Area of supply
The Crocodile West River catchment extends northwards from the catchment divide
in central Johannesburg to the Limpopo River. It is characterised by the
sprawling urban and industrial areas of northern Johannesburg and Pretoria,
extensive irrigation downstream of Hartbeespoort Dam, and large mining
developments north of the Magaliesberg.
The Crocodile River has thus been very heavily influenced by human activity.
Noting significant overlap with the Vaal River System, the Crocodile West River
Water Supply System serves a population of about 5.5 million, with over 20% of
the National GDP generated in the Crocodile River catchment.
Sources of water
The water resources that naturally occur in the Crocodile catchment have been
fully developed and utilised. Supplies to northern Johannesburg, Midrand,
Tshwane and environs, are transferred in from the Vaal River via the Rand Water
distribution network. This represents over 45% of the total water use in the
Crocodile catchment, and results in large volumes of return flow (primarily
effluent discharges) from what was originally Vaal River water, being discharged
into the Crocodile River and its tributaries. This, in turn, constitutes an
important source of water for users downstream.
Planning for the future
A water resources study entitled “Development of a Reconciliation Strategy for
the Crocodile West Water Supply System” was completed in 2009. The broad
strategy for the management of water resources with respect to the Crocodile
River System is summarised below:
Water for urban and industrial use in the area south of the Magaliesberg should continue to be supplied predominantly from the Vaal River System via Rand Water. Water for irrigation and rural users should be supplied from local sources.
The bulk of the water available in the area north of the Magaliesberg consists of a combination of local surface resources and return flows. The growth in water requirements in this area will be supplied from the growth in return flows from northern Gauteng, whilst some rural users should continue to be supplied from groundwater.
Large quantities of water need to be transferred to the rapidly developing Lephalale area to augment the local resources. Water for these transfers can mostly be sourced from the Crocodile River by using the surpluses available from return flows in the catchment, but further augmentation from the Vaal River System may also be needed.
Water balance and reconciliation
The light blue shaded portion of the graph accompanying this text presents the
water balance for the whole Crocodile West River catchment for a scenario with
high population growth and medium water demand management. This is the balance
after supplying water to all users within the Crocodile River catchment.
The growing water requirements in the Lephalale area in the Mokolo River
catchment to the north and north-east of the Crocodile River catchment exceed
the available water from the Mokolo River system. Studies are currently being
undertaken by the Department of Water and Sanitation to investigate possible transfer
of surplus water in the Crocodile River system to the Lephalale area
(Mokolo-Crocodile Water Augmentation Project).
There are currently two sets of water requirements for that area, the 2012
Lephalale base demand scenario and the 2012 Lephalale high demand scenario. The
light green and orange lines on the graph below show the net water requirements
for these two scenarios after taking the available yield from the Mokolo River
system into account. It can also be seen that the surplus water in the Crocodile
River catchment, if being considered for transfer to the Lephalale are to meet
the expected shortfall there, is insufficient to supply the total water there.
The green and orange/red areas on the top of the graph above indicate expected
shortages in the Lephalale area after transferring surplus water in the
Crocodile River system to Lephalale. These expected shortages are highlighted in
another way in the graph below.
For the Lephalale base demand scenario shortfalls of up to about 6 million m3/a
can occur between 2022 and 2025. For the Lephalale high demand scenario
shortfalls of up to about 16 million m3/a can occur between 2021 and 2040. The
shortfall is relatively small and temporary. Either infrastructure or demand
side interventions could be considered to achieve a positive water balance.
A Strategy Steering Committee comprising key role players and decision-makers,
was constituted in July 2010. This committee monitors the growth in return
flows, and has regular discussions with developers in the Lephalale area (Eskom,
Sasol, others) regarding requirements, to enable detailed and timeous
adjustments to the Strategy and decisions on further augmentation needs.
BKS and WRP, with support form Golder Associates and Zitholele, were appointed
to manage and execute the project. The contract period for the project is 28
February 2010 – 27 February 2013.