Water Conservation using Alternate Irrigation Practices Hadiqa Maqsood1, S. Imran Ahmed1, Bashir Lakhani2 1
NED University of Engineering & Technology 2 Techno Consult - International
[email protected]
ABSTRACT With the growing population, the main concern to world is to fulfill the food and fiber requirement for present and future. This issue has subsequently created an imbalance between water supply and demand, since major section of water is devoted for irrigation, especially in Pakistan. In order to increase productivity (yield per area) using less or available water, various alternative irrigation practices are now being applied. This study is an effort based on the efficient water management techniques for Porali River Basin, Lasbella, Balochistan. The study crop is cotton as this is the most grown crop for this region. Presently, basin/border irrigation system is being implemented in this watershed which fallout with approximately 30% losses. A computer simulation model, NCRS _SURFACE, is used to simulate alternative irrigation systems in order to decrease the losses and conserve water, consequently. Results showed that using conventional system 3 x 106 m3 of water could be saved. Additionally, surge and alternate furrow systems showed exceptionally good results with satisfactory efficiencies (79 to 83%), minimal losses (15%) and water conservation up to 1.2 x 107 m3. Based on the conserved amount of water, increase in command area was calculated, showing 2.18 x 106 m2 for conventional and 9 x 106 m2 for surge and alternate furrow systems. Keywords: Furrow, Irrigation requirement, Surge irrigation, modeling INTRODUCTION Water management is the key element in irrigation systems in order to attain maximum yield with controlled amount of water. Irrigation is an artificial means to provide water to the arid zones to fulfill crop water requirement. Studies have been done to improve the irrigation systems throughout the world. There are various models available to simulate the real life scenario, such as AquaCrop (FAO 2011), a new version of CROPWAT, designed to simulate biomass and yield responses of field crops. There are drip (trickle) irrigation systems and sprinkler systems that are efficient up to 90% or more, but expensive to install. Acar et al. (2008) provided the importance of pressurized systems elucidating that these systems decrease evapotranspiration to 3 – 4% from normal range, and losses to less than 1%. They further mentioned the high installments costs for some crops and requirement of technical expertise. This is a drawback since developing countries could not afford to install such systems on large scale and there is lack of technical skills. To overcome this hurdle, other systems or techniques should be studied that are inexpensive and can necessitate the efficiency of the systems. Sarwar et al. (2002) carried out their study in Punjab province of Pakistan, indicating the effect of deficit irrigation on crop yield using Soil-WaterAtmosphere-Plant (SWAP) model. They studied various irrigation schedules to enhance the productivity and results showed that 25% of water could be saved with 30% increase in yield. Surge irrigation and alternate furrow irrigation are one of those alternatives that are inexpensive yet efficient. The surge flow concept in surface irrigation was first introduced at Utah State University by Stringham and Keller (1979). Surge flow irrigation creates a series of on and off cycles of water flow, whereas, alternate furrow is water application to every alternate furrow of the field. Mitchell and Stevenson (1993) compared surge and alternate furrow irrigation systems for Madras loam soil. Their results indicated that surge and alternate furrow are very beneficial in terms of saving water with no significant yield loss. For Porali watershed, modeling will be done for all three systems (furrow, alternate furrow and surge) to identify their efficiencies, amount of water and respective economic benefits.
Objectives The main objective of this study is water management for an arid zone. The specific objectives are; Modeling effect of irrigation strategies on cotton for water conservation, and Analysis of benefits of water limiting scenario. MATERIAL AND METHODS Study Area Porali River watershed lies in the southern part of the province of Balochistan having coordinates of 25°58‟0”N and 66°25‟60”E. This area has hot, dry tropical climate with the temperature during summer rising up to 42˚C. The average annual rainfall of this area is not more than 170 mm. Irrigation is being carried out in this region since centuries and various crops of both seasons, Rabi and Kharif, are grown here. Figure 1 is the map of Porali watershed highlighting the cultivation land.
