Case Study SA-EM7
HYDROGENERATORS IN THE WESTERN AQUEDUCT
Pipes being laid from Midmar Dam through Pietermaritzburg – this will eventually feed onto the
Western Aqueduct.
The type of pipes that will be used in construction of the Western Aqueduct
HYDROGENERATORS IN THE WESTERN AQUEDUCT
Unprecedented growth in water demand in the western supply areas of Ethekwini Metropolitan,
Durban has brought about the need for a new bulk supply pipeline. The opportunity for electricity
generation in this pipeline is an add-on to the project as the primary objective is ensuring an
adequate water supply, but significant savings are anticipated once the project has been
completed.
Background:
The Durban area has experienced a significant increase in water demand in its western supply area over the
past few years, leading to infrastructure capacity problems with the existing distribution system. The
problem has been further aggravated by migrations to the area just west of the greater Durban area, which
are also serviced by this system. The Western Aqueduct supplies an extensive area including northern areas
such as KwaMashu and Inanda, as well as the western areas of Durban North and Umhlanga as well as the
King Shaka Airport.
At present the raw water
supply for the Western
Aqueduct is Inanda Dam,
but many of the areas, for
example Inanda, the airport
and KwaMashu are at
higher elevations than
Inanda Dam. This means
that water is being drained
from a lower point to
provide water at higher
elevations, resulting in
increased pumping costs.
Inanda Dam
The new Western Aqueduct will be supplied from the Midmar Dam which is much higher up in the Umgeni
catchment (at an elevation of over 1000m as opposed to between 200 and 400m for the areas supplied), so
the new aqueduct provided the option of not only saving energy in pumping costs, but also of generating
electricity in the aqueduct.
However, it needs to be stressed that the motivation for construction of the new Western Aqueduct has
been for security of water supply and that energy savings and energy generation are both secondary issues
in the project. For some years now construction of an impoundment, Springrove Dam, on the Umkomaas
River, which is in a separate catchment from that of the Umgeni catchment has been considered, the main
purpose of this impoundment to provide adequate water for the greater Durban area in the future.
Unfortunately Ethekwini Metropolitan is not responsible for the feasibility study of Springrove Dam and
since it has been delayed, the Metropolitan, facing the problem of an ageing and increasingly inadequate
distribution system, were forced to make a decision in what is effectively an information void. Phase I of the
project will rely on water supplied from the Midmar Dam, with Phase II involving augmentation of the
supply from the Springrove Dam, although at this stage, construction of the dam is not certain. Should
Springrove Dam not prove feasible and construction of the dam not go ahead, security of water supply to
the Western Aqueduct may be in jeopardy. However based on present estimates, under the existing
conditions the aqueduct will remain viable until 2030, and even using very conservative figures, the payback
period has been calculated as 12 years, but is expected to be much less than this.
Midmar Dam
The first tender process had been completed in 2011 and based on this the project was scheduled for
completion by July 2013, however a recent high court ruling has resulted in the tender process being
repeated from the beginning again and this will now delay completion of the project until 2016 and will
obviously impact on the payback period as well.
Electricity generation that the scheme will be capable of producing is very dependent on the security of
water supply. Increases in demand on Midmar Dam could lead to a reduction in the water flow in the
aqueduct, which would have a negative impact on electricity generation. The current estimates have been
based on augmentation of the supply from Springrove Dam, but if construction of this dam does not go
ahead, then Ethekwini Metropolitan may have to consider installing smaller generators as there will not be
sufficient water to generate the amount of electricity estimated in the original calculations.
Description of Process:
The new Western Aqueduct, like the present system, will supply the western and northern areas of the
greater Durban area, including KwaMashu, Inanda, Durban North, Umhlanga and the King Shaka Airport.
The new aqueduct will add up to 400 ML/d to the city’s present consumption of 860 ML/d, the additional
water being obtained from Midmar Dam in phase I of the project, while the balance will be obtained
through augmentation from the as yet unconstructed Springrove Dam on the Umkomaas River.
Potential Interventions

Generation of electricity will be carried out by a Public Private Partnership in which Ethekwini
Metropolitan will purchase the generators, but the cost of all other equipment and all the costs of
operation and maintenance will be borne by the private partner.

The private company will be assured of a market for the electricity generated through a 20 or 30 year
contract with Ethekwini Metropolitan which will include the selling of electricity to Durban Electricity, a
subsidiary of Ethekwini Municipality.

