Concern over Lower Berg River water quality
2005-04-07
THE quality of the water quality in the lower Berg River has been a subject of discussion at numerous meetings and workshops over the past two years, due to concern over the future impact of the Berg Water Project.
According to Peter van Niekerk, manager of integrated water resource planning at the Department of Water Affairs, they have managed the quality of water in the lower Berg River on an ongoing basis for more than 30 years and plan measures to ensure that the lower users will not be adversely affected by the Berg Water Project.
Natural flow events of poor water quality occur occasionally during the winter months in the lower Berg River when local runoff takes place from the tributary streams downstream of Voëlvlei Dam.
These streams have catchment areas underlain by geological formations of marine origin containing considerable volumes of salt.
These salts are increasingly mobilised as a result of the changes in agricultural practices, which have occurred in the area, such as deep ploughing and increased irrigation.
Salt concentrations at the Misverstand Dam have on occasion increased above 300mg/l to about 600mg/l for maximum periods of a few weeks.
These salt concentrations might be detrimental to some industries and irrigated crops, although water with similar concentration is supplied to many towns and irrigators in South Africa.
During the summer months good quality water with very low salt concentrations is released into the Berg River from the Theewaterskloof and Voëlvlei Dams.
After the construction of the Berg Water Project, good quality water will be released from the Berg River Dam and from Theewaterskloof Dam, the latter probably at the confluence with the Wemmershoek River below the dam. Therefore there will be no change in the Department’s current arrangements for managing water quality during the summer.
Since the Department commenced releasing water from Theewaterskloof Dam in the early 1970’s to supply irrigators, it has been conducting ongoing investigations into the quality of water in the Berg River in order to better plan and manage the system.
The investigations for the Berg Water Project showed that further water quality studies would be required to plan and manage the water quality at Misverstand Dam, from which Saldanha Steel and Namaqua Sands are supplied, and from which overflows provide the winter water that is pumped into farm dams by a few irrigators.
These investigations will be completed soon to enable the Department to modify its water quality management procedure and/or existing infrastructure.
Farmers in the area have learnt to wait until salt concentrations decrease before filling their dams, van Niekerk added.
Other options which are considered for water consumers dependent on the Misverstand Dam are:
* a pipeline or canal from Voëlvlei Dam to Misverstand Dam;
* temporary damming of the tributaries to the Misverstand Dam;
* moving the pump at Misverstand Dam away from the salty inflow;
* duplicating the existing dam to bridge periods of high salt levels. This second dam already exists and only needs a lining to become functional;
* use groundwater during high salt levels to supply industries dependent on water quality;
* supply additional water volumes to critical industries during salt inflows to decrease pressure on existing desalination plants;
* supply additional desalination plants to critical industries.
The Department of Water Affairs and Forestry is committed to acting responsibly and in the best interests of all its users, van Niekerk said.
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