Proposed Upgrading of the Rheenendal Bulk Water Supply, Knysna

The Knysna Municipality intends to upgrade the Rheenendal Bulk Water Supply. The bulk water supply works requires refurbishment/upgrading due to certain equipment/infrastructure not performing adequately and in some instances degradation. Due to the additional capacity required new infrastructure requirements needs to be constructed for future demands.

The objective of the project is to improve the potable water supply and provide adequate clean water storage.

The proposed upgrading/refurbishment works will be undertaken in phases (3 Phases).

This Project (only) focuses on Phase 1, which includes the following Scope of Works

Raw Water Weir
The intention is to repair/fill cracks in the existing weir.

Raw Water Sump at River
A basket type strainer will be installed in the sump so that vegetation can be collected & removed easily. A submersible pump is to be installed in the river with flexible a hose so that during low flows water can be extracted from the river and delivered to the existing delivery raw water sump.

Raw Water Pump Sump
The raw water sump roof slab & chamber walls will be lifted between 0.5m to 1.0m in height so that the alternative borehole pump with additional stages can be installed, as currently the alternative pump is unable to be installed due to the existing depth. The existing electric cable on the outlet of the raw water sump to the control panel is to be protected and secured as it is currently exposed. In addition, gabion structures are proposed to be installed around the pump sump to prevent scour.

Reintroduction of the road
There is a small track path past the raw water sump which is intended to be reintroduced as a roadway. This roadway is approximately 20m in length and will be 3m wide with a 1m wide gabion structure on either side. The total width of the footprint being 5m wide. In addition, the roadway to the existing pumphouse will be graded and re-gravelled. This will all be undertaken within the existing footprint of the roadway.

Pumping Main
The existing bulk water pumping main from the Homtini River to the Water Treatment Works has existing capacity to cater for the current allowable flow from the Homtini River and no upsizing of the pipe is envisaged. New air and non-return valves would be installed where required.

Alternative Raw Water Source Boreholes
Six possible positions for boreholes have been identified, and drilling and equipping of boreholes will be performed once the hydrogeological survey has been conducted. Dependant on the hydrogeological survey completed and the yield of the boreholes once drilling has been completed, pumping mains will be installed from the boreholes to the raw water storage/balancing dam. This will only be known once the boreholes have been drilled, however there is potential for pumping mains to be constructed across drainage courses in the area – these pumping mains will be less than 360mm in diameter.

Raw Water Balancing Dam
The current raw water balancing dam has an approximate storage capacity of 1.5Mℓ. In Phase 1 it is the intention to de-sludge the raw water balancing dam as desludging of the dam has not been undertaken since 2014. To meet future demands an additional 1,5 Mℓ raw water balancing dam is to be constructed to provide additional storage and redundancy – this will be undertaken in the future phases and does not form part of Phase 1.

Raw Water Storage Tank
It is proposed to demolish some of the old WTW (no longer in operation) and remove this and install a 250m³ tank that will be utilised temporarily during the desludging of the raw water balancing dam.