Water Distribution Strategy

An energy assessment was previously done for a fruit farm in the Western Cape. It was found that 78% of all the electricity consumed was for pumping irrigation water from the water sources to the orchards. This case study is about the follow-on project to optimize the cost of water distribution on the farm.

All the water used for irrigation is from rainfall. The water is collected in 8 buffer dams/reservoirs which is also topped up from 10 boreholes. A network of pumping systems distributes the water from these sources to the orchards, as shown in the diagram below.

 

The cost of water distribution was obtained from the cost of electricity, the energy intensity (kWh/m3) and the flow rate per pumping system. This cost per cubic meter from primary sources to reservoir is given in the graph below. It shows a variation between 50c/m3 and R2.00/m3, with the higher cost water sources clearly indicated.

The same analysis was done for the secondary distribution of water (from reservoir to orchard). In this case the results were normalised to take into effect the differences in pumping heights and pumping distances. The results are shown in the graph below. The variation in cost is between 20c/m3 and 80c/m3.

The final step was to link the primary and secondary chains to obtain the total cost for water distribution to the orchards. This analysis also included the volume of water pumped from each primary and secondary source. The results in the graph below show the total cost per cubic meter for the orchards serviced from the secondary sources. It is clear that there is a huge variation in water distribution cost between the different applications.

These results were then used to develop a water distribution strategy to minimize the total energy cost for water distribution on the farm. The strategy included aspects such as:

  • Using the “correct” amount of water per orchard. Too much water is a waste of energy cost and water, and too little water may reduce the production output of the orchard.
  • Give preference to the lower cost pumping systems for water distribution.
  • Improve the efficiency of higher cost pumping systems and distribution lines.
  • Utilize the lower cost storage dams/reservoirs more than others.
  • Combine electricity supply points to lower the unit cost of electricity.
  • Use solar power solutions to replace the more expensive electricity supply points.