THE sustainability of South Africa’s water systems demands a careful balance between human water needs and the ecological health of our rivers.
Kerry Grimmer, a principal hydrologist at SRK Consulting, highlights the significance of considering ecological water requirements (EWRs), which are fundamental to responsible water management.
“The ‘reserve’, as outlined in South Africa’s National Water Act, is designed to ensure that water is allocated not just for human consumption but also to sustain the health of our aquatic ecosystems,” she explains. “The reserve comprises two components: the basic human needs reserve, which ensures essential water supply for people, and the ecological reserve, which maintains the integrity of river systems.”
She emphasises the importance of incorporating EWRs into hydrological models, ensuring that water projects do not compromise the health of rivers.
Natural flow
“When SRK assesses water resources for projects, we take into account the needs of existing downstream users,” she says. “We also recognise that, if we don’t protect the natural flow and quality of our water systems, we risk long-term degradation of the river.”
She highlights that water management demands a fair distribution of water between human consumption (domestic water supply), agricultural irrigation, mining and industry, and environmental conservation. If too much water is extracted, the consequences could include loss of biodiversity and habitat destruction.
In addition, the return water into a river system can result in poor water quality, especially when coupled with unnaturally decreased river flows. This can be caused by applying fertilizer to irrigation water, for example, which can be washed into the river system or seep into the groundwater. Non-compliant return water from a water treatment plant could also compromise water quality.
SRK’s methodology includes determining how much water must remain in a river to support its natural ecosystem.
Long-term health of rivers
“This is especially important when assessing the yield of a dam or a water supply system,” she continues. “The more water allocated to the EWR, the less is available for allocation to users. However, this sacrifice is necessary to preserve the long-term health of our rivers.”
Different river systems and catchments require varying levels of EWRs, depending on their condition. They are therefore classified on a scale from Class A, which represents pristine conditions, to Class E, which indicates severe degradation.
Using the Desktop Reserve Model developed by Professor Denis Hughes and Rhodes University, SRK determines the appropriate EWRs for different river systems.
“The calculations take into account natural flow patterns, which are the flows that would occur without any man-made impacts,” she explains. “Our goal is to mimic natural conditions as closely as possible, ensuring that our rivers continue to function as healthy ecosystems.”
For more information: https://www.srk.com/
