Area covered: > 100 000 ha under irrigation

Water saved: 500 – 1000 m³/ha/y depending on fruit tree species.

South Africa is a major producer of various types of fruit all of which are grown under irrigation. Yet the country is ranked as one of the driest receiving less than half the global average annual rainfall. The sustainability and growth of the fruit industry requires innovative and practical solutions to cope with the increasing demand for the scarce water resources. Access to water for irrigation in South Africa has historically been skewed in favour of large established commercial farms. The South African Water Act of 1998 attempts to address this inequity by implementing Water Allocation Reforms (WAR) so that all growers have access to adequate water to ensure sustainable production.

To facilitate the implementation of the water allocation reforms in a pilot catchment in north-eastern South Africa, a decision support system (DSS) was developed and tested on irrigated tree crops. The DSS is based on the internationally acclaimed FAO 56 principles wherein crop water requirements are calculated as the product of the reference evapotranspiration and a crop coefficient (Kc). In the DSS, the entire study area is split into small water management units called quaternary catchments. A 50-year record of daily climate data is placed at the centroid of each quaternary catchment to account for the variation in climate conditions across the study area and between years.

The novelty of the DSS resides in the approach developed to calculate the crop coefficients which are the main source of uncertainty for the FAO 56 methodology. The Kc estimation approach, first proposed by Allen and Pereira (2006) uses readily available data such as average tree height, and the fractional vegetation cover. This approach worked well for annual crops, but not for tree crops due to differences in the aerodynamic properties of trees. In our DSS we proposed a novel approach to estimate the Kc values for a range of subtropical tree crops. Details of the proposed methodology are published in the Agricultural Water Management journal on the following link.    
https://www.sciencedirect.com/science/article/pii/S0378377423002548  

The DSS was validated extensively using actual orchard transpiration measured using sap flow techniques and whole orchard evapotranspiration measured using the open path eddy covariance systems. The DSS has facilitated discussions between irrigators and catchment management agency officials around a user-friendly tool that outputs:

1. reliable estimates of the crop water requirements for subtropical tree crops (mango, litchi, grapefruit, citrus, banana, sugarcane)
2. reliable estimates of the maximum yield based on the transpiration reduction due to water stress
3. estimates of the water use efficiency of the crops across the catchment, and;
4. transferable crop coefficients based on the specific situation of the individual field.

The DSS exists in the form of a web-based platform on the link below. The link shows the map of the IUWMA area and farm boundaries to allow users to navigate to their specific farms. 

 http://mapcropfactorsapp.s3-website.af-south-1.amazonaws.com/  

The DSS generates accurate crop coefficients using readily available data considering the characteristics of each orchard (e.g. crop type, canopy cover, irrigation system, soil type etc.). This information is being used for improving irrigation scheduling through accurate estimates of crop water requirements. The DSS is also being used to make decisions on water relocation within the catchment to ensure equitable access to water. The tool is readily accessible on smartphones, and computers by various users.     

Stakeholder engagements and training sessions have been planned for the catchment to disseminate and to encourage uptake of the tool.

It may be roll out across the entire country as the need for water allocation reforms are national in character. There is need to increase the amount of crops that are covered in the DSS.

Dr. Sebinasi Dzikiti played a key role in developing the Decision Support System (DSS) for water use efficiency in irrigated tree crops.

He was the lead author of the report and contributed significantly to the scientific foundation of the DSS. His expertise in horticultural science and water resource management helped shape the system’s ability to optimize irrigation strategies.

The 4th BPWA was presented to the Working Group on On-Farm Irrigation Systems (WG-ON-FARM) by the President Dr. Gao Zhanyi on the occasion of the 65th IEC and 22nd ICID Congress held at Gwangju, Republic of Korea, September 2014. The performance of a workbody is adjudged based upon a set of criteria and its contribution towards the mandate and mission of ICID.

The Award was presented to Vice President Hon. Felix B. Reinders (South Africa), Chairman, WG-ON-FARM.

South African National Committee on Irrigation and Drainage (SANCID) has won the 4th BPNC Award. The award was received by VPH Felix Britz Reinders from President Chandra Madramootoo on the occasion of the 62nd IEC and 21st ICID Congress held at Tehran, Iran, October 2011.

In South Africa, the major rivers are already over-extended, and irrigation uses about 60% of the total water supply; good planning and management of irrigation water are of utter importance to increase the efficiency of irrigation water use. Irrigation water managers required an easy-to-use planning tool to estimate water requirements and enable the supply of the right amount of water at the right time.

