5 Confirmation of Incremental Approach currently in general use
5.8 RSA Case Study 4: Thukela-Vaal Transfer
This case study examines the appraisal process applied during the investigation into the Thukela-Vaal IBT.
5.8.1 Background
In the early 1990s, as part of the wide ranging study by the (then) DWAF to identify the best options to augment the Vaal River System, called the VAPS, an investigation was conducted at pre-feasibility level into possible transfers from the Thukela River basin to the Vaal River basin. The TVTS would have provided transfers additional to those of the existing
Drakensberg Project, described in paragraph 4.4.1 (DWAF, 1994).
Seventeen possible layouts were analysed in the VAPS-TVTS study. Capital costs and running costs over the design lives of the schemes were discounted to present day costs and their URVs calculated. Four layouts were recommended for further analysis. One of these made use of Eskom‟s Drakensberg pumped storage hydro-electric facility. It involved a large dam on the Thukela River below Spioenkop Dam at a site called the Klip, a dam on the Bushmans River, a tributary of the Thukela at a site called Mielietuin, and conveyance
infrastructure to connect the two proposed dams to the existing Kilburn Dam. The other three options involved new pumped storage facilities, similar to the Drakensberg Project, at sites called Waayhoek and Chatsworth, and therefore were dependent on Eskom‟s interest in (another) such joint project with the department (DWAF, 1994:10-13).
The Thukela Water Project (TWP) feasibility study was a follow-up study of the VAPS TVTS. Apart from identifying the most feasible option, the study was also intended to provide information to allow comparison with the second phase of the LHWP, both projects having been candidates for the next project to augment the Vaal River system.
The economic justification of the project was a primary focus. The preferred scheme comprised the Jana Dam in the main stem of the Thukela River and the Mielietuin Dam on the Bushmans River and aqueducts to transfer 15 m3/s to the existing Drakensberg pump storage scheme as shown in Figure 5-10 (DWAF, 2001c:1).
Figure 5-10: TWP: Proposed Jana and Mielietuin Dams and pipelines to the Drakensberg Project
To compare the TWP proposals with the proposed second phase of the LHWP, a study, called the Vaal River Water Resource Development Project: Comparative Study between
STERKFONTEIN KILBURN WOODSTOCK DRIEL SPIOENKOP QEDUSIZI JANA MIELIETUIN Harrismith Ladysmith Weenen Estcourt Winterton Bergville R23 R23 N3 N3 N3 N3 R49 Pipeline Drakensberg Project Colenso
LHWP II and Thukela Water Project9, was commissioned by the DWA and completed in
2010 (DWA, 2010e).
In the feasibility study it was proposed that the TWP include the following elements: a) The 160m high concrete gravity Jana Dam on the Thukela River with a capacity of
1500 million m3
b) The 97m high concrete arch Mielietuin Dam on the Bushmans River with a capacity of 350 million m3
c) A pumping station at Jana to pump 11 m3/s against a static head of 357m and its 2.5m diameter rising main of 25.6 km
d) A pumping station at Mielietuin to pump 4 m3/s against a static head of 131m and its 1.0m diameter rising main of 19.6 km to meet with the pipeline from Jana
e) Two further pumping stations against a total static head of 234m to convey 15 m3/s to Kilburn Dam by means of a 76.4 km pipeline of diameter varying between 3.0 and 3.1m (DWAF, 2001a:8-1).
The four pumping stations required a combined estimated power supply of 90 MW. To this had to be added the power requirement at the Drakensberg hydroelectric pumped storage plant to convey the water against a static head of 440 m from Kilburn Dam to Sterkfontein Dam.
In the Comparative Study a larger Jana Dam, 190m high with a capacity of 2650 million m3, and with a transfer capability of 12.55 m3/s, was considered for the D3L4High scenario described in the next paragraph.
5.8.2 Summary of the investigation
This section summarises the investigation and its findings.
5.8.2.1 Water requirements and yields
A large number of water requirement scenarios were investigated in a study conducted by the DWAF, called the Reconciliation Study for the Vaal River System. Variables related to the population growth, developments in the Lephalale area, some requiring export from the Vaal River system to the Crocodile-Mokolo system, the re-use of mine water and waste water effluent within the Vaal Supply area, as well as various water conservation and demand management (WC&DM) interventions, brought the total number of possible scenarios in the Reconciliation Study to 96 (DWAF, 2008c:50).
9
The Comparative Study used only four of the demand scenarios; it assumed a 15 % water saving from WC&DM measures, two population growths (high and “base”), and whether the next SASOL CTL plant to be either in the Lephalale area, or below Vaal Dam (DWA,
2010g:3-4).
To balance the demands with supplies from the TWP, different sizes of the two dams, Jana and Mielietuin, were used. The net HFYs, after allowing for the ecological water requirement (EWR), are summarised in Table 5-6 (DWA, 2010e:5).
Table 5-6: Net Yields of TWP dam options
Scheme Dam Size Net HFY (million
m3/a) TWP Jana 840m FSL (small) 293 860m FSL (medium) 325 890m FSL (large) 396 Mielietuin 1015m FSL (small) 112 1025m FSL (medium) 119 1033m FSL (large) 126
The net yields in Table 5-6 were considered the transferable yields from the two dams. These were determined from systems modelling, using the WRYM, during the feasibility study. Stochastic analyses showed that the assurance levels of the HFYs were in the order of 99% (DWAF, 2001a:7-15).
