FOSAF NEWS - Rondegat alien fish project: Status report

1. Upgrading of lower Rondegat River weir

The lower Rondegat River weir was damaged in an extreme flooding event in 2008 and a side channel also formed next to the existing barrier.

It was decided to upgrade the weir to make it an effective fish barrier and with the cooperation of the Department of Water Affairs a gabion structure was designed for the upgrading. The plan was drawn up by Mr. Harry Swart of the Department of Water Affairs in Paarl. The upgrading of the weir is a listed activity in terms of National Environmental Management Act (Act No. 107 of 1998). Footprint Environmental Services were contracted to do the environmental impact assessment. The Environmental Authorization was granted on 14 June 2012 (Ref. No. E12/2/4/1-F2/2-2003/12) by the Department of Environmental Affairs and Development Planning (DEADP). In October 2012 invitations for quotations for the upgrading of the weir were advertised and on 16 October 2012 a site briefing session were held at the weir with prospective contractors. The upgrading of the weir should be completed by the end of January 2013. Riaan van der Walt will serve as the Environmental Control Officer (ECO) during the upgrading of the weir. The second piscicide treatment will take place after the weir upgrade is completed.

2. Fish rescue

From 23 to 25 October 2012 Dr Olaf Weyl from the South African Institute of Aquatic Biodiversity (SAIAB) will lead a fish survey of the Rondegat River that will include snorkel surveys of the treatment zone. This survey should give an indication of the indigenous fish that have moved down into the treatment zone and the effort needed to re-locate them by way of a fish rescue before the second treatment is undertaken.

3. Second rotenone treatment

The major change from the first treatment will be the reduction of CFT Legumine from 1.0 to 0.75 ppm. For the second treatment, only four drip stations will be used spaced over the treatment zone as recommended by Dr Brian Finlayson. The de-activation station during the first treatment was just below the lower weir but for the second treatment it will be placed about 200 m below the weir. A small waterfall barrier at this point below the weir could provide a secondary safeguard against alien fish getting past the upgraded lower weir. The deactivation station will dispense Potassium Permanganate at 5ppm to neutralise the rotenone and will run for 24 hours.

The actual date of the second treatment has not been finalized but will be either February or March 2013.

4. Biological Monitoring Report

A comprehensive report entitled “Monitoring the impact and recovery of the biota of the Rondegat River after the removal of alien fishes” has been prepared by Woodford et. al for the Water Research Commission. Once the report is approved for publication, interested YWG members can contact the WRC to obtain a copy.

19 October 2012
Riaan van der Walt
Technical Co-ordinator, AVM Fauna, CapeNature
rvanderwalt@capenature.co.za

 

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