Figure 1: Map of Porali watershed showing cultivated land use. Study Crop Various crops such as fruits, vegetables, wheat, fodder, cotton, banana, bajra, and castor seeds are grown in Porali watershed with its requirements based on climatic conditions. The crop taken for this study is cotton. This Kharif crop is the most cultivated crop in this watershed, covering area of about 1.6 × 107 m2. Its growing season is 5 months starting from August till December. For this season, the average evapotranspiration (ET) in Porali watershed is 3.75mm/day. The root zone depth is 1m and crop water requirement (CWR) is 1025mm. From the obtained data it is observed that 5 irrigations are required during the growing season of cotton. Data collection The data required for this study are as follows;
Table 1: Data and their sources Data Cultivation land layer (2013) Cultivation description (area, no. of irrigations, etc.)
Sources Techno Consultants Pvt. Ltd.
International Union for Conservation of Nature (IUCN), Water Program, Balochistan
Crop water requirement of cotton
Irrigation approach in Porali watershed Being in an arid region, most of the irrigation practices have been based on surface irrigation at Porali basin. Most common irrigation systems at Porali are basin and border with rudimentary arrangement. There are two basic approaches for which water management benefits are carried out; land limiting scenario and water limiting scenario. For Porali River Basin, land is not the issue; it is water, the quantity and its coherent utilization. Table 2 highlights the sub catchments where cotton is being cultivated. Table 2: Areas of regions for cotton cultivation in Porali watershed S.no Regions Area covered by Cotton(Ha) 1 Kharrai 97 2 Kud 688 3 Wadh 607 4 Taddar 119 5 Khanko 14.6 6 Gajri 24.2 7 Ping Jhal 9.7 8 Khaniki 49.4 9 Kulri Total Area (Ha) Total Area (m2)
54.5 1664 1.6 × 107
To calculate irrigation requirement and/or amount of water, it is essential to know the net irrigation depth (in) of the crop. Net irrigation depth is calculated using the following methodology; No. of days of growing season x ET = Total in Total in / No. of irrigations = in per irrigation Therefore, (5 months x 30 days a month) x 3.75 = 562.5 mm And, 562.5/5 = 112.5 mm Net irrigation depth does not cater any losses of the system that exist, conversely. Therefore, irrigation requirement is calculated and consequently, the average amount of water required for irrigation is attained. The formula for irrigation requirement is, IR = (ET –Pe) x (1 – LR) /E
(1)
Where, IR = Irrigation requirement (mm) ET = Evapotranspiration (mm/day) Pe = Effective precipitation (mm) LR = Leaching requirement E = Efficiency (%) Since the irrigation system in Pakistan is mostly 50% efficient. Therefore, with 50% efficiency, 30% losses and leaching requirement of 1.16, irrigation requirement is calculated for cotton. The total amount of water required is calculated using,
Amount of water (m3) = Irrigation requirement (mm) × Area (m2)
(2)
Furthermore, from the results of model, gross irrigation depth is also calculated to attain volume of water. Below is the mentioned equation. ig = 60 x Q x Tco / W x L
(3)
Where, ig = gross irrigation depth Q = Flow rate (L/s) Tco = Cut off time (min) W = Furrow spacing (m) L = Furrow length (m) All the above equations have been extracted from “Irrigation System Design” by R. Cuenca. Alternative irrigation practices In order to conserve water with adequate efficiency, following methods are suggested and analyzed. 1. Furrow Irrigation 2. Alternate furrow Irrigation 3. Surge Irrigation Since the cultivated area of cotton is vast, a design field of 136 m x 155m is modeled, having slope 0.005 with 0.56m furrow width. These three methods are compared with basin/border system to analyze the competence of each. Model Interpretation Modeling has become one of the most efficient means of simulation and scenario based analysis. Various irrigation models have proven to provide satisfactory results based on required outputs. The model used for this study is NRCS –SURFACE, a simplified version of SIRMOD III (Surface Irrigation Evaluation and Simulation Program). This model has been developed by Department of Biological and Irrigation Engineering, Utah State University, Logan, US. Its technical documentation was published in 2003, although the work on equations and constants has been carried out since 1997. Following are the inputs required for the model; 1. Inflow Controls 2. Field topography 3. Infiltration characteristics Following are the outputs of the model; 1. Efficiencies: (application efficiency, distribution efficiency) 2. Volume balance: (percentage of losses as deep percolation or outflow) NRCS –SURFACE illustrates fine infiltration rate graphs for every selected flow regime. The visuals show a continuous movement of water as runoff and percolation for one furrow. Modeling is performed for all three systems for cotton. For surge irrigation system, three number of surges are assigned to the model. RESULTS AND DISCUSSION For basin/border system the calculated irrigation requirement is shown in table 3. Table 3: Irrigation requirement and volume of water of cotton for basin irrigation system. Crop CWR (mm) Losses IR(mm) Area (Ha) Area (m2) Amount of water (m3) Cotton
