Water, Sewage & Effluent May-June 2017 - Page 35

Lesotho Highlands Water Project ’ s happy spin-off

It is highly gratifying when sound and well-planned mega infrastructure projects have positive and often unplanned spin-offs . By Helgard Muller , Pr Eng

When the Lesotho Highlands Water Project ( LHWP ) was planned , it did include a hydropower component at Muela in Lesotho , but at the time , nobody thought that additional electricity could be generated with the ‘ new water flows ’ from the South African rivers flowing towards the Vaal Dam . The Stortemelk small hydropower plant is such a positive spin-off of the LHWP — relatively small , but with significant implications . The global driving forces behind renewable energy alternatives are environmental as well as energy security concerns . Wind , solar , and hydro all have untapped potential of renewable energy . Renewable energy has made significant strides in South Africa over the past couple of years , with hydropower being the most established and universalised renewable energy technology across the globe . Water from the LHWP is transferred through a gravity tunnel from the Katse Dam in Lesotho into the Ash River near the town of Clarens and eventually lands up in the Vaal Dam . The Ash River was , by origin , a small river until the LHWP discharges augmented the natural flow by almost 500 times to an annual average flow of 24.5m 3 / s . Flows will further increase to approximately 40m 3 / s once Phase II of the LHWP comes fully on stream . To mitigate significant erosion caused by the greatly increased and varying flow , several structures were erected along the river , including the Botterkloof Dam .

The dam comprises a composite structure with a rolled concrete construction ( RCC ) central spillway and earth embankments on the two flanks . It is approximately 17.5m high and is owned by the Department of Water and Sanitation ( DWS ). While watching the energy being dissipated in the dam ’ s spillway — therefore effectively being wasted — a private developer envisaged the idea to harness the same water for power generation . The river also offered rapids some 1.6km downstream , which also showed potential for hydropower generation .
Aurecon conducted the feasibility study in 2010 for both sites on behalf of REH Project Development . The study included the combined options , which concluded that the most optimum solution would be to implement two cascading schemes separately owing to better advantages , such as reduced capital investment , reduced risks , better return on investment , reduced impact on the canoeists who use the river for recreational purposes , and reduced land acquisition .
The upper of the two schemes , the Stortemelk Hydropower Station , is located on the left bank in-between the existing concrete spillway of the Botterkloof Dam and the spillway of the Boston A Dam , as shown in Figure 1 .
Stortemelk Hydro ( Pty ) Ltd , a Special Purpose Vehicle company created solely for the implementation of the project , then submitted a bid ( reverse auction ) to the Department of Energy under Round Two of the Renewable Energy Independent Power Producer Programme ( REIPPP ). After being named a preferred bidder , a Power Purchase Agreement ( PPA ) was signed with Eskom Holdings . The project is financed under a Project Finance with Limited
Helgard Muller
Water , Sewage and Effluent ( WSE ) welcomes Helgard Muller as a regular contributor to this publication . Helgard recently retired from the Department of Water Affairs , where he served as deputy director-general : Policy and Regulations . His vast knowledge in policy and regulations at the Department of Water and Sanitation will add huge value to WSE .
Recourse structure , with 70 % of the debt funded by the Rand Merchant Bank of South Africa and the remaining 30 % funded via equity ( Rochecouste Collet , Blersch & Olivier , 2016 ).
While engaging with the Aurecon team on this project , it became clear that modern hydropower is much more than just ‘ water released from a reservoir that flows through a turbine and spinning it , which in turn activates a generator to produce electricity ’. Scanning through a WRC study ( Van Vuuren , 2010 ), I quickly learnt that there are a few bits more than a dam and a turbine , such as the specific design criteria for water flows into the penstock , different types of turbines , a facility to dissipate the unused or excess energy that is generated , as well as several protection systems .
Aurecon has provided engineering , procurement , and construction management ( EPCM ) services for the entire project . Construction of the 4.4MW hydropower station commenced in September 2014 , and was commissioned ahead of time and under budget . Bertrand Rochecouste Collet , Stortemelk project leader at Aurecon , said , “ It means that the amount provided for contingencies was not even touched and all went as planned .”
According to international definitions , Stortemelk falls into the small hydropower category , because its generation capacity slots in-between 2.3 and 23MW , whereas mini hydropower generated is a facility of less than 2MW , micro hydropower is a facility of less than 300kW , and pico hydropower generated is a really tiny facility of less than 10kW ( Van Vuuren , 2010 ).
The Stortemelk power station was designed to be fully automated , hence unstaffed , with only a caretaker visiting the site daily for routine checks and cleaning purposes . It offers remote access via secure web for all operations and control , as and when required . The design took into consideration comments from operation and maintenance company REH Operation & Maintenance , such as their experience with cooling water filtration systems , and the fact that maintenance can be simplified if all consumables are readily available on the local market and by using universal components .
The site posed a couple of specific geological challenges , such as the low bearing capability of the foundation and deep
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