DELPORT DU PREEZ AND ASSOCIATES

CONSULTING ENGINEERS AND PROJECT MANAGERS

Bloemhof dam Flood Monitoring System

A FLOOD MONITORING SYSTEM FOR BLOEMHOF DAM

INDEX:1. Introduction, 2. Background, 3. Purpose of the system, 4. Project planning, 5.Design objectives, 6. Project implementation, 7. Description, 8. Cost and financing, 9.Further developments, 10. Acknowledgements.

1. INTRODUCTION

The Vaal River is one of the most extensively developed river systems in Southern Africa, providing water for domestic and industrial use to most of Gauteng and to some of the largest power stations as well as the Secunda Industrial Complex in Mpumahlanga. In addition a large portion of the available yield is earmarked for agricultural use. The three main dams in the Vaal River System (Grootdraai, Vaal and Bloemhof dams) form the bulk storage facility and should therefore be maintained at maximum capacity. During floods these dams can also be used to buffer the effects of the flood to help contain damage to low-lying property.

A well functioning flow and flood monitoring system is thus considered essential for the efficient operation and management of the Vaal River System.

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2. BACKGROUND

 Since the early years of this century the state had been involved with the monitoring of flow in the Vaal River System in order to determine the sustainable yield. Various machines had been used to monitor flow, with the conventional mechanical chart recorder as the workhorse of the hydrology trade. This system had two distinct disadvantages in that charts had to be collected regularly from site (once per week) and the data was of a historical nature, collected after the event.

 For flood management purposes the Authorities had to rely on information obtained from the Police and from private individuals. These reports were at best very inaccurate and unreliable. For early warning purposes reliance was placed on weather forecasts. The result was poor management of floods with consequent serious loss to lives and property

 In the mid 1970's the Department of Water Affairs an Forestry established a flood control section, making use of Hydrologists and Technicians deployed in the field during flood conditions to relay information to a Control Officer in Pretoria, from where actions were controlled and co-ordinated. This lead to slightly improved control during floods, but the lack of reliable early warning information limited the Department's ability to do flood routing through early release of water at below damage rates from the storage dams. The use of UHF and HF SSB radio communication systems improved control of staff. In the early 1980's a Departmental Committee recommended that an early warning flood monitoring system should be provided to cover the Vaal Dam catchment area.

 DPA designed such a system based on the use of a Land Radio Network and the system was commissioned and handed over in 1986.

During the 1988 floods this system proved its value and allowed the Flood Control Officer to successfully control large floods through the Vaal Dam system without serious loss to property downstream of the Dam. However, the total lack of reliable information on the status of rivers in the catchment of Bloemhof Dam and the Harts River made it impossible for the floods to be safely routed through these dams, with the consequent damage to property and loss of lives. The implementation of a flood monitoring and early warning system for the catchment of Bloemhof Dam was identified as a top priority requirement. Funds were placed on the 5-year capital budget for this purpose. A feasibility report was prepared in 1991 and the instruction to proceed with implementation was given in 1993. The system was commissioned in 1996.

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• 3. PURPOSE OF THE MONITORING SYSTEM

The purpose of the flood monitoring system was defined as:

• Provide constant monitoring of flows in the river and transfer data in near real time to the flood control centre.
• Provide an early warning to the Chief Hydrologist of potentially dangerous conditions in the tributaries of the rivers feeding Bloemhof Dam .

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4. PROJECT PLANNING AND CO-ORDINATION

Employer: Department of Water Affairs and Forestry

 User: Director, Hydrology

 Engineer: Director, Mechanical/Electrical Design

 Specialist Consultant: Delport du Preez and Associates.

 A 12-member project steering committee was formed with representatives from all parties nominated to serve on the committee.

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5. DESIGN OBJECTIVES AND ALTERNATIVES

The design objectives for the flood monitoring system was defined as follows:

• Near real time availability of flow data at the flood control centre in Pretoria.
• Reliable unattended operation with a low maintenance requirement and high rate of availability.
• The creation of the minimum additional infrastructure was desired.
• It should be possible to expand the system to include other dam catchment areas.