1025
1.3
1332.5
1664.49
16644900
22179329.25 7
2.2 × 10
Using crop water requirement (CWR) and 30% losses, irrigation requirement was calculated for all the crops which concludes that amount of water being used for irrigation purpose is 2.2×107 m3. Table 4 shows the input data placed for all three irrigation systems in NCRS – SURFACE model. Table 4: Input data for the model. Cut off Irrigation system Flow rate (L/s) time(min) Conventional 1.01 221 Irrigation Alternate Furrow 0.45 439 Irrigation 7.19 142 Surge Irrigation For alternate furrow irrigation system, each furrow will receive half of the amount applied in furrow. Therefore, 0.45 L/s, approximately half of 1.05 L/s, is assigned to the model. Moreover, the cut off time will also increase since the water has to seep through the furrows to cater the neighboring furrow. Figure 2 shows the prototype model simulation for furrow and alternate furrow. A very fine infiltration curve can be seen, where some amount of water is exceeding root zone depth (zreq), resulting in deep percolation, the values of which are mentioned further. For surge irrigation, the water applied is 7.19 L/s which is more than furrow but since the cut off time is low i.e. 142 minutes, the amount of water is conserved, consequently. Cut off time is low because water is being provided in intervals. These values are selected as most suitable after various iterations. Figure 3a and 3b are illustrating application of first and second surge, respectively. The figure effortlessly shows the movement of water along the furrow. Table 5 illustrates the efficiencies of each irrigation system designed. Table 5: Efficiencies; output generated by the model Irrigation system Application efficiency Distribution efficiency (%) (%) 73.4 83.66 Conventional 83.3 85.8 Alternate furrow 79.4 56 Surge Irrigation Furthermore, model illustrated deep percolation and outflow losses, which as illustrated in table 6.
Irrigation system Conventional Alternate furrow Surge Irrigation
Table 6: Losses; Output generated by the model Deep Percolation Runoff depth (mm) Depth (mm) 18.06 0.75 2.53 0.61 9.04 0.01
Total Losses (mm) 18.81 3.14 9.05
On comparison of tables 5 and 6, it can be elucidated that conventional system is giving excellent efficiency, with some losses (19%). The losses in conventional system are typically deep percolation. This is because flow is continuous for the set time, making the initial quarters of field highly saturated which eventually exceeding root zone depth. The results for alternate furrow show exceptional application efficiency of 83.3%. A very notable decrease in losses is seen, highlighting the fact that irrigating via alternate furrow will save water from deep percolation and runoff. Alternate furrow is giving the minimum losses which are the pivotal purpose of this study. The third design, surge irrigation system, shows 79.4% of irrigation efficiency, which is the lowest, comparatively, still within satisfactory range. Moreover, the losses have decreased to 9.05mm.
To explicate the amount of water required for each suggested system, calculations are done for the whole growing season of cotton. Table 7 describes the results very comprehensively.
Irrigation system
Conventional Alternate Furrow Surge
Table 7: Derived volume of water for every design system. Gross Infiltration Gross Infiltration Gross Infiltration Depth/ Irrigation depth for growing depth for growing (mm) season (mm) season (m) (a) (a) x 5 (b) 131.3 656.5 0.6565 116.2 581 0.581 121.5 607.5 0.607
Amount of water (m3) (b) x Area (b) x (1.6 x 107) 1.9 x 107 9.6 x 106 1 x 107
7
On comparison with border, that depicted 30% losses and volume of 2.2 × 10 m3, the amount of water simulated for every system is less. Alternate furrow is utilizing the least amount of water, conserving 1.2 x 107 m3. Moreover, prominent volume of water is saved in furrow and surge practices. Table 8 shows the amount of water that can be conserved on applying these alternatives for cotton.
