Article

A "model" river runs through it

Judy Bryant

Wachendorfia and other natural vegetation in the water canals running into the Lourens River act as natural filters.

Within the burgeoning urban/industrial area of Somerset West and Strand, a pristine stretch of water is attracting researchers from as far afield as Hamburg University in Germany.

The Lourens River is the only South African river that’s officially a Protected Natural Environment - and dedicated conservation efforts have resulted in its pure waters sustaining a wonderful mix of fish, insects, plants, mammals and micro-organisms.

Ten km of the 20km-long river falls within the historic 300-year-old Somerset West wine estate Vergelegen, which manages the wide variety of ecological treasures in conjunction with the Lourens River Conservation Society, the City of Cape Town and CapeNature.

Vergelegen’s resident conservationist, Gerald Wright, says a number of interventions have contributed to the river’s purity and diversity:
 

• Some 16 million densely packed invasive trees have already been cleared from 1500 ha of the estate in a 10-year, R14m programme that’s currently in its fourth year. This has nurtured the return of natural vegetation and wetlands, while five streams are now flowing strongly for the first time in about 50 years and feeding into the river;
• Water canals running from the high catchment areas on the estate are densely inhabited with natural vegetation such as bullrushes and fragmitis, which act as natural filters;
• The canals lead into attenuation ponds where further settling and filtration takes place;
• The river banks have been cleared of alien vegetation and stabilised;
• The river is encouraged to return to its natural course whenever there is heavy flooding and silting; and
• Vergelegen does not abstract water from the river, although it is legally entitled to take 12.5%; this provides final users, such as Cape Town residents, with larger amounts of cleaner water.
  

The attenuation ponds also fulfil another vital function - they prevent dangerous flooding in the busy Victoria Road section of Somerset West, half a kilometer away. The Lourens River is one of the fastest flowing rivers in South Africa, explains Wright, and a 1/100 flood would speed through Victoria Road at 7m/second if the excess was not contained by the attenuation ponds.

The river contains indigenous fish such as Sandelia capensis and Galaxia spp, while alien trout and carp were released in the past by the river society and others. Shy Cape clawless otters can be seen at night, while marsh mongoose, giant mongoose and Cape grey mongoose live off the fish. Spotted genets also thrive, while resident birdlife includes malachite and giant kingfishers. Wright plans to put down live traps to establish which frog species are present within the water areas at Vergelegen.

Micro-organisms are also closely monitored as they are extremely important for water purity and as a food source for fish, birds and insects such as dragonflies and mayflies. Hamburg University of Technology scientists have researched the water quality, while a third year nature conservation student from the Centre for Agricultural Biodiversity at Stellenbosch University has done work on micro-organisms. Wright intends involving Stellenbosch and Cape University of Technology students in further studies as part of Vergelegen’s Centre of Learning Excellence, which coordinates local and international research into the many conservation interventions at the estate.

“Work on the river is ongoing,” says Wright, as the pristine waters face constant threats. Its estuary near Strand runs past a sewage pump station and raw sewage comes upstream when there are pump problems, destroying micro-organisms. Fertiliser nitrates and phosphates from local golf courses also run into the river; this lingers for a long time and when the river is in a low flow phase, green tendrils can be spotted, indicating the high nutrient level.

Other unwelcome invaders include South American terrapins, which are released into the river by their owners when they grow too large for their tanks. The terrapins thrive on the fish and other organisms.

Despite these challenges, the conservation efforts are winning: Work on the wetland was acknowledged by the prestigious Mail and Guardian 2006 water care merit award, while in the same year the Lourens River Conservation Society presented Vergelegen with an award for work on the river banks.

“We are happy to share our learnings with other interested parties,” says Wright, who conducts environmental walks around the estate for the public. Vergelegen day visitors are free to walk along the river banks and also to view the half-acre wetland garden area that sports gunera, arum lilies, indigenous blue waterlilies and Australis ferns.

More information:

Enquiries: www.vergelegen.co.za / (021) 847-1346 / ladyphillips@vergelegen.co.za  

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