 At the time of the feasibility study in 1991/1992 the following alternative systems were available:

• Telkom landlines and Public Switched Telephone Network.
• Terrestrial UHF radio network.
• Long distance radio network.
• Satellite communication system .

 5.1 TELKOM TELEPHONE NETWORK

Although it was remotely considered possible to use the Telkom network, this option was ruled out due to:

Vulnerability of land lines to flood damage

• Unavailability of automatic dialup facilities in the country areas.
• Vulnerability to lightning damage and vandalism.

 5.2 TERRESTRIAL UHF RADIO NETWORK

The successful implementation of the Vaal Dam UHF radio network indicated this method as feasible and economically implementable. This option was however subjected to the following drawbacks:

• Expensive to extend to other catchments
• Requires an extensive network of repeater stations with associated infrastructure (roads, buildings, etc.).

 A radio path analysis indicated that a 7 - repeater station network was required for this system.

5.3 LONG DISTANCE RADIO NETWORK

The difficulties of operating a HF-SSB radio network during adverse whether conditions ruled this option out.

The use of a Meteor Burst VHF radio network was considered a viable option. A pilot Meteor Burst network was established by Delport du Preez and Associates for the Department in 1988, using 10 outstations, as the first such system in Sub-Sahara Africa.

 Extensive evaluation of the pilot network indicated that this option was feasible for providing RSA wide coverage using 2 master station positions.

The only significant drawback of this technology was that there was only one manufacturer in the world, located in the USA.

5.4 SATELLITE COMMUNICATIONS

 In principle two methods were available as communication medium for the flood monitoring system: Private point-to-point links on a time share basis using INMARSAT channels or one-way transmission using the Meteosat data transmission facilities.

 At the time of the feasibility study South Africa was a suspended member of the World Meteorological Organisation (WMO) and was barred from using the Meteosat facilities. The transmission cost to use INMARSAT facilities was extremely high, payable in US $, which would have placed a serious economical burden on the operating budget.

 As there was divided opinions amongst the Employer's staff as to which system should be used, the Consulting Engineers recommended to the Employer to test the comparative costs of the three available technologies on the basis of open tender. A tender document was therefore compiled with three developed designs for an UHF land based radio network, a Meteor Burst system and a satellite communication system. This additional service was rendered at no extra cost to the client.

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6. PROJECT IMPLEMENTATION

Tenders were called for the required services through the State Tender Board. Tender offers were received on 12 February 1994.

The Department undertook all civil works for the project from the Regional Director's offices.

 On adjudication it was found that the Meteosat option was the most economical solution, with the land based radio network as the most expensive due to the civil cost component to develop radio repeater station sites. Access to the Meteosat facilities was however a problem.

A breakthrough came in June 1994 when South-Africa's rights were restored at the WMO.

In November 1993 the WMO published a document in which the establishment of the World Hydrological Cycle Observation System (WHYCOS) was muted. Under this system it was proposed that 100 meteosat DCP stations be deployed in Africa to assist with the collection of Hydrological data for World Bank Planning purposes. When approached, the WMO indicated that South Africa would be allowed access, which would mean satellite transmission facilities at no charge.

In August 1994 the State Tender Board approved the contract award for a system based on Meteosat. An order was placed with the South African contractor Prodesign (Pty) Ltd with Meteosat equipment sourced from Space Technology Systems (UK) Ltd. On 22 December 1994 Eumetsat, the operator of the Meteosat satellite system, granted South Africa the first 20 licences.

In January 1995 another 26 stations to a total of 46 stations extended the network. Factory acceptance of the meteosat equipment took place at the end of February 1995, at a place called Alton (close to Stonehenge on the Salisbury Plains in England).

At a meeting with WMO officials in Geneva in February 1995 it was determined that no WHYCOS protocol existed and it was agreed that a protocol with be defined by South-Africa, based on the Synop FM 12 code system.

On 13 December 1995 the Department obtained beneficial use of the first 10 stations with final commissioning of the 20 Phase 0 stations on 8 May 1996. The 26 Phase 1 stations were accepted on 1 July 1996.

