SABI/SASOL Watersense

Promoting effective water management practices in the Vaal River catchment

Increasing demand for water as well as below average rainfall during the last season, are putting water resources in the Vaal River catchment under more pressure. As a prominent water user in this catchment, SASOL has stepped forward to promote efficient water use through awareness creation by means of a number of programmes, amongst others the SASOL Water Sense initiative which has won the Water Management category in the 2012 Mail & Guardian “Greening the Future” awards.

In the agricultural water use sector, SASOL has been working with SABI since 2011 to address key aspects of water management at farm level, mainly by presenting farmers’ days and publishing articles on relevant topics.

In order to achieve more focused and measurable outputs, it had been decided to identify a specific area in which to work closely with the water users for the following 2 years, with the aim being to develop and promote efficient water use practices at farm level. The area that was selected is the Sand-Vet WUA near Welkom that also falls within the Vaal River catchment, and the activities that are planned for implementation during the next 2 years include the following:

  • Evaluation of a number of irrigation systems to determine typical application efficiencies and distribution uniformities
  • Provision of irrigation scheduling advice and monitoring services to improve water management practices
  • Regular feedback of project results to the stakeholders  by means of farmers’ days and popular articles

 A dedicated webpage on the Sand-Vet WUA project has been created to present the outcomes and activities as described above.

This web resource aims to broaden the scope of the SABI Sasol initiative started in 2011, by providing information sources and links to technical information that constructively and practically encourage the adoption of effective water management practices at farm level in the irrigation sector.

Technical information is presented in a simple format on topics regarding irrigation design and management, many of them originating during the Farmers Days held in 2011. Feel free to browse the information available.

Links to other relevant websites are provided to put useful information at the water users' finger tips.



The Sand-Vet irrigation scheme south-west of Welkom was selected as it met all the required criteria – the scheme is located within the Vaal River catchment, it has an active WUA, and its Water Management Plan has recently been updated as part of a DWA initiative.

The approach that was taken was to work closely with a selected group of irrigation farmers from the scheme in order to quantify water use and savings as a result of certain (locally relevant) interventions. These results are presented periodically at information days with the aim to build a relationship with irrigation water users in this area, and to generate data that can be used to measure the effects and outcomes of the interventions. The results are also presented to a wider audience by means of articles, posters or other marketing material, such as this webpage.

After the study area had been identified, the following activities were scheduled to take place during the project period:

  • Obtain buy-in and support from the WUA or irrigation board in the selected area.
  • Select a number of irrigation systems or farms where typical irrigation and water management practices can be evaluated.
  • Undertake irrigation system evaluations on the selected systems, analyse the data and use the results to identify typical practices that needs improvement, as well as a smaller number of systems that can be monitored over 1 to 2 seasons.
  • Install monitoring equipment at the selected systems and draw up a monitoring plan.
  • Collect data from the monitoring system and analyse, including weather data.
  • Arrange the first information day in conjunction with the WUA.
  • Continue with monitoring practices over a suitable number of seasons to accommodate the most common types of crops and planting patterns.
  • Schedule regular farmer information days (at least twice per year, after every planting season) to provide feedback to farmers.

The project is in progress, with the first winter season’s monitoring completed and the first summer season’s monitoring currently taking place. Updates of project results are placed periodically on this webpage.

System evaluation results

In order to get a better understanding of the typical efficiency of irrigation systems in the area, a total of 4 systems were evaluated at the start of the 2013 winter planting season, the data analysed and the results communicated to the farmers with suggestions for improvement. A summary of the results is shown below in Table 1.

Table 1   Summary of system evaluation results
Indicator Unit Site 1 Site 2 Site 3 Site 4 Norm
Pivot area: ha 19.1 32.9 42.1 30.1  
Application setting: mm 10.4 20 10 20  
Average applied: mm 7.5 17.1 9.8 18.1  
Uniformity coefficient (CU): % 75.2 86.2 88.7 79.7 >85%
Distribution Uniformity (DU): % 67.3 78.3 78.6 66.3 >75%
Application Efficiency (AE): % 72.4 85.3 98.3 90.3 >80%

The CU (Coefficient of Uniformity) and DU (Distribution Uniformity of the Lower Quarter) are indicators of application uniformity, and only 50% of the systems complied with the required minimum values. Non-compliance of the systems was mostly due to poor maintenance that resulted in leaks and blocked nozzles, which farmers were advised to correct. The AE (application efficiency) is an indicator of the losses that occur between the emitters (sprinklers) and the soil surface and was surprisingly good, meeting the minimum required value in 75% of the cases despite fairly strong winds blowing during the evaluations.

