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www.thevillagenews.co.za
12 February 2020
MY ENVIRONMENT
Know the worth of water By Dr Anina Lee
Give your event all the advertising it deserves. It’s FREE! Last year, 135 000 unique readers from 198 countries and territories visited The Village NEWS website (thevillagenews. co.za). So, if you are hosting an event and want to give it some additional free publicity, why don’t you advertise it on What’s On Overberg? It’s easy to use, mobile-friendly and you can even upload pictures!
When the well is dry, we’ll know the worth of water. – Benjamin Franklin
H
ermanus has a long history of searching for water. The first fresh, clear water in the area that is now Hermanus was found by Hermanus Pieters who watered his sheep at a spring just below the present Marine Drive. The first settlers in Hermanus built their homes at a spot west of Hermanuspietersfontein called Rietfontein in the present Westcliff. Again, a source of fresh water was vital to settlement.
Later, the growing town used water from the Onrus River stored in a reservoir near the present Gateway Centre. In the 1930s three dams were built on the Mossel River to supply the needs of the residents. When De Bos Dam was built in 1976 it promised to be the answer to Hermanus’ water needs for many years. At the time, Onrus had sufficient water of its own, but the Hermanus Municipality insisted that this be discontinued and that everyone should buy water from the dam. In truth, it is nothing more than a large farm dam and is now inadequate for the population explosion in Hermanus. The greater Hermanus area now uses approximately 4 to 4.5 million cubic metres (4 to 4.5 billion litres) of water per year.
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Most residents are probably unaware that approximately 30 – 40% of their water (1 to 1.5 million cubic metres) now comes from groundwater. The water is abstracted from 10 (soon to be 12) boreholes spread across three wellfields. These were developed during the first decade of the 21st century. The remainder of the water is supplied by surface water from De Bos Dam. These three wellfields tap into the Peninsula Aquifer of the Table Mountain Group (TMG). Two of the wellfields are situated in the Hemelen-Aarde Valley at Camphill and Volmoed. The third, the Gateway Wellfield, is opposite Gateway Shopping Centre in Hermanus. The rock formations of the TMG create a globally unique groundwater resource. There are two aquifers present below Hermanus. These are not connected to each other in the greater Hermanus area. The upper aquifer (known as the Nardouw Aquifer) is near the surface in the vicinity of Hermanus town centre and is predominantly used by private residents for garden irrigation. The second aquifer (known as the Peninsula Aquifer) is deeper, being approximately 100 – 200 metres deep in the vicinity of the three wellfields. The Overstrand Municipality uses only this aquifer for municipal water supply. However, the water pumped from these boreholes has a high iron and manganese content.
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We are all familiar with the brown colour of local borehole water that is due to red iron oxide leached out of the rocks. The water from the boreholes has to be treated at the Preekstoel Water Treatment Works to remove the iron and manganese. The Municipality makes use of very interesting and effective biological processes to precipitate these metal ions out of the water. But that’s another story.
ABOVE: The De Bos Dam with Die Neus vineyard of Bosman Hermanus in the background. PHOTO: Wines of SA BELOW: The new GWP17 Gateway Wellfield Production Borehole. PHOTO: WCC
Once treated, the water is mixed with water from other sources and further purified for human consumption. In addition to being a welcome water resource to the greater Hermanus area, these aquifers play an important role in the endemic fynbos ecosystems in the mountains around Hermanus. According to Dylan Blake of Umvoto Africa, the Overstrand Municipality uses a world-class, telemetry-based wellfield operational and monitoring system. This system makes it possible to monitor the flow of water and its quality in real time. If at any moment the quality of the water changes negatively, the entire system shuts itself down. It enables the Municipality to withdraw groundwater from the Peninsula Aquifer sustainably, without impacting on important and diverse ecosystems. As environmentally-conscious citizens we are all concerned about the possible effects on Fernkloof and other mountain fynbos refuges of extracting so much groundwater. How do we know when it’s too much? What is the expected lifespan of the boreholes and are there plans to tap other sources of water should the wellfields become unsustainable? Does water abstraction from the Nardouw aquifer by the hundreds of private boreholes in Hermanus affect the water table? Some of the private boreholes are over 100m deep. Are they sucking the ground dry in surrounding gardens? Are they drawing water from the Peninsula Aquifer? A further concern is the ecological health of the Onrus River and its estuary (‘lagoon’) downstream from De Bos Dam. To function properly the river requires adequate water from the dam. Figures published by the Municipality indicate
that the volume of water released from the dam is insufficient to keep the estuary functioning. Can we afford to release more water for the benefit of nature and the people who depend on it? Can we afford not to? For some of these answers, please join Whale Coast Conservation on Tuesday 18 February at 17:30 at the Green House for a talk on Hermanus Hydrogeology. The speaker is Dylan Blake who is an associate and principal geologist at Muizenberg-based earth science and groundwater research consultancy, Umvoto Africa. He has worked on the various Hermanus TMG wellfields since 2007, while Umvoto Africa has been involved with groundwater development in both the Hermanus and Stanford areas since the late 1990s. All are welcome. And remember to celebrate World Water Day on 22nd March every year.