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7. DESCRIPTION OF THE METEOSAT DATA TRANSFER SYSTEM AS IMPLEMENTED FOR THE BLOEMHOF DAM FLOOD MONITORING SYSTEM

The meteosat transmission network consists of a number of components:

• Transducers to collect measurement information.
• Data logger to record information and compile code messages
• Data collection platform (DCP) for transmission to the satellite in the 402MHz band.
• Meteosat in geostationary orbit (0 ° latt, 0 ° long).
• Earth station in Darmstadt in Germany where data is disseminated and retransmitted to users via Meteosat or linked to the GTS network of WMO.
• Data receiving stations (DRS) for direct reception of the satellite signal at 1694,5MHz.
• Data processing

 (* these components are operated by Eumetsat)

7.1 MASTER STATIONS

The network developed for the Department of Water Affairs was configured to allow access to the data to all the parties engaged with the collection of hydrological data and flood control. A network of Base stations equipped with DRS units was established with stations at:

The Flood Control office in Pretoria.

• The Regional Director's office in Bloemfontein.
• The area Manager's office at Jan Kempdorp.
• The Central Electronic Workshops at Standerton (maintenance).

 Further base stations were linked to the network via dial-up modems on the Telkom Public Switched Telephone Network and were located at:

Bloemhof Dam Administration office.

• The Regional Director's office in Centurion.
• The master station at Vaal Dam was upgraded and linked into the network.

With this network all data will be available to the operator at any of the stations. Should the DRS equipment at a station fail that station will be able to extract missing data from any other station in the network via the Telkom facilities.

Each master station comprises of the following modules:

1,8 meter diameter dish antenna

• Low noise amplifier (1 600MHz)
• Down converter to 136MHz
• DRS receiver
• Received data processor
• Operator's processor with decoding software system
• Printer

At the flood control centre the operator's processor provided data download to the flood control processor and into the Department's LAN so that data could be accessed from any connected terminal. The Pretoria and Bloemfontein master stations were further equipped with telephone alarm dial-up-systems to alert the duty Hydrologist, should disturbing data be detected in the system.

7.2 OUTSTATIONS

LOCATION

The original 20 outstations were located at the following sites for collection of data:

Bloemhof Dam

Bloemhof Weir

Valsch at Lindley

Sand at Allemanskraal Dam

Vaal at Klipplaatdrift

Vaal at Orkney

Renoster at Arriesrust

Valsch at Theronsburg

Vaal at Schoemansdrift

Vaal at Goosebay Canyon

Vet at Erfenis Dam

Valsch at Bothaville

Vet at Port Allen

Sand at Bloudrift

Rietspruit at Kaallplaats

Renoster at Koppiesdam

 Rainfall stations were located at:

Wolwekop (Wolmaranstad)

Bulskop (Ventersdorp)

Excelsior (Brandfort)

Naval (Senekal)

The outstations covered an area of approximately 37 500 square km.

EQUIPMENT

The outstation installation consists of the following units:

Transducers for measurement of level and rainfall

• Lightning protection system
• Data logger with a 30 day memory buffer
• Data transmission equipment
• Mast with antenna (10dB forward gain)
• Solar power supply unit with 4 day battery backup

The outstation logger is configured to accept all the inputs as defined in the WHYCOS proposals, including level, rainfall, pH, conductivity, turbidity, solar radiation, air temperature, humidity and TDS.

 The civil woks required to house and/or support the equipment at each outstation was provided by the Department and consisted of:

Equipment hut, manufactured from precast panels, and assembled on site

• Mast base
• Sleeves and pipes for transducer cables
• Transducer mounting units

TYPICAL RIVER MEASURING STATION

7.3 TRANSMISSION CHANNEL

 The meteosat system is primarily intended to provide the National Meteorological Offices with the satellite weather images (WEFAX). Transmission of these images takes up the bulk of the satellite transmission times. Telemetry data is an add-on service, slotted into the gaps between the WEFAX transmissions.

 The transmissions from the DCP units are time and channel allocated, which means data transfer is from earth to satellite only.

 Accurate time and frequency control at the DCP is critical as transmissions outside the allocated time slot and channel will invariably destroy data transmission from other stations.