In order to meet the demands, the dams needed to be introduced timeously, taking account of minimum periods of implementation. The Comparative Study used the water balances of six planning scenarios developed in the Reconciliation Study for the Vaal River System involving the TWP. These were developed from simulation modelling analyses of the IVRS using the WRPM (DWAF, 2008c:8).
Figure 5-11 shows one such water balance – the scenario of high population growth, the CTL plant in the Free State and no direct waste water re-use, with identity D3L4High (DWA, 2010g:39). It shows that a large Jana Dam is required by 2018 – the earliest date that it can become operational – followed by a medium Mielietuin Dam later in 2034. It also shows some shortages before 2018, which would require additional measures to deal with, such as some re-use and extra WC&DM measures. This particular scenario, D3L4High, will be used to review the appraisal methodology of this investigation.
Figure 5-11: Vaal River System water balance: Scenario with high population, CTL in the Free State, and no direct waste water re-use (D3L4High)
5.8.2.2 Water transfers
For the D3L4High Scenario in the Comparative Study the annual transfer requirements from the TWP were equated to the projected shortfalls in the Vaal Supply system. The latter were derived by subtracting the system yield from the projected Vaal system demand, capped by the net yield of Jana Dam, as illustrated in Figure 5-12. Detailed figures are provided in ANNEXURE 5-G (DWAF, 2008c:40 and DWA, 2010h:17).
Eradicate unlawful irrigation Deficit due to Jana timeline Deficit due to unlawful irrigation
Figure 5-12: Thukela Vaal: Projected transfers
The Vaal River system yield in Figure 5-12 was equivalent to the total supply capability of the system as determined by simulation analysis, using the WRPM and constrained by applicable curtailment risks (DWAF, 2008:59).
5.8.2.3 Costing
In the Comparative Study the TWP feasibility costs were updated from March 1998 to October 2007. The total capital cost for Jana Dam, pipelines, pumping stations and advance infrastructure came to R10 143 million, as detailed in Table 5-7 (DWA, 2010h:9). This excluded costs associated with Mielietuin Dam, which did not feature further in the comparative analysis as the yield of the Jana Dam was of the same order as that of the second phase of the LHWP (DWA, 2010e:16-17).
Table 5-7: Thukela-Vaal: Capital cost for Scenario D3L4High
Element Civil
R million
M&E R million
Jana Dam at FSL 890 m AMSL 5728.300 322.400
Pipelines - Jana to Kilburn (capacity of 12,55 m3/s) 3425.900 0 Pump stations - Jana to Kilburn
(Capacity 12,55 m3/s) 88.400 395.800 Roads 182.144 0 Total 9424.744 718.200 0 500 1000 1500 2000 2500 3000 3500 4000 2005 2010 2015 2020 2025 2030 2035 2040 2045
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Electricity costs for pumping to Kilburn Dam were assessed at Eskom‟s non-municipal Megaflex electricity charges effective from 1 July 2008. The costs to transfer the water through the Drakensberg pumped storage facility were assessed from Eskom‟s Wholesale Electricity Pricing System (WEPS). For other operating and maintenance costs, standard percentages of capital costs were applied (DWAF, 2010e:19).
5.8.2.4 Economic methodology applied
The URVs for Scenario D3L4High (as for all the other scenarios) were established from the discounted life-cycle cash flows and the water augmentation over a period of 40 years. Real discount rates of 6%, 8% and 10% were used. Capital costs were evenly distributed over five years, starting in 2014. Mechanical and electrical components were replaced after 30 years and residual values were credited at the end of the analysis period, i.e. the year 2058. The electricity cost, at transfer from the TWP of 396 million m3/a, was calculated at R224.14 million/a. This cost was proportioned according to transfer requirements depicted in Figure 5-12 to derive the annual electricity costs for Scenario D3L4High (see ANNEXURE 5-H for detail).
The resultant URVs for Scenario D3L4High are shown in Table 5-8.
Table 5-8: Thukela-Vaal: Derived URVs
Discount rate 6% 8% 10%
URV (R/m3) 3.97 5.31 6.94
5.8.3 Discussion and evaluation
This case study revealed that:
a) The availability of water in the receiving catchment was determined by systems simulation of the IVRS – as it existed at the time. This was called the Vaal River system yield
b) The transferable water from the Thukela River was based on systems analyses of the Thukela System with the inclusion of the proposed scheme, consisting of the Jana and Mielietuin Dams. The HFYs were considered suitable for this purpose as the stochastic hydrological analyses showed the HFYs provide required levels of assurance
c) The projected quantities of water to be transferred annually were assumed to be equal to the shortfalls in the IVRS, i.e. the Vaal River system demands from which
were subtracted the system yield, capped by the yield of the Jana Dam. (The Mielietuin Dam yield was not required for comparison with the second phase of the LHWP.)
d) Pumping costs were derived directly from the quantities to be transferred e) For electricity costs the 2008 Eskom tariffs were used. No shadow pricing was
attempted.
In conclusion: the appraisal approach followed in RSA Case 4 is evaluated against the criteria of paragraph 5.3 as follows:
a) A full system analysis with the inclusion of both the receiving basin and the proposed IBT project was not undertaken. No simulation of annual operations and likely water quantities to be transferred was accordingly performed
b) The assumption was made that all incremental demand, beyond the yield capability of the existing system, had to be supplied from the Thukela System.
It is thus concluded that the approach used in this case study was completely analogous to that of the Incremental Approach described in Chapter 1.