Irrigation system Conventional Alternate furrow Surge
Table 8: Water conserved by each design system. Existing volume being Derived volume (m3) 3 utilized (m ) 1.9 x 107 2.2 × 107 9.6 x 106 2.2 × 107 1 x 107 2.2 × 107
Water conserved (m3) 3 x 106 1.24 x 107 1.2 x 107
Similar amount of water is being conserved in alternate furrow and surge irrigation technique. Table 8 gives water conservation amount for cotton only. In Porali watershed, various other crops such as wheat, maize, banana, castor seed, etc. are cultivated. If such practices are applied for other crops, the water conservation would be very beneficial in terms of productivity and finance. Based on the volume of water conserved, increase in command area is depicted. Table 9 shows that from 3 x 106 m3 of conventional system, 2.18 x 106 m2 of area can further be utilized for irrigation. In addition, alternate furrow and surge irrigation system show almost 9 x 106 m2 of increase in command area. Table 9: Increase in command area for every irrigation practice. 7 Increase in command Area = 1.6 10 m2 2 7 3 area(m ) = Area × water Existing water = 2.2 × 10 m Irrigation System conserved Water conserved (m3) Existing water 3 x 106 2.18 x 106 Conventional 7 1.24 x 10 9 x 106 Alternate Furrow 7 1.2 x 10 8.7 x 106 Surge
CONCLUSIONS AND RECOMMENDATIONS The conclusions drawn from the study are: All three systems show good efficiencies, with alternate furrow showing the highest (83%) followed by surge, and conventional (79 and 73%), respectively. In addition, alternate furrow has depicted minimum losses (around 4%), followed by surge and conventional (9 and 19%), respectively. Simulation for conventional illustrates 3 x 106 m3 of conservation with possible increase of 2.18 x 106 m2 in command area. Alternate furrow and surge irrigation system show 1.2 x 107 m3 of water conservation that results in increase in command area of about 9 x 106 m2. The benefit of increase in command area is increase in crop yield and the economy, eventually.
It is recommended that these practices be followed for other crops in this watershed to benefit the agriculture and local community. References 1. Sarwar, A and Perry, C 2002, „Increasing Water Productivity through Deficit Irrigation: Evidence from the Indus Plains of Pakistan‟, Irrigation and Drainage, vol 51, pp. 87–92. 2. Acar, B, Topak, R., Direk, M. and Ugurlu, N 2008, „Importance of Pressurized Irrigation Systems in Arid Areas: A Case Study of Konya- Turkey‟, J. Int. Environmental Application & Science vol 3 no. 4, pp. 265-270. 3. FAO Water Development and Management Unit, AquaCrop version 3.1+ 2011. Available from: http://www.fao.org/nr/water/aquacrop. 4. Stringham, GE, and Keller, J 1979, „Surge flow for automatic irrigation‟, ASCE Irrigation and Drainage Division Specialty Conference, Albuquerque, NM pp. 132- 142. 5. Mitchell, AR, and Stevenson, K 1993, „Surge flow and alternating furrow irrigation of peppermint to conserve water‟, Central Oregon Agricultural Research Center Annual Report: pp. 79-87. 6. IUCN 2006, Water requirements of major crops for different agro-climatic zones of Balochistan, Water Program, Balochistan Program Office, pp. 139 -158. 7. Walker, WR 2003, SIRMOD III. Surface Irrigation Simulation, Evaluation and Design, Guide and Technical Documentation. Department of Biological and Irrigation Engineering, Utah State University, Logan, USA. 8. Cuenca, R 1989, Irrigation System Design. An Engineering Approach, Prentice-Hall, New Jersey, US.
Figure 2: Model simulation for furrow & alternate furrow.
Figure 3a: Model simulation for surge system; First surge
Figure 4b: Model simulation for surge system; Second surge
