Boston A Dam
Boston A
spillway and
spillway
channel
Botterkloof
Dam spillway
Figure 1: Illustration of the location of the Stortemelk Hydropower Station, as per cover image.
excavations in ‘weak’ material requiring strong supports
to the vertical slopes through a series of anchoring and
shotcrete. The power station had to be built in the narrow
space between the two existing dams, and construction
work had to continue around fully operational infrastructure:
the Botterkloof Dam (owned by the DWS) and the adjacent
privately owned Boston A Dam. Permission had to be
obtained from the respective owners and all regulatory
permits approved before the project could be submitted to
the REIPPP. Another significant challenge in the construction
itself included the need for deep excavations through the
left embankment of the Botterkloof Dam and adjacent to the
spillway stilling basin, while such construction needed to be
done without affecting operations and stability of either of
the two dams. This was aggravated by the high water table,
being in-between two dams that had for effect seepage
during construction and an impact on the ‘buoyancy’ design
(Rochecouste Collet et al., 2016).
The power station design solution was a shallow intake,
followed by a cut and cover concrete penstock, leading to a
compact hydropower station housing a single 4.4MW vertical
Compact Axial Turbine Kaplan turbine ending in the tailrace,
which was rotated at 90 degrees at the draft tube. Two
turbines were considered further, namely the saxo and the
conventional arrangement with a concrete spiral. The saxo
type was eventually selected, as it offered a smaller power
station footprint, reducing civil works, while offering easy
erection and easy access to the runner and guide vanes for
inspections and maintenance purposes.
The Andritz Compact Axial Turbine (CAT) also offers the
benefit that the turbine guide vane is closed by means of
gravity (counterweight). Nevertheless, an emergency gate
connected to the turbine controller is also provided, as guide
vanes jamming remains a risk owing to high vegetation,
although coarse and fine trash racks are provided at the
intake. The generator is cooled by means of a two-circle
closed loop water and air system, with heat exchangers
located in the penstock (Rochecouste Collet et al., 2016).
The successful implementation of the Stortemelk project
has made a noteworthy contribution of renewable energy to
the South African power grid and boosted the local economy.
The Aurecon team is proud of the fact that they have now
34
Water Sewage & Effluent May/June 2017
been part of three successful hydropower stations in the
eastern Free State. This has brought them to the attention of
private sector developers and lenders, and the Aurecon team
is now involved in several hydropower projects across Africa.
In fact, Werner Comrie, unit manager: Water at Aurecon
Tshwane, stated that the hydropower service line is now
one of the fastest growing service lines in this multinational
consultancy company.
The project was also a successful collaboration between
various stakeholders, for which Aurecon and the project
developer would like to thank TCTA, DWS, Eskom, LHWC, and
the landowner, J Farrell, for their enthusiastic support. u
References
Rochecouste Collet, B.J., Blersch, P.C., and Olivier, A.L. (2016).
Design Considerations for the Stortemelk Hydropower Station,
South Africa. Paper presented at ANCOLD 2016.
Van Vuuren, S.J. (2010). A High Level Scoping Investigation
into the Potential of Energy Saving and Production/Generation
in the Supply of Water Through Pressurized Conduits. WRC
Report no. KV238/10.
The successful implementation of
the Stortemelk project has made a
noteworthy contribution of renewable
energy to the South African power grid
and boosted the local economy.
Acknowledgements
The author wants to thank Werner Comrie and Bertrand
Rochecouste Collet at Aurecon for the valuable information
and photos supplied, and their willingness to be
interviewed for this article.