A user-friendly computer model was developed that enabled irrigation water users to plan the amount of irrigation water required by an irrigation farm, an irrigation scheme, or a water management area monthly. This tool, SAPWAT, was a further development of CROPWAT and is being used by more than 300 users in 13 countries, even though it was designed against the background of South African needs. SAPWAT 3 the latest version of the computer model is not a crop growth model. It is designed to allow the user to imitate through interaction the situation in an irrigated field. This allows the user to do “what if” with different irrigation scenarios to see what the effect of a specific management decision is on irrigation water requirements. Some characteristics are as follows:

Data Management: The program has the facility of data management including big data sets, the data is stored on board for easy access and addresses the limitations of web accessibility. CLIMWAT, CROPWAT weather data have been included along with daily data of 5,100 weather stations. Daily data for any number of successive years is used to do year-on-year irrigation requirement estimates, the result of which allows the user to include risk analysis as part of the planning process.

Crops: 104 crops are included in the crops data now expanded to 2,500 crop records by providing for differences in growth and development because of different planting types at different times of the year and in different climates.

Salinity stress and water stress situations can be imitated. This module works from two sides. The effect of stress on yield is displayed, or the user can also define a level of yield reduction to stretch the water need. If yield reduction is defined, the program will apply water stress so that yield reduction reflects the required level.

All irrigation requirement estimates can be stored and revisited to determine what effect changes in irrigation water management, irrigation system and changes in planting dates could have.

The editing functions of weather stations allow the user to adapt data to represent predicted climate change scenarios which can be used to predict irrigation water requirements under climate change situations. “Now-then what-if” scenarios could be set.

Data can be exported for use in other applications such as for use in spreadsheets. A module for small (back-yard) water harvesting situations where the amount of water required for a small garden can be estimated. Runoff from roof and/or adjacent hard-packed surfaces and storage requirements are determined. Maximum garden size for balance with harvest area and storage is calculated. Pumping times with low technology pumps such as the treadle pump is also calculated. Large data sets can safely be handled. The weather data amounts to about 38 million records.

SAPWAT3 Model: The program provides the user with the ability to manage all the background data that is used by SAPWAT3. These include crops, irrigation systems, soils, area water distribution systems, weather stations, enterprise budgets, countries, and an address list. Köppen climate definitions are also given, but these are read-only. The user does an area, farm, field, crop set-up to reflect the area of work. Provision is made for back-wards summation of crop irrigation requirement to field, farm, and area irrigation requirement. The efficiencies of irrigation water reticulation systems at different levels are included in this calculation.

The crop for which irrigation requirement needs to be estimated is defined in terms of weather stations and climate, soil type, irrigation system, planting date, foliage cover, yield, area planted, and irrigation management strategy. For year-on-year irrigation requirement estimates, subsets of the weather data, such as a period that is known to have had a below-average rainfall, can be selected.

The results are graphically displayed as crop coefficient, evaporation, and crop evapotranspiration as well as soil water content over the growing season.

Further results show monthly and total irrigation water required for different levels of non-exceedance, as well as levels of efficiency of irrigation water use and rainfall use efficiency. Daily water balances can be inspected, specifically for identifying water stress situations.

SAPWAT3 is used by irrigation designers in South Africa to optimize water use to its fullest extent. One such case is short grower maize planted on 15 December. If the irrigation strategy is to make the best possible use of rainfall by not filling the soil profile to field capacity during irrigation, the irrigation water required is 320 mm. If the irrigation strategy is changed to always fill the soil profile to field capacity, which results in low rainfall use efficiency, the irrigation requirement is 500 mm. Irrigation water-saving by using the better strategy amounts to 180 mm, or 36%. If this saving is translated to the 1.5 Mha irrigated in South Africa, total annual irrigation water-saving could amount to 27,000 MCM.

The SAPWAT3 has been fully endorsed by the Department of Water Affairs in South Africa as a tool to issue water licenses for irrigation purposes. A survey amongst users about one year after publication shows that 51% found it a useful tool and that 46% found it easy to use. Apart from application in South Africa, SAPWAT3 has been used in Angola, Mali, Mozambique, Namibia, Niger, Swaziland, and Uzbekistan for irrigation system design and irrigation water use planning.

