The Department of Water Affairs (DWA) in consultation with stakeholders, is investigating the use of flow manipulation to provide immediate relief from algal blooms along the Vaal River. The current conditions (thick green-blue slime) provides the opportunity to develop and test this approach. This proposed flush discharge, as a potential cyanobacterial (blue-green algae) management strategy, is a first for the Vaal River and a unique opportunity in South Africa.
High levels of algal blooms are appearing along the Vaal River and are currently being experienced within the Vaal Barrage. These algal problems are the result of a combination of too high nutrient loading, warmer temperatures, good sunlight penetration and the lack of variation in river flow over recent weeks. One of the major consequences of eutrophication (nutrient over-enrichment) is the difficulties being experienced when purifying water for potable purposes, due to the water quality problems associated with high algal concentrations in the water.
The Department of Water Affairs has subsequently taken the following steps to address the problem:
- Release water from the Vaal Barrage at 30m3/s on Friday 9 March, followed by 50m3/s on Saturday 10 March.
- Release of 70m3/s for 5 days (Sunday 11 March to Friday 16 March).
- Release water from Vaal Dam at 115m3/s for 3 days (Tuesday 13 March to Friday 16 March).
- Water quality data will be gathered through a monitoring programme to follow changes down-stream in the river. Rand Water, Midvaal Water Company and Sedibeng Water (Bothaville) are also involved.
DWA has already appointed specialists to assist with the field trial. The team of consultants will be responsible for conducting this field study over the next 6 weeks (ending in April 2012). The study will focus on the effect and efficiency of flush flow conditions in the Vaal River on algae, nutrients, pollutants and salts.
The utilisation of flow-manipulation techniques should, however, be regarded as an interim measure until medium and long term measures are in place to reduce the nutrient loads. As a first step toward achieving this, the performance of sewage works discharging to the river system is being addressed as a matter of urgency. Assistance is also being provided to Municipalities where appropriate, to further improve the functioning of sewage works and to increase sewage treatment capacity.
In the longer term the department is planning to establish a nutrient management strategy for the Vaal River that will be aimed at ensuring continued fitness-for-use of the water resources along the Vaal River.
The said strategy may include investigating the use of phosphate-free detergents and investigating the feasibility of introducing stricter phosphate standards in the catchment of the Vaal River.
Please contact:
Linda Page
Tel: 012 336 8250
Cell: 083 460 4482