Example of distribution test results and the implications thereof in practice:


Weather data and Scheduling advice

In order to expand the impact of the project and reach a wider audience, involvement at the scheme also entailed the installation of a weather station at the offices of the Sand-Vet WUA. The data from the station is used to generate irrigation scheduling advice for the most commonly planted crops on the scheme, and this information is emailed to all the irrigation farmers on the scheme. An example of the email is shown in Error! Reference source not found..  It contains the historical weather data of the previous 14 days as well as the calculated crop water use for the last 7 days, for the most common crops grown in the area.

Table 2: Example of scheduling advice email


Monitoring results

Monitoring is a very important part of the project, as it is the only way of determining the impact of the activities being undertaken.

From the systems that had been evaluated, 2 systems were selected for site-specific monitoring and scheduling advice during the winter season (2013). A third system was to be monitored but the farmer decided to not plant a winter crop due to the water shortages. During the summer season (2013/2014), probes were installed at 3 sites under maize.  A typical probe installation is shown in Figure 1.

Figure 1  Example of a probe installation in the field

It consists of 2 water content sensors, one for installation in the root zone and the second for installation below the root zone, a data logger for recording data, and a modem for sending the data to a base station operated by the scheduling consultants.

Each farmer receives a daily email and SMS with information on the soil water status and irrigation requirement, together with sickness indexes to manage the crop.  The automated data collection system makes it possible to monitor the irrigation system closely, with only the detail of the irrigation events being required from the farmers.

The first season of monitoring, was winter 2013. Two centre pivots planted with wheat were monitored using soil water content sensors as described above. At the beginning of the season, severe water restrictions were in place, resulting in farmers opting to plant a dryland wheat cultivar in order to minimize the irrigation requirement. Furthermore, they strategically decided to aim for yields between 4 and 6 tons per hectare in order to limit the risk of the harvest in total.

The changes in water content in the root zone as well as the buffer zone for both sites are shown in Figures 2 and 3, and a summary of the measured data shown in the table below:

Table 3  Summary of monitoring results – Winter 2013
  Target yield Measured yield Crop water demand (BEWAB model) Measured application Measured rainfall Measured irrigation (gross)
Ton/ha Ton/ha mm mm mm mm
Site 1 4 1.8 184 177 112 65
Site 2 6 3.9 365 144 112 132

Figure 2 Water content graph for site 1
Figure 3 Water content graph for site 2

In the case of Site 1 (Figure 2), wheat was planted on 30 May 2013 in a deep sandy loam soil with approximately 10% clay. Irrigation was applied twice during the season (September and October) when the buffer zone was depleted and the crop water demand was further supplemented with rain at the end of the season. Because of the long irrigation intervals, roots developed deep into the profile, making it possible for the plants to make use of the water stored in the buffer zone later on in the season, as can be seen in the purple graph.

In the case of site 2, the same cultivar was planted at approximately the same time but in a more sandy soil with a clay layer at approximately 20cm. Smaller amounts of irrigation were applied more often than in the case of Site 1 because of the shallower profile. Although there was more variation in the water content in the root zone during the season, the reaction of the buffer zone was slow compared to Site 1, probably because of the increased clay content and less intensive root development in the deeper parts of the soil profile.

If one considers the results, in the case of Site 1, the yield was 1.8 ton/ha with an irrigation amount of only 65 mm applied over the season, while at Site 2, the yield was 3.9 ton/ha from 132 mm of irrigation. This can be converted to water use productivity values of 2.77 kg per m3 of water for site 1 and 2.95 kg per m3 of water for site 2.  Both farmers reported some yield losses to rodents and birds, especially at site 1.


Contact details

Weervoorspelling / Weather prediction

Riviervloeie / River flows

Analitiese dienste en instrumentasie / Analytical services and instrumentation +

Besproeiingstelsel verskaffers / Irrigation system suppliers

Centre pivots / Spilpunte:

Pumps and motors / Pompe en motors:

Water meters / Watermeters:

For suppliers of other types of irrigation systems, click here

Besproeiingskedulering / Irrigation Scheduling

Besproeiingstelsel evaluasies / Irrigation system evaluations

Navorsingsorganisasies / Research organisations

Internasionale Organisasies / International organisations




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