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Enquiries: Mr M. Matlala/LZ Maswuma
Telephone: 012-336-7860
Reference: 2/1/5/1
MINISTER OF WATER AND ENVIRONMENTAL AFFAIRS
NATIONAL ASSEMBLY: QUESTION 158 FOR WRITTEN REPLY
A draft reply to the above-mentioned question asked by Mr G R Morgan (DA);
is attached for your consideration.
Attached is a letter to the Member, Mr G R Morgan for your signature.
DIRECTOR-GENERAL (Acting)
DATE:
DRAFT REPLY APPROVED/AMENDED
MRS B E E MOLEWA, MP
MINISTER OF WATER AND ENVIRONMENTAL AFFAIRS
DATE:
NATIONAL ASSEMBLY
FOR WRITTEN REPLY
QUESTION NO 158
DATE OF PUBLICATION IN INTERNAL QUESTION PAPER: 10 FEBRUARY 2011
(INTERNAL QUESTION PAPER NO. 01)
158. Mr G R Morgan (DA) to ask the Minister of Water and Environmental
Affairs:
(1) With reference to the Vaal Dam hydrograph for the period 30
December 2010 to 20Â January 2011 (details furnished), why was
the dam on 30 December 2010 already permitted to be over 100%
capacity when weather forecasts at the time predicted the
likelihood of increased rainfall in the period going forward;
(2) why was the capacity of the dam permitted to exceed 102% between
1 January 2011 and 3 January 2011 without any adjustment in the
outflow from the dam;
(3) why was the rapid escalation in outflow from the dam that was
permitted between 5Â January 2011 and 7 January 2011 not started
earlier in order to reduce the peak of the outflow;
(4) what are the (a) names and (b) designations of all persons
involved in the management of the percentage capacity of the dam
during the above period;
(5) whether she was personally briefed by her officials during the
above periods on (a) the changing percentage capacity of the dam
and (b) the management of the outflow during this period; if
not, why not; if so, what are the relevant details?
NW171E
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REPLY:
The âmanagementâ of floods in the Vaal/Orange River system is
carried out in terms of a Technical Guide which is the result of
more than 30 years of hands on action, experience and
development in the flood management and flood forecasting of the
Vaa/Orange River System a very large catchment, half the size of
South Africa.
This Guide combines existing institutional memory and experience
into a document which is used during a flood event and also to
develop and train knowledgeable people in order to enable flood
managers to correctly apply the basic principles of flood
management without much practical experience of the real
situation. During a flood event the Flood Management Office
collects substantial real time and forecasted data which is
processed, analysed and fed into the flood routing system to
enable the Flood Management Personnel to make decisions on
releases of water from those dams which have controlled
spillways and also to provide the Disaster Management Centers
(National and Provincial) with accurate information regarding
the stage of the river system.
The training and development of knowledgeable hydrologists,
technicians and engineers in flood management takes many years
mainly for 2 reasons:
⢠It takes 10 years or longer to know and understand the
behavior of each river and flow gauging stations in the
catchments. This will enable the person to distinguish
between correct and incorrect real time data vital for
immediate decision making during a crisis situation.
⢠To solve a hypothetical flood routing problem during training
in office differs very much from the real world situation.
Training in the real world situation does not happen
frequently, for example since 1988 there have only been 4
major floods experienced (1988, 1996, 2010 and 2011).
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The main objectives of flood management are:
1. Ensuring the safety of the structure and therefore human
life;
2. Minimisation of damage. (The emphasis will be on optimal
utilisation of dams and rivers in the system to reduce peak
flows and not necessarily on the optimum operation of each
dam individually); and
3. Ensuring that the dams are 100% full at the end of the flood
event.
River flow in South Africa is monitored with the help of various
telemetry systems receiving flow and rainfall data from more
than 450 gauging stations. The data is transmitted from the
different flow gauging stations via different communication
links, including satellite, to the Flood Management Room in
Pretoria and the Disaster Recovery Center at Vaal Dam. The real
time flow and stage data is then used as input to the flood
routing model.
The maintenance of the South African Real Time Data System is a
major task. Skilled hydrologists, technicians and engineers are
used for maintaining the hard and software of the system. During
flood situations a wide network of both people and technology is
put into action. The crucial first step is the gathering of
accurate information about rainfall and runoff in the catchment
areas of the rivers and the storage levels and inflows into
dams.
Rainfall / Runoff prediction models are used mainly during the
period just after the rainfall event before runoff reaches the
gauging stations in the rivers.
This gives an early indication of expected flows and volumes
that will reach the dams. Rainfall, weather patterns and
forecasts are regularly monitored to get a clear picture of what
has happened up to now (rainfall), what is happening now
(present rainfall areas and intensities by monitoring satellite
images and radar) and what will happen in the next few days
(short and medium term weather forecast).
(1) Previous experiences have taught that it would be
irresponsible to act on weather forecasts alone as they
serve to place the Department on alert. The Department
reacts on measured rainfall and flows observed at flow
gauging weirs in our rivers. This gives a safe window of
between two and three days before the water reaches the
Vaal Dam.
(2) The Vaal dam is one of a number of major dams in the
Vaal/Orange River systems which are managed as part of the
system during a regional flood event as experienced in
January 2011. Decisions are therefore based on the state of
the entire system (all dams as well as the stage of the
rivers) during such a flood event and not on a single dam
in the system. The Vaal cannot therefore be analysed on its
own without taking into account the stage of the rivers as
well as the state of the other dams in the system.
(3) Falls away.
(4)(a) There are eight officials who are responsible for
flood management in the flood management room (details
furnished).
(4)(b) The team comprise of the following:
â Two Chief Engineers;
â Three Specialist Engineers;
â Two Production Scientists (Hydrologists); and
â One Senior Software Developer.
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(5)(a) Yes, from 24 December 2010 I was kept informed on a
daily basis. On 06 January 2011 I visited both the flood
management room as well as the Vaal Dam and on 10 January
2011; I conducted an inspection of the Vaal River as far as
the confluence with the Orange River at Douglas.
(5)(b) Yes, information regarding the management of the
outflow was communicated to me by the management team of
the Department on a daily basis
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