 All telemetry data to be transferred via Meteosat must comply with WMO formulated codes.

7.4 EXTENSION PHASE OUTSTATIONS

The 26 Phase 1 outstations were located at:

Limpopo at Beit Bridge

Levubu at Mhinga

Letaba at Letaba Range

Olifants at Mamba

Krokodil at Kalkheuwel

Krokodil at Nooitgedacht

Caldon at Ficksburg

Caledon at Wilgedraai

Vaal at Schmittsdrift

Riet at Soutpans

Modder at Glen

Mostert Canal at Virginia

Kornet at Maghalleen

Orange at Oranjedraai

Tugela at Tugela Ferry

Tugela at Mandini

Mzimkulu at The Banks

Pongola at Mhlati

Klip at Ladysmith

Mhlatuze River

Mzimvubu at Inungi

Komati at Komatipoort

Komati at Tonga

Komati at Hooggenoeg

Sabie at Krugergate

Krokodil at Riverside

With the Phase 1 extension the network now covers all the major rivers in the Free State, Kwazulu/Natal, Northern, North West and Mphumalanga Provinces, A further master station with DRS equipment was placed at the Regional Director's office in Durban.

TYPICAL DCP UNIT

TYPICAL DRS UNIT

7.5 RIVER LEVEL (GAUGE) MEASUREMENT

Measurement of flow was done through the measurement of water level and then converting level to flow using algorithms developed by the Hydrologists. These values can only be confirmed by calibration during floods. At some locations the topography of the riverbank was such that cables, sleeves and transducers could not be mounted at the low flow levels. Measuring weirs were not available at all sites. In two instances radar level sensing equipment had to be mounted on road bridges.

7.6 FLOODING OF EQUIPMENT

 Although an attempt was made to place equipment buildings above the 200-year flood line there was no guarantee that the equipment would never be flooded. Special tripping devices had to be installed to remove all electrical power from the equipment during flooding to limit damage.

7.7 EQUIPMENT HOUSING

The outstation equipment was seriously exposed to vandalism in the remote areas. At the start of the contract the type of protective structure required and the construction logistics were analysed. It was concluded that the most effective route was to construct an equipment room using precast concrete panels, to be assembled on site. Two teams were used, no 1 constructing the foundation and mast footings with the second team welding the frames/panels together and bolt the assembled structure to the plinths. Initially this appeared to work well but soon after installation it was noted that equipment malfunctioning was experience during the days. This was traced to excessive temperature, quickly corrected by painting the outside with a light paint colour.

7.8 DATA LOSS AND RECOVERY

The satellite message is structured in such a way that a measurement is only transmitted once. Failure anywhere in the system means data is lost and can not be re-transmitted.

 Special software was developed to allow for data recovery through one of the following means:

• If the failure was a specific DRS unit, data could automatically be recovered from one of the other receiving stations via the Telkom network.
• If the failure was in the Earth-Satellite link, data had to be manually collected from the outstation and then fed into one of the master stations. All other masters will then automatically be updated.

The project was finance by the state through the Department of Water Affairs and Forestry.

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9. FURTHER DEVELOPMENTS

In addition to flood monitoring, the system is now also used for hydrological data collection.

The Department of Water Affairs and Forestry received the appointment from WMO to function as the Regional WHYCOS administrator for the SADC region. This means that the Pretoria master station will in future be linked to the WMO Global Transmission System (GTS) so that all received data can be accessed from all over the world.

 It was also decided by WMO that the message structure must be recorded into a new "open" structure code "CREX" to make it move universally applicable. The new code will be implemented in1998.

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10. ACKNOWLEDGEMENTS

The participation of the following persons in the successful implementation of this project is acknowledged.

Mr. RA Chantler - Chief Engineer (Mechanical/Electrical) and his staff

Mr. S van Biljon - Director: Hydrology and his staff

Mr. AG Visser - Deputy Director: Free State Region and his staff responsible for civil and construction works

Mr. P Cherry - Director Prodesign (Pty) Ltd and staff

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Page prepared by P. D. du Preez. Pr Eng.

©-1997,1998, 2001. DPA CC