The Vaalharts irrigation scheme is situated at the confluence of the Harts and Vaal rivers on the border between the North West and the Northern Cape provinces in South Africa. It is the largest irrigation scheme in the country, with a scheduled area of 29,181 ha. The scheme consists of a network of canals covering a distance of more than 100 km supplying water to about 1,873 abstraction points through pressure regulating sluices.

Vaalharts water distribution practices suffered from the limitations of a manual system including higher labour force requirements, calculation/estimation errors, indirect method of estimation of releases, difficulty in incorporating the changes in demand, individual’s experience, and information collation in the distribution management making the water use efficiency reports time consuming and inaccurate.

The weekly water distribution management practices at Vaalharts Water were very labour-intensive. Moreover, preventing water losses and maintaining a good rapport with farmers was becoming increasingly difficult for the management.  These limitations were overcome by developing and introducing a computerized system in the form of the Water Administration System (WAS).

Water orders were captured directly by water control officers, calculation errors were eliminated, water balances were updated daily, conventional charts were replaced by digitized systems, and release volumes were computed weekly instead of earlier monthly volumes. The water distribution sheets were modified quickly incorporating the changes in the demand and water use efficiency reports were generated automatically with the WAS. The computer system facilitated the water control officers to carry out more inspections and minor repairs like canal leakages and breakages which were easily monitored while maintaining a timeline for clients.

Productivity vastly improved with reliable water use efficiency reports produced using WAS. The water control officers developed a positive attitude as their administrative responsibilities were reduced and they could invest more time in strategic planning. Water losses on the scheme decreased from 32% to 26.7% in a single year due to WAS’s efficient mechanisms.

The implementation of the WAS program made water-savings at Vaalharts Irrigation scheme sustainable with the potential for future advancements. As the proficiency and knowledge of the personnel increased, the accuracy of supplying the correct amount of water to the right place at the right time improved, and more water was saved.

Sharing close ties with Vaalharts irrigation scheme, Taung irrigation scheme was also recommended to adopt a similar approach under the guidance and supervision of the team. The use of modern tools and Information Technology could improvise water management practices in terms of computations as well as infrastructure maintenance ensuring easy experience sharing and a seamless knowledge transfer.

The Water Administration System (WAS) is designed to be a water management tool for irrigation schemes, Water User Associations (WUA’s), Catchment Management Agencies (CMA’s), and water management offices that want to manage their water usage, water distribution, and water accounts. 

The main aim during the development of the WAS program was to minimise water losses for irrigation schemes that work on the demand system and that distribute water through canal networks. Currently the WAS program is in use at all the major irrigation schemes cross South Africa and it manages an irrigated area of more than 142 000 ha including 9 500 farms. The main benefits of using the WAS program is: 

• The minimising of water distribution losses.
• The excellent management of water quota allocations and water usage per farmer.
• The availability of an extensive list of water reports on farm and scheme level.
• The increased productivity of scheme management personnel.
• An integrated debit accounting system that improves debit management.
• The improvement of the overall water administration management on irrigation schemes.

TYPES OF APPLICATION

WAS is an integrated database driven system with many water management capabilities. WAS can be implemented in a small water office that manages a few abstractions and measuring stations up to a CMA level that manages thousands of abstractions and measuring stations. WAS is used for the efficient administration of:

• Address information.
• Scheduled or rateable areas.
• Water quota allocations.
• Water delivered through pressure-regulated sluice gates, measuring structures and water
• Water transfers between users (Automatic and manually).
• Water use calculations for planted areas based on crop water use data.
• Date and time related flow data collected from electronic loggers or mechanical chart recorders.
• Discharge tables (DT) to do conversions between water depth and flow rate for measuring structures or vice versa.
• List of rateable areas (LRA) information.
• Calculation of water releases for water distribution through canal networks, pipelines and rivers taking lag times, evaporation, transpiration and seepage into account.
• Billing system that links to the water usage information.
• Flexible user charges based on water usage, a flat rate or scheduled area.
• Images and photos that can be linked to different types of information in the database.
• Automatic weather station database with a build in calculation of Eto values.
• Mail merge facility for sending letters to clients.

The WAS program saves all information in a Firebird database that can be installed on a single PC or on a server for use over a network. This makes it possible for the scheme manager, accounts personnel and water office personnel to access the database from PC's in their own offices. There is no limitation on the number of PC's that can be linked to the database.

What makes the WAS program unique is the fact that it is an integrated system that includes the water allocations, water use, water distribution and billing information. WAS will generate monthly invoices automatically using water usage or scheduled areas information captured in the database. Different user names and passwords can be used to control access to certain information in the database.