Background to the Project
The existing GBWSS has experienced water restrictions since 2014 due to the inability of the existing infrastructure to supply the growth in water demand.
Various studies have been undertaken by VCWB, MMM and DWS to identify options to augment the supply to the GBWSS.
The 2012 Reconciliation Strategy identified the following major interventions:
Implementation of water conservation and water demand management,
Increase capacity of Tienfontein pump station,
Implementation of the Welbedacht / Knellpoort bi-directional pipeline, and,
Implementation of re-use of treated effluent.
Other recommendations from the 2012 Reconciliation Strategy include:
Addressing the siltation problems at Welbedacht WTW to increase the operating capacity of the plant,
Improving the integrity of the Welbedacht pipeline, and,
Increasing the capacity of the Maselspoort WTW and raise Mockes Dam.
The above interventions and recommendations were considered the most economical options that can be implemented in the shortest possible timeframes.
The 2012 Reconciliation Strategy also identified the transfer to water from Gariep Dam as the next augmentation scheme to be considered after implementation of the above interventions.
MMM and VCWB both investigated the transfer of water from Gariep Dam and came to different conclusions on the preferred solution, i.e.:
MMM concluded that a direct pipeline from Gariep Dam to Bloemfontein, conveying potable water, will be the optimal solution, and,
VCWB concluded that a pipeline from Gariep Dam to Knellpoort Dam, conveying raw water, will be the optimal solution.
As a result, DWS decided to initiate this study, referred to as the “Greater Mangaung Water Augmentation Project – Xhariep Pipeline Feasibility Study”.
The purpose of this study is to appraise, at a pre-feasibility level of detail, the most promising previously identified development options (routes) for the Xhariep Pipeline Project and to recommend the optimal system size (including phasing) and the best water conveyance route from a regional and national perspective that should be taken forward to the feasibility stages of study.
The three most feasible pipeline route options identified from previous studies were:
Scheme 1: Direct potable pipeline from Gariep Dam to Bloemfontein,
Scheme 2: Raw water pipeline from Gariep Dam to Knellpoort Dam, and
Scheme 3: Raw water pipeline from Gariep Dam to the Novo Outfall Structures.
A fourth scheme, referred to as Scheme 4, was identified at the commencement of this study.
Scheme 4 is a raw water pipeline from Gariep Dam to Rustfontein Dam, which aims to reduce the losses associated with Scheme 3 where water will be conveyed along the upper reaches of the Modder River before being discharged into Rustfontein Dam.
The pipeline routes for the four schemes are shown in Figure 2.
Figure 2: All four routes investigated in the Xhariep Pipeline Feasibility Study
Study Methodology
Feasibility studies are iterative in nature as interventions/schemes are required such that the water resources yield matches the forecasted water demands, followed by infrastructure option identification,
refinement of the yield modelling, refinement of the infrastructure sizing, etc. This iterative process, and the steps followed for this study, is shown in Figure 3
In this study, the Xhariep Pipeline infrastructure was integrated into the existing GBWSS infrastructure. Different schemes could offer varying historic firm yields due to system losses, such as water conveyance along the Modder River.
These yield differences affected the volumes transferred to meet 2050 water demands, impacting infrastructure sizing, capital, and operating costs. Another variable was the yield required from Gariep Dam to meet 2050 demands, initially estimated at 60 million m3/a. Further yield modelling would be conducted if this volume proved insufficient to satisfy the 2050 demands.
Figure 3 shows a flow chart of the process followed to determine the optimal scheme to be taken forward as part of the detailed feasibility study phase.
The following assumptions were made in the development of the process flow chart:
The volume to be transferred from Gariep Dam to meet the 2050 demands will exceed 60 million m3/a, which will require further water resources modelling, and
An alternative to the preferred potable water and raw water schemes might be required to satisfy the overall objectives of the study. This alternative is referred to as a “hybrid” option.
The following definitions were applied with respect to the schemes/options considered:
Scheme/Option – this refers to the four main schemes/options being considered as shown in Figure 2, and
Sub-Option – for each scheme/option, multiple sub-options were developed to consider alternative locations of booster pump stations, reservoirs, and different pipeline sizes.
It is evident from Figure 3 that an iterative process had to be followed between the water resources analysis and infrastructure sizing. The process also included stakeholder engagement at key points in the project to present progress and findings, and to provide an opportunity for stakeholders to comment on the proposed solution(s).
Figure 3: Methodology for the Xhariep Pipeline Feasibility Study
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