ReseaRch PaPeR Journal of Agricultural and Marine Sciences Vol. 22 (1): 58– 62 DOI: 10.24200/jams.vol22iss1pp58-62 Received 15 Aug. 2016 Accepted 19 Feb 2017 Development of a decision support system for precision management of conjunctive use of treated wastewater for irrigation in Oman Hemanatha P. W. Jayasuriya*1, Ahmed Al-Busaidi 1 and Mushtaque Ahmed 1 * 1 Hemanatha P.W. Jayasuriya ( ) , Sultan Qaboos University, College of Agricultural and Marine Sciences, Dpt. of Soils, Water and Agricultural Engineering, Box 34, Al-Khod 123, Sultanate of Oman. Email: hemjay@squ.edu.om . Introduction As in any country or region with arid environ-ment, water is scarce in Oman. Yet the agri-culture is a common and traditional practice in Oman in which more than 50 percent of the arable lands are located in the northern coastal belt of Al-Bati- nah region (Alahakoon et al., 2013; MAF, 2013; MAF, 2015). The country with average annual rainfall around 100 mm, has limited natural freshwater resources and has been facing the serious problem of seawater intru- sion into the scarce GW reserves due to undisciplined excessive pumping of GW for irrigation from aquifers. Farmers are allowed to use GW with a quota system de- veloped by the two ministries: the Ministry of Agricul- ture and Fisheries and the Ministry of Water Resources (MAF, 2013; Mott MacDonald and MRMWR, 2013a; Mott MacDonald and MRMWR, 2013b; MAF, 2014; MAF, 2015). However, GW over pumping has been undisciplined and is a common practice among some farmers causing seawater intrusion and salinity issues in the region with most arable lands (Norman et al., 1998; Prathapar et al., 2005; Zekri, 2008; Alahakoon et al., 2013). There are problems with the crop selections and rotations as the farmers make own decisions on that issue without considering the water saving efforts. Some of the crops that have higher crop to water demand are grown by using inefficient irrigation methods (FAO, 1998; FAO, 2010; Somarathna and Ahmed 1999; Ensink et al., 2004). The researchers, with the support of the relevant ministries, have been looking for alternative options to minimize the use of irrigation water by over pump- ing of GW (Zekri, 2008; Alahakoon et al., 2013; Mott MacDonald and MRMWR, 2013a; Mott MacDonald and MRMWR, 2013b) and more efficient irrigation techniques (Zekri, 2008; Alahakoon et al., 2013; تطوير نظام دعم القرار إلدارة دقيقة الستخدام مياه الصرف الصحي املعاجلة واملخلوطة بعمان مهاناثا جاياسوريا*1و امحد البوسعيدي1و مشتاق امحد1 Abstract. This research aimed at finding alternative options for conjunctive use of treated wastewater (TW) with groundwater (GW) minimizing the irrigation water from aquifers in the Al-Batinah region with the assistance of a Decision Support System (DSS). Oman is facing a three-facet problem of lowering of GW table, wastewater over-pro- duction and excess TW. Approved guidelines for use of TW with tertiary treatments are of two classes: class-A (for vegetables consumed raw), class-B (after cooking). The developed DSS is comprised of four management subsystems: (1) data management in Excel, (2) model and knowledge management by macro programming in Excel, (3) with linear programming (LP) optimization models including transportation algorithms, and (4) user interface with Excel or Visual Basic (VB). The results are based on two extreme scenarios: zero TW excess, and zero GW used for irrigation. The DSS could predict water balance for number of crop rotations, and based on adjustable cost variables farmer profit margins could be created. Crop selections and rotation could be done using LP optimizations while transportation algorithm could organize best locations and capacities for treatment plants and the wastewater collection and transportation to farming areas via treatment plants. The developed DSS will be very useful as a water management, optimization and planning tool. Keywords: Decision support; precision irrigation management; conjunctive use; treated wastewater; groundwater. امللخــص: يهــدف البحــث لتحســن إدارة امليــاه اجلوفيــة وميــاه الصــرف الصحــي املعاجلــة عــن طريــق اســتخدام نظــام دعــم القــرار. تواجــة عمــان ثــاث حقائــق مائيــة وهــي اخنفــاض مســتوى امليــاه اجلوفيــة واإلنتــاج الزائــد مليــاه الصــرف الصحــي املعاجلــة مــع تزايــد كمياهتــا مــع مــرور الزمــن. يتكــون نظــام دعــم القــرار مــن إدارة األعــداد، اإلدارة املعرفيــة للربامــج، اإلدارة اخلطيــة للربامــج املســخدمة واســتخدام التداخــل العــددي يف الربامــج. اعتمــدت النتائــج علــى تصوريــن ومهــا االســتخدام الكلــي للميــاه املعاجلــة وعــدم اســتخدام امليــاه اجلوفيــة يف