As technology improved it was felt that this could be used to improve service delivery, limit canal losses but also control the overtime costs experienced with the manual system. This system required the installation of Rotork Actuators on the sluices and ultra sonic sensors to monitor the flow in the canals and overseen by an out-station, which includes a CPU and radio at each of the identified points.
It was decided that nine stations would be automated being the most critical in the control of the system. At each of these points the data is fed into the out-station and transmits this information to the central station while controlling the adjustments to the rotorks mounted on the sluice gates as instructed by the central station to maintain the correct canal flow.
This information is transmitted telemetrically (radio) to the central computer in the Main Office of the Association from where the overall control and monitoring of the canal system is done.
The readings and times are calculated as explained under the Request System and are input into the central computer, which then transmits these readings to the various stations.
Alarms are included in this system, which will indicate that imminent problems may arise or are being experienced.
HOW IS WATER SUPPLIED FROM THE ORANGE RIVER?
Water is withdrawn from the Gariep Dam at Oviston through the Teebus tunnel, which discharges, into the Teebus River, which flows into the Great Fish River.
At the Elandsdrift Dam, approximately 15 kms downstream of Cradock, the water is diverted into a canal, which flows through the Cookhouse tunnel and discharges into the Little Fish River near Somerset East.
The water flows approximately four kilometres to the De Mistkraal Weir, where the water is lifted approximately four metres into a canal, which discharges into the Skoenmakers River, which flows into Darlington Dam.
The De Mistkraal weir replaced the Wellington Grove pump station, which was in operation from 1978 until 1987. Construction of the De Mistkraal weir commenced in 1984 and was constructed using the method of Rollcrete.
From Darlington Dam the Association controls the releases.
Due to the distance involved from the Gariep Dam to Darlington Dam the Department developed a computer model, which also takes into consideration the quality of the water that is required in Darlington Dam and arranges the releases from Oviston accordingly.
DEVELOPMENT OF THE CANAL SYSTEM
During 1985 the Department of Water Affairs decided to upgrade the Main canal as well as rerouting the canal, which would include additional ground for agricultural development. This development would expand the area under irrigation to approximately 20 000 ha but due to financial restrictions the area was curtailed to approximately 16 000 ha.
These works were completed at the end of 1993 and the area between Barkley Bridge and Colchester will be completed at some future date and is included in the Orange River Replanning Study completed in 1999.