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News // The Hidden Hydrology of Groenvlei, Western Cape, South Africa

Date // 23rd September 2014

The Hidden Hydrology of Groenvlei, Western Cape, South Africa

Peter Penning, Antea Group, discusses the hidden hydrology of lake Groenvlei in South Africa.

"Inogen consultant conferred with Doctor of Philosophy by Institute of Groundwater studies for research carried out on hydrology of Groenclei, South Africa."

The Institute of Groundwater Studies, University of the Free State conferred a Doctor of Philosophy degree on well-known South African hydrogeologist and Inogen consultant Roger Parsons for his research on the hydrology of Groenvlei, a shallow brackish lake near Sedgefield, South Africa. The lake is very close to Goukamma Nature Reserve. He undertook the research in response to a growing need to better understand surface – groundwater interactions. "Eight of the twenty one wetlands in South Africa designated as wetlands of international importance are found in similar geohydrological settings as Groenvlei" said Parsons. "By studying the simplest of them, I was able to debunk misconceptions about the role of groundwater sustaining such wetlands".

"During winter, the reeds are dormant and do not transpire any water, but in summer the reeds pump out between 10% and 30% more than that evaporated from the open water body."

From the research it was concluded reeds around the lake play an important role in controlling both evapotranspiration losses and the salinity of the wetland. During winter, the reeds are dormant and do not transpire any water, but in summer the reeds pump out between 10% and 30% more than that evaporated from the open water body. Rainfall and groundwater are key drivers of  the wetland, and no surface flows discharge into or out of Groenvlei.

The lake formed about 6000 years ago, with the estuarine character of an early Groenvlei evident from the presence of relict estuarine fauna in the lake. The daily water balance model developed during the research was used to show that the lake rapidly readjusted once disconnected from the sea, taking about 120 years to reflect control of the new hydrological and chemistry drivers.

An improved knowledge of the hydrology of wetlands like Groenvlei is critical if the systems are to be better managed and protected, as dictated by South Africa's water law.

For more information on South Africa, water stewardship or this research please contact Peter Penning,  peter.penning@anteagroup.com.

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