WATER SUPPLY TO FARMERS
Originally this system was operated on the turn system whereby the farmers within the zone are listed in sequence and the determined stream would supply the Irrigators according to that sequence for the number of hours he is entitled to dependant on the area of the farm that is scheduled.
This was a situation of either the Irrigator had to take the water or forfeit the supply, because of this system the Irrigator was forced to construct a dam at great expense so as to place him in a better situation for the utilization of his water. These factors limited the types of crops that could be planted.
During the mid 80's it was felt that a better system could be developed with the utilisation of computer technology, which eventually resulted in what is known as the Request System.
Some background as to how water is supplied to the Irrigators;
1. There is approximately 20 164,5 ha scheduled in the valley.
2. The area is divided into some 112 zones. A zone is a group of Irrigators that are geographically adjacent to each other and have a determined stream size supplying that specific zone.
3. There is nearly 1 094 delivery points.
For the system to operate logically the Irrigators are arranged in a specific sequence within the zone and all the streams required in a specific week are added together and the water is let into the canal system as per the description in the request system below.
Other factors that influence the supply of water, which must be accounted for by the Board in its calculations, are;
1. Transit time
Time taken for the water to be taken from the source to the delivery point, which will also be affected by the volume that is required ie high volume shorter time and vice versa low volume longer time.
2. Expected losses in the system.
This aspect must be considered so that sufficient water is taken into the canal system to avoid any shortages so that the required volume of water can be supplied to the Irrigator.
3. Capacities of the Balancing dams.
This is very important especially when the decision must be made as to when Darlington Dam must be opened, as it could have the result that insufficient water will be flowing in the canal.
In the event that there is insufficient balancing capacity and Darlington Dam is not opened early enough, there will not be any water to deliver to the Irrigator. Transit time from Darlington Dam to Korhaans Weir at the head of the canal system is between 24 to 38 hours dependent on the release flow rate.
A problem experienced is the right prediction of all these elements in the calculation of water requirements as a lot of the information is obtained by physical observations and varies from week to week.