الزراعــة. تنبــأ النظــام بكميــات امليــاه املطلوبــة لعــدة حماصيــل منتجــة أثنــاء الســنة والــذي يدعــم ربــح املــزارع. مــن خــال النظــام قــد يكــون هنــاك تنبــوأت بنوعيــة احملاصيــل وتدويرهــا ممــا يتناســب مــع كميــة امليــاه املنتجــة واملنقولــة. النظــام اجلديــد ســيكون مفيــدا إلدارة امليــاه وعمــل املخططــات املســتقبلية. الكلمات املفتاحية: دعم اختاذ القرار، إدارة الري الدقيق، االستخدام املشرتك، مياه الصرف الصحي املعاجلة واملياه اجلوفية 59Research Article Jayasuriya, Al-Busaidi and Ahmed Alessandra, 2014) including precision irrigation (Zekri, 2008; Alahakoon et al., 2013). A consistent deficit of GW has been experienced due to irrigation use, and annual deficit of GW in the agricultural region Al-Batinah along was 315×106 m3 in 2013 (Zekri, 2008; Alahakoon et al., 2013; Mott MacDonald and MRMWR, 2013a; Mott MacDonald and MRMWR, 2013b). Due to people mi- gration to cities, city expansions and industrial growth have created excess production of wastewater. As per the statistics, there is a steep growth rate of wastewater production. Current daily wastewater produced in Mus- cat governorate is 94 000 m3 and predicted to be four fold in 2025 (Somaratna and Ahmed, 1999; Prathapar et al., 2005; Mott MacDonald and MRMWR, 2013a; Mott MacDonald and MRMWR, 2013b). Wastewater treat- ment plants have been established around the city with tertiary treatment levels, standard processes and quality; however there is not much effort made to use the water for consumable crop irrigation. Even after applying for various needs, there is a significant excess production of TW and handling this has become a challenge as there are restrictions for recharge (David and Williams, 1979; Berry et al., 1980; Harvey, 1997; Mohammad and Maza- hareh, 2003; Fluet et al., 2009; Bedbabis et al., 2010; Ab- delrahman et al., 2011; Al Khamis et al., 2011). Rationale The objective of this research was to find solutions for Oman’s three-facet problems of lowering of GW table (Al-Batinah GW deficit 315×106 m3 in 2013), increasing daily wastewater production (94 000 m3/day in 2015) and how to handle excess TW after reuse (Prathapar et al., 2005; Zekri, 2008; Mott MacDonald and MRM- WR, 2013a; Mott MacDonald and MRMWR, 2013b). The developed DSS can find potential solutions to all above-mentioned problems. A couple of key variables are kept in the system in order to maintain flexibility and adjustments. Following critical points and constraints were taken into consideration when developing the DSS for the use of TW for irrigation. Points considered on development: • It is important to find alternative options for replac- ing the irrigation water used by over pumping GW with the assistance of technology and planning. • The seawater intrusion, soil salinity, land degrada- tion hinder agricultural production. • Use of TW for irrigation is one of the best options, and the cheapest option in Oman to save GW. Constraints on implementation: • Acceptance by society to use in agriculture and agro industry; farmers, consumers, managers and the scientists. Many sensitive issues, need to be ad- dressed. • No storage facilities at sewage treatment plants (STPs) to store bulk of TW exit from the plant, transportation network should be efficient with Just-In-Time basis or dump in somewhere (in the ocean). Objectives The main objective of the study was to find alternative options for replacing the irrigation water used by over pumping GW (Zekri, 2008; Alahakoon et al., 2013, Mott MacDonald and MRMWR, 2013a; Mott MacDonald and MRMWR, 2013b) with the assistance of a DSS. The specific objectives of the study were to see the feasibility of maximizing the use of TW replacing GW use for irri- gation and to minimize the unused TW excess, optimize the land use for different crop combinations and rota- tions with TW use while optimizing the farmers’ profit, optimize the TW distribution network; determine the feasibility for locating STPs minimizing transportation (TW) cost for farmers, and develop a DSS for manag- ers to conduct feasibility studies for better planning and management of TW use. Methodology An Excel and Visual Basic based Decision Support Sys- tem (DSS) was developed to select options for conjunc- tive use of treated waste water (WT) and ground water (GW) for irrigation in Oman. The developed system targeted managers and farmers as users and the sys- tem was with necessary simplicity and flexibility. The system architecture utilized is illustrated in (Fig. 1). It comprised of four management subsystems; data man- agement in Excel, model and knowledge management by macro programming in Excel, with linear programming (LP) optimization models including transportation algo- rithms all in Excel, and user interface optional with Excel or VB mode. Graphical results could also be retrieved in the VB mode Two critical threshold levels were considered in the Figure 1. Architecture used in developing the Decision Support System. 