coaltech upper olifants river catchment wetland inventory ...

3.4.3 Pans
Pans are sometimes difficult to define (Allan et al 1995, Morant 1983). Endorheic pans are
typically circular to oval shallow depressions without an outflow. Pans are seldom more than
three meters deep, although systems up to 20m deep have been defined as pans. Some
systems in Mpumalanga that are large, deep and permanently wet can be defined either as
pans or as lakes. In addition, pans have been viewed as a lake type in the past (Allan et al
1995).
The classification of pans in South Africa has various problems and is mostly based on the
function of the classification system. A classification system proposed by Noble and Hemens
in 1978 classified pans on the physical characteristics of the pans, as well as the fauna and
flora species composition. The pans were classified as, salt, temporary, grass, sedge, reed
and semi-permanent pans. Other classification systems also focussed on the duration of
inundation (Allan et al 1995, Geldenhuys 1982). Pans in the UORC cannot be sub-divided
into different wetland types, since too little information of pans in the catchment is currently
available to attempt this.
Pans are normally distributed in the dry part of the country, but a number of pans also occur
in the wetter portions of the country, including the UORC. Pans are also distributed across
various vegetation biomes, including grassland, the vegetation biome present in the UORC.
The distribution of pans across the world is generally affected by four abiotic factors. These
factors are bedrock, drainage, slope and climate. Climatic conditions normally associated
with the formation of pans are low mean annual rainfall (lower than 500mm) and high mean
annual evaporation loss (higher than 1 000mm). A good example of an exception to this rule
is the pans in the UORC, an area with annual rainfall of approximately 700mm (Allan et al
1995).
The formation of pans is complex and can be influenced by climate, geology, surfaces,
disturbance by animals, lack of integrated drainage systems and wind. The collection of
water in the pans contributes to the enlargement of the pans. When pans dry out in the dry
season the area is bare of vegetation. The loss of sediment takes place through the action of
wind. The pans therefore, become deeper and larger and the round shape of the pans is
caused by the swirling action of winds. Animals trample the edges of the pans thereby
loosening the soil and carrying mud away from the pan (Allan et al 1995, Goudie & Thomas
1985).
Wetland Database for UORC - 32 -