August 1987, which reported the death of 15 blue cranes
through poisoning on the banks of the Gourits River near Herbertsdale



The tidal lag in the estuary was in
1987 approximately 2 hours at low
tide , at the head of the estuary.

Saline water seemed to penetrate up
to 2 km upstream of the road bridge
at “Die Eiland” during high tide. This
point is the absolute upper limit of
estuarine conditions as confirmed by
the vegetation.

The mouth of the Estuary is normally
about 18m wide but during the rainy
season and at high tide, it may be
wider (Ref. 4). During the floods in
August 1986, the mouth was
approximately 40m wide.

In the past the mouth must have been
closed for various lengths of time
(Ref. 1). During times of low flow, the
sandspit is build up to a state of near
closure (Ref. 1). The mouth is
opened during floods, when the
sediments are washed out to sea,
forming an offshore delta, from where
the sand is returned to the sandspit
during calmer conditions.

Although the Gourits River mouth
occasionally forms a double spit, as
was the situation in 1984, the mouth
as a rule consists of an extensive
sandspit on the western side with
rocks lining the eastern shore of the
mouth.



Generally, the topography at the mouth is described as a flat featureless
topography.

In 1981 no man-made obstructions were present in the estuary, which
restrict the flow of water.

A low-level bridge across the river, about 8 km upstream of “Die Eiland”,
was washed away during the floods in 1981. It was replaced by a new,
better constructed bridge, with a higher elevation, further upstream in
1983.
During 1987 a group of riparian land owners constructed an illegal, earth
weir across the river, approximately 1.5 km upstream of “Die Eiland” near
the head of the estuary. The effect of this obstruction was not yet
determined by 1989, but it was suspected that it could cause increased
erosion of the river bed and should the weir be washed away or damaged,
it could result in increased siltation in the estuary below the site of the weir.
It could also alter the water chemistry and result in desalination above the
weir, and increased salinity below the weir, which in turn, could result in
changes in plant and animal communities. The brackish water upstream of
the weir contributes to the increased mineralization of the adjacent
agricultural soil.

Ref.1. Heydorn, H.J. (1989). Estuaries of the Cape. Part II: Synopses of available information on
individual systems. Report No. 38 Gourits (CSW 25). CSIR Report 437, 66pp.
Ref.6. Day, J.H. (1981). Summaries of current knowledge of 43 estuaries in southern Africa. In:
Estuarine ecology with particular reference to southern Africa. J. H. Day (ed.). Cape Town. Balkema:
251-330



Gouritsmond has a moderate climate.
Temperature varies from 6 - 25 degrees Celsius in winter and 10 - 28
degrees Celsius in summer.

Rainfall ranges from less than 200 mm/a to over 1 000 mm/a.
Gouritsmond has an average rainfall of 350mm per year. 57% of this
rainfall falls from April to September.

On average for the whole year, winds are well distributed within the
western, south-western and eastern sectors, with the westerly winds
having the highest frequency of occurrence and highest velocity.

Ref.15. Gouritsmond. General information. http://gouritsmond.co.za/information/frmain.html



A fine balance should be maintained when planning future
developments, such as dams, which could result in a reduction of the
regular scouring of the river mouth by frequent smaller floods.

Invader plants such as Acacia cyclops and Acacia saligna threaten the
environment.

Other threats to the environment are wind erosion, overgrazing and
over utilisation by animals and man, dune moles in cultivated lands,
shortage of trace elements in soils, periodic flooding, brackish soils,
poor quality, limited water for irrigation, low pH and nutrient values of
soils. Wind erosion is aggravated by mineralization and salt
deposition on agricultural lands and consequently results in the lack of
vegetation cover.

Ref.1. Heydorn, H.J. (1989). Estuaries of the Cape. Part II: Synopses of available information on individual
systems. Report No. 38 Gourits (CSW 25). CSIR Report 437, 66pp
Ref.14. Brink, Stokes, Marais and Moolman (1986). Loodsprojek: Kussensitiwiteite, Mosselbaai tot Breërivier.
Saamgestel vir die Departement van Omgewingsake



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