60 SQU Journal of Agricultural and Marine Sciences, 2015, Volume 19, Issue 1 Development of a decision support system for the management of treated wastewater irrigation analysis considering the two scenarios shown in (Fig. 2). Threshold levels were: (1) Zero excess TW and (2) Zero use of GW based on the prevailing conditions in Oman. The main decision variable of the systems is the vol- ume of daily production of TW in 106 m3. In addition, there are other variables in the system applicable for different management modules (Fig. 1). As an example, for the cost analysis, prices of TW and GW (including transportation costs) are auxiliary variables. Once all the variables are entered, the results including graphical re- sults will appear (Fig. 3). Crop and meteorological data are based on the experimental farming by the MOAF Oman. Results Figure 3 shows a sample view of Excel-based decision support system and results with graphics obtained un- der given data and applied decision variables. Table in (Fig. 3) shows the three crop rotations and two extreme scenarios of zero excess TW and zero GW use. Extended portion of the table shows the cost of excess TW or the opportunity cost. The bottom left section shows the cells for decisions variables used in the computations: daily TW production costs for TW and GW ,etc. The bottom area shows the cost analysis results in graphical form. Decision makers can observe the simulation results and select the appropriate crops and cropping enterprises leading to profit maximization while maintaining the optimum conjunctive use of TW and GW. Figure 2. The two extreme scenario considered : (1) zero GW use, i.e. the peak of treated water production is con- sidered as the peak of irrigation water requirements and (2) zero TW excess, the minimal requirements for the dif- ferent crops is provided by treated water and additional GW is used when necessary. Figure 3. A sample view of Excel-based DSS on farmer profit maximization condition. 61Research Article Jayasuriya, Al-Busaidi and Ahmed Figure 4 shows a sample view of the VB interface window which provides the results in tabular form with cells having decision variables for adjustments. The up- per row of the table shows option buttons (Summery, Rotations, Profits, LP, LP-Transportation etc.), through which corresponding programs could be executed in Excel and results could be obtained in the VB window. The cells in the upper rows provide the main decision variables for necessary adjustments and tables show the corresponding results. The graphical results (bar charts) obtained in Excel could also be retrieved in the VB mode. The system provided greater simplicity and flexibility, and with a short training the users will be able to operate the system. Conclusion and recommendations • The developed DSS could simulate best options with conjunctive use of TW and GW for scheduling seasonal irrigation in Oman. • The developed DSS could simulate potential solu- tions for the Oman’s three-facet problems; reduce the use of GW lowering the stress on GW table, maximize the use of TW without dumping in sea, and system could be used to plan the locations for treatment plants and two-way transportation net- work with quantities. • The developed DSS is very simple, flexible and us- er-friendly. It can be further improved with exten- sions incorporating leaching fraction, soil/water salinity fractions etc. Acknowledgements The authors wish to acknowledge the financial sup- port given by the USAID-FABRI program through the MENA research network and the facilities provided by the Sultan Qaboos University (SQU), HAYA Water LLC and Dr. Saif Al Khamisi of Ministry of Agriculture and Fisheries, Oman for the valuable contributions by pro- viding field data. References Abdelrahman, H. A., Alkhamisi, S., Ahmed, M., and Ali, H. 2011. Effects of treated wastewater irrigation on element concentrations in soil and maize plants. Communications in Soil Science and Plant Analysis. 42: 2046-2063. Alahakoon, M., Jayasuriya H.P.W., Slim Zekri, Riadh Zaier, Al-Busaidi, H. 2013. Design of a database and wireless data retrieval systems for monitoring irriga- tion in Al-Batinah Region in Oman. 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