The implementation of the water release module of the WAS program at the Vaalharts Water Users' Association

Abstract

Food and water are two basic human needs. International projections indicate that water shortages will be prevalent among poorer countries where resources are limited and population growth is rapid, such as the Middle East, parts of Asia and Africa. Provisional estimates are that South Africa will run out of surplus usable water by 2025, or soon thereafter. Urban and peri-urban areas will therefore require new infrastructure and inter-basin transfers to provide safe water and adequate sanitation. Due to the high cost of these developments, such water is seen as being used for industrial and public needs only and not for irrigation. Currently, the agricultural water users consume the majority of the water used by humans. Taking cognisance of the before mentioned it is a reality that in the future the irrigation sector will have to sacrifice some of its water for public and industrial usage. This suggests growing conflict between the different water users and the agricultural water users. An attempt by the Department of Water Affairs and Forestry (DWAF) to address this conflict has been the implementation of pilot studies to determine the steps

Water User Associations (WUAs) could take to ensure more effective water use in the future by the agricultural sector. These steps include an increase in irrigation efficiency according to the benchmarks of crop irrigation requirements and more efficient dam and canal management. The Water Administration System (WAS) has been developed to fulfill this exact requirement as it ensures optimal delivery of irrigation water on demand. The program is designed as a management tool for irrigation schemes, WUAs and water management offices to manage their accounts, and also to manage water supply to clients more efficiently through canal networks, pipelines and rivers. The WAS program consists of four modules that are integrated into a single program. Three modules of the WAS program have already been implemented at the Vaalharts irrigation scheme. This scheme has been transformed from a government controlled scheme to a privately owned scheme, and is now known as the Vaalharts Water User’s Association (VHWUA). The main purpose of this study was to implement the fourth module of the WAS program at the VHWUA as only full functionality of the complete program will ensure effective water use at the scheme.

The fourth module calculates the volume of water to be released for all the canals (main canal and all its branches), allowing for lag times, water losses and accruals in order to minimise waste and thus save water. The methodology followed in this study was to first of all develop an understanding of the distribution cycle and the current calculation procedure of the VHWUA. The fourth module was then applied on a typical feeder canal and used to calculate the release volumes in order to compare these results with the current values. The next step was then to verify all data abstracted from the database used by the WAS program to calculate the release volumes. The database consists of information like cross-sectional properties, positioning of the sluices, canal slope, as well as canal capacities. The verification of data was done by field work, by studying existing engineering design drawings, through meetings and consultations with all parties involved in the VHWUA as well as by mathematical calculations. Cross-checking and verification, if necessary, of all above mentioned data were done. After the verification process, the database was updated and another cycle of calculations were run to do the final calibrations. Accurate calibrations were done to the seepage and the lag time coefficient. Some final adjustments were also made to the canal geometry in the database. This was an important part of the study as only a trusted and verified database will deliver correct results, irrespective of the software program used.

After calibration of the database, the fourth module was again applied, but this time water losses were included in the calculations and the results revealed trustworthy and accurate real-time release volumes. The study therefore succeeded in the implementation of the fourth module on a typical feeder canal at the VHWUA. The study was concluded by the compilation of a checklist, which the VHWUA can use to implement the module on the whole scheme. This would enable the VHWUA to implement and apply the complete WAS program, which offers all the benefits and answers in every need of any water management office. Sustainable water resource utilisation can only be achieved through proper management. Applying this most effective management program will ensure a cost effective and optimised process at the VHWUA.