The Rietvlei stream first flows through the Marais dam that acts
as a sludge or silt dam for the larger dam and joins the Grootvlei
stream that flows through the reserve into the larger Rietvlei Dam.
The wetland running through the reserve is approximately eight
kilometres long and at some places 600 meters wide.
Rietvlei Nature Reserve’s wetlands were identified as
having the potential to sustain peat lands. A major part of the
wetland system consists of peat lands. Peat is a natural organic
resource presently being deposited in certain wetlands in South
Africa. It forms an active part of the filter and storage
capabilities of wetlands and plays a vital role as a water
resource.
Peat forms when plant material, usually in marshy areas, is
inhibited from decaying fully by acidic and anaerobic conditions.
It is composed mainly of marshland vegetation: trees, grasses,
fungi, as well as other types of organic remains, such as insects,
and animal corpses. Under certain conditions, the decomposition of
the latter (in the absence of oxygen) is inhibited, and
archaeologists often take advantage of this.
Peat layer growth and the degree of decomposition (or
humification) depend principally on its composition and on
the degree of water logging. Peat formed in very wet conditions
accumulates considerably faster, and is less decomposed, than that
in drier places. This allows climatologists to use peat as an
indicator of climatic change. The composition of peat can also be
used to reconstruct ancient ecologies by examining the types and
quantities of its organic constituents.
Under the right conditions, peat is the earliest stage in the
formation of coal. Most modern peat bogs formed in high latitudes
after the retreat of the glaciers at the end of the last ice age
some 9,000 years ago. They usually grow slowly, at the rate of
about a millimeter per year.
The peat land in Rietvlei also acts as a natural filter and a
sponge that stores vast quantities of water. Fifty percent of all
the wetlands in the world are peat lands, and most of these are
located in the Northern Hemisphere. Only one percent of all peat
lands occur in Africa and South America, collectively. Peat lands
such as the one in Rietvlei Nature Reserve are thus a rare feature
in the southern African landscape.
The Rietvlei wetland is a valley-bottom fen and the southern
portion (the northern section of Witkoppies) is approximately 77 ha
in extent and before mining commenced, contained up to 1 280 000 m³
of peat with an average thickness of 1.7 meters. As much as 70-90 %
of this southern peatland surface area was mined and portions of
the northern peat land were destroyed by fire. The southern wetland
was severely degraded by the peat mining.
The Central wetland portion is located from the old Witkoppies
boundary to just below the confluence of the Grootvlei tributaries
and Rietvlei stream and is approximately 85 ha in extent. It can be
classified as a seasonal floodplain and seepage wetland. The
Northern peat land stretches from the confluence of the two streams
to the inflow of the Rietvlei Dam and is approximately 70 ha in
extent. It has an average peat thickness of 0.75 meters and
contained up to 525 000 m³ of peat before large portions were lost
in a number of peat fires.
Research identified three plant communities and six
sub-communities with a baseline vegetation survey of rehabilitated
peatland on Rietvlei Nature Reserve. It was noted that the majority
of the pioneer plant species were exotic weeds.
An additional supply of water comes from four natural springs
within the Reserve, a spring on the adjacent private property and
from five boreholes on the dolomite areas in the reserve. The
overflow of subterranean water appears as dolomite springs, which
sometimes produce a strong flow of water. The 5 boreholes on the
reserve have, because of water extraction, unfortunately dropped
the water table and only one of the springs is still supplying a
strong flow. Today the Rietvlei Nature Reserve provides 4.8% of
Pretoria’s water requirements, estimated at 41 million litres
of water per day. The rest of the water used in the city is mainly
bought from Rand Water and the Vaal scheme. One of these pipelines
for water supply runs through the reserve.
Please note the rules on the reserve:
- The public is requested to stay in their vehicles and they are
only allowed to get out at the picnic site and bird hides at their
own risk.
- The speed limit is 30 km/h and some of the roads are closed to
the public mainly because they go to the fences or are inaccessible
with normal vehicles.
- No pets are allowed.
- Fires are only permitted at the picnic sites.
Acknowledgements:
City of Tshwane Agriculture and environmental Management
department.
To qualify for logging this cache, please answer the listed
questions below in a e-mail to the cache owner:
- At waypoint one you will notice a stream on the north side of
the road; what do you think is the source of the water on the south
side of the road? (Please stay in your vehicle and observe the area
to the South of the road)
- From waypoint two you will have a birds eye view of the
wetland; please provide in your mail the difference of reeds and
colours with a estimated height of the reeds.
- At waypoint three you will find a construction that prevents
the wetland from drying out; please provide in your mail what plan
was implemented to prevent the water levels to drop below the
normal wetland water level? (this waypoint is for parking only and
you are requested to stay in your vehicle)