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Rehabilitation and Restoration of Thesen Islands'Ornamental Ponds

It has been a long, hard road to get to the point we're at today. So long and hard that we'd love to share the story to date with our Homeowners. At the time of writing, work is still underway so we will continue to publish a series of articles until the project is fully completed.

Thanks to the efforts of a handful of passionate Islanders, water is once again flowing in our parkland ponds, and birds are making a reappearance only a day after we filled them. Egyptian Geese (naturally!), Blacksmith Lapwings, Grey Herons, a Pied Kingfisher, and even a pair of Water Thick-Knees are already testing the new waters. There are also crabs and frog's spawn in the ponds.

Pivotal to the story of the ponds' demise is the relentless drought of 2016/2017. In 2007 Knysna's annual rainfall sat at 1,500 mm (the 20-year average is 916 mm). During the drought, rainfall plummeted to a pitiful 370 mm. Slowly, over the years, things have improved and as 2020 closes we are standing at 634 mm. Our biggest challenge is still water retention; historically much of it was being lost through seepage.

 
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Shrunken Ponds 1 & 2 after the prolonged drought of 2016/2017

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A third layer, Bidim cloth, was laid over the HDPE, akin to a soggy blanket which helps bind the soil thus enabling plants to grow and which also protects the waterproof liner from UV light.

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One of the two fountains which forms part of the closed recirculating water system between Ponds 1, 2 and 3.

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Bidim cloth laid at Pond 3

 
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The journey to pond restoration took massive collaboration between many parties: a small Thesen Islands task team, Barloworld and their environmental consultants, the Dept. of Environment, Forestry & Fisheries, Knysna Municipality, and SANParks. After an initial expensive rehabilitation proposal, the T.I. task team concluded that they could undertake and manage the project themselves cost-effectively. The team eventually halved the cost of rehabilitation.

 

Our solution included lining the ponds with a waterproof layer to prevent ground seepage, and making the new ponds both smaller and shallower to limit water volume as well as solar evaporation. The overall pond area is now about 2,300 sq. metres, reduced from about 3,000 sq. metres.

 

The first process involved laying down metre-wide strips of a corrugated plastic to enable the venting of any gaseous ground release. The second layer was a 1 mm thick HDPE (high density polyethylene) watertight layer; the polyethylene has a 10-year warranty.

 

 With the approval of the Knysna Municipality, the ponds have been filled with municipal water using a fire hydrant running at low volume across three days. It took approximately a million litres of water to fill Ponds 1, 2 and 3. The ingenuity of the rehabilitation process lies in its closed recirculating water system. Pond 1, when seen from above has two arms to it, with a fountain in each component. Water flows from the fountains into the pond, and it then cascades underneath a little walkable bridge (still to be installed) into Pond 2, and then into Pond 3 via pipes beneath the paved road. A pump in Pond 3 redirects water back into Pond 2, and from there it is pumped up to Pond 1, flowing up through the fountains to begin the process once again.

 
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The target is to complete the work by the 15th December. The final planting, however, will be undertaken over the course of a season, maybe two. The T.I. task team also enlisted the support of a respected horticulturalist from the Pledge Nature Reserve as well as an expert from the Lakes Bird Club. The Club is affiliated to BirdLife SA. Turfworx, as our appointed landscaping contractor, will propagate additional plants in our nursery, which will then need a season to establish themselves.

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The quoted cost for the restoration of the ponds was R5,5 million but the works are predicted to come in under a third of that. Funds were drawn from the Capital & Maintenance budget; no extra levies from our Homeowners are necessary. There will inevitably be some water loss from the ponds through evaporation but the volume, and hence the cost, will be limited.

As for Pond 4 (the dried-up extensive reedbeds near the bird hide and beyond), work on this area will be undertaken next year. Environmental work is for Barloworld's account. The stand of black wattles in the reedbeds is presently a nesting site for Black-headed Herons and Sacred Ibises so, for now, the wattles have been ring-barked and are to be removed once the breeding season is over.

We intend to publish an update to this article on the completion of the pond rehabilitation.

 
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Thank you to Elfrieda Loubser and Renette Kumm for the use of their photographs