The generation of electricity must never take precedence over the supply of water and must not
negatively influence the cost of water to the rate payers.
Range of potential Savings
The feasibility studies were based on a cost of R0.50c/KW, which is the current cost of the electricity
purchased by Durban Electricity from Eskom, the national electricity supplier. The loan required to purchase
and install two generators of 2.7MW each was amortized over a period of 12 years using an interest rate of
8.5%, and based on this the running costs for the 12 year payback period were calculated at R0.31c/KW, so
the system will be financially viable. However, a major concern is still the availability of water since failure to
construct the Springrove Dam and upstream water demands exceeding those used in the feasibility study
would result in reduced flow through the Western Aqueduct. This in turn would have a negative effect on the
generators. Various situations have been modeled in an attempt to assess the impact of different flow rates
in the aqueduct on electricity generation and although the pressure increases that occur in pipelines when
flow rates drop compensate the effects to some degree, if the flow rate drops below a critical volume, the
2.7 MW generators would be too large to work effectively.
Case Study SA-EM7
HYDROGENERATORS IN THE WESTERN AQUEDUCT
Ref
Case Study SA-EM7
Response information, description and remarks
1
Location:
Ethekwini Metropolitan, Durban, South Africa.
Urban population and the generators would be positioned at two sites
with the system.
2
Sector:
Clean water
3
Works Owner or Operator:
Ethekwini Metropolitan will own the Western Aqueduct, but the electricity
generation project would be done on a Public Private Partnership basis, with
Ethekwini constructing the aqueduct and the private partner purchasing the
generators and associated equipment and taking responsibility for operation
and maintenance of the system. This would be through a 20 to 30 year
contract in which the private partner would be assured of a market for the
generated electricity.
4
Size:
Based on current estimations the Western Aqueduct will eventually convey in
the region of 1260 ML/d water. The Western Aqueduct in its present form
transports around 860 ML/d. However, the flows at each generator site will
be different. At the first site, Ashley Drive the flows will initially be 100 to 230
ML/d, but once water from Springrove Dam comes on line, the flows are
expected to be around 330 ML/d. The second site is at Wyebank and the
flows here will initially be between 50 and 190 ML/d, but is expected to
increase to around 280 ML/d once Springrove Dam comes on line.
If the Springrove Dam is not constructed, then according to the worst case
scenario, the flow volume in the aqueduct will steadily decrease to zero by
2038.
5
Energy Provider:
The project will result in a net production of electrical energy. At present
water is pumped in some areas by as high as 150m. Once construction of
the new Western Aqueduct is complete and two generators each rated at 2.7
MW have been installed, not only will the pumping costs be greatly reduced,
but electricity will also be generated. At present electricity is purchased from
Durban Electricity, which in turn purchases electricity from Eskom, the
national electricity agency. Electricity costs have increased significantly over
the past few years and even greater increases are anticipated over the next
7 to 10 years. In addition intermittent power outages have occurred over the
past few years due to demand exceeding supply.
6
Process:
The project would involve the installation of 2 hydro generators, so this is a
physical process only.
7
Component:
The project involves only part of the distribution system.
8
Motivation for the case study:
Energy generation was not the primary motivation for the overall project. The
main motivator was that the water supply to the Western Aqueduct is
diminishing as a result of both an increase in demand and diminishing water
supplies available for areas lower in the catchment. A secondary problem
was of energy wasted in pumping to higher elevations. Thirdly the current
infrastructure is inadequate for the projected water demands. The opportunity
for energy generation was realized and has been included into the overall
project.
Process/Plant changes:
Two 2.7 MW hydro generators would be installed into the new Western
Aqueduct, together with transformers and the relevant electrical fittings and
controls.
9
10
Civil/Physical Changes:
Civil changes would be minima and would include the housing and pipes
required by the generators. The generators would not have any impact on
the water quality or the distribution system.
11
Operational Changes:
The project would be carried out through a Public Private Partnership
agreement with the Private Partner being responsible for operation and
maintenance of the generators. In other words, the Private partner would
need to ensure that their employees have the necessary skills, but there
would be no additional skills required by Ethekwini Metropolitan.
Ethekwini Metropolitan has only recently started to become “generator
friendly”, so this project is one a number that are being considered at
present that will affect the way that the municipality conducts its business.
12
Risks and Dependencies:
The greatest threat to the project is an inadequate water supply. If
Springrove Dam is not constructed and or water demand on Midmar Dam
exceeds expectations, the resultant decrease in volumes through the
aqueduct would impact negatively on electricity generation
An additional threat which has more relevance to the aqueduct than to the
electricity generation project is that of water management. The traditional
and conservative method of water management dictates that water should
remain as high in the catchment for as long as possible, whereas in order
for this project to be successful and to ensure adequate electricity
generation, water will be stored for longer periods at lower, rather than
higher, elevation in the catchment.
13
Implementation:
The construction of the Western Aqueduct is not at the tender stage yet, but
is scheduled for completion by 2016. The electrical generator project will be
implemented in terms of a public private partnership signed for a period of
between 20 and 30 years. The private partner will purchase all equipment,
operate and maintain the system and in terms of the PPP sell all electricity
generated to Ethekwini Municipality.
14
Energy Efficiency gains:
Based on the feasibility study that includes Springrove Dam in the
calculations, two generators each rated at 2.7 MW each will be installed at
two separate sites in the Western Aqueduct. The feasibility study indicates
that there will be sufficient water to operate these generators until 2030,
even if Springrove Dam is not built. Therefore based on the period from
2016 (scheduled completion date of the aqueduct and installation of the
generators) to 2030 and two generators each rated at 2.7 MW, the total
electrical energy generated will be 662256 MWh,
Figures are not available for the amount of energy presently used in
pumping water from Inanda Dam to an elevation of some 150m above the
dam, but the energy saved in this way will be in addition to that generated in
the aqueduct.
15
Cost / Benefit analysis:
Based on the current cost of electricity purchased from Eskom of R0.50c/KW
and using interest rates of 8.5%, the payback period has been calculated as
12 years. Factoring in these figures (i.e. 12 year amortization at 8.5%), the
running cost of electricity generation has been calculated at R0.31c/KW.
16
Project review:
This project is still in the feasibility stage.
17
Confidence grade:
Although the project has not been completed, or even implemented, the
technology is proven and the confidence level that it will be successful is
fairly high until at least 2030.