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Physical Papers.Pmd APPLICATION OF “SALTMOD” TO EVALUATE PREVENTIVE Nasir M. Khan*, MEASURES AGAINST HYDRO-SALINIZATION IN Bashir Ahmad**, M. Latif*** and Yohei Sato* AGRICULTURAL RURAL AREAS (A Case Study of Faisalabad, Pakistan) ABSTRACT the country, covering an area of 74,494 ha., to combat the twin menace (WAPDA, 1991). Monitoring and In Pakistan, the salt-affected soils are now covering evaluation of a project in different ways is a key-factor an area of 4.22 Mha, which constitutes about 26% of in its further planning and development. The irrigated rural area. About 55 Salinity Control and identification of causative factors and extent of the Reclamation Projects (SCRAP) were launched as a critical areas by salt-water balance studies help a remedial measures in the past with huge investments, great deal in the implementation of proper solutions mainly comprising vertical and surface drainage in future. system. The results were found generally far below expectations, due to many reasons/factors which were DESCRIPTION OF STUDY-AREA not taken into account before project-implementation. This model-study has been initiated, therefore, as an Large areas has been severely affected with the twin effort to test the generalized hydro-salinity model menace of waterlogging and salinization and ‘SaltMod’ for different soil and water-management thousands of hectares of land has gone out of scenaries and to evaluate the SCRAP project as production in the Fourth Drainage Project (FDP) area remedial measures in the rural areas in order to near Faisalabad. The FDP (SCARP scheme) project enhance over all agro-productivity. was initiated in 1983 and consists of many sub- drainage Sump units. The selected study area SIB-9 INTRODUCTION (Sump-9 unit), which was completed in 1989-90, is a part of this project, covering 121 ha and lying on the Secure balance in the global supply and demand for tail end of canal-irrigation system in the area (Figure- food has forced humans to develop agriculture in semi- 1). Physiographically, the area has almost flat arid to arid lands, which are generally less suitable topography (0.02%) with low annual rainfall (> 300mm), for agriculture and sensitive to environmental changes. and mean monthly maximum temperature is between Irrigation has always been considered as an effective 19.4 & 41.2 C . Geologically, the soils are alluvial way for progressive and sustainable irrigated deposits classified as silt loam, loam, and silt clay agriculture in rural areas since ancient times, to bridge loam and loamy sands. There are two cropping the gap of water-shortage. Large investments have seasons i.e. winter (Rabi) and summer (Kharif). Main been made in the past on irrigation developments, to Rabi crops (October-March) are wheat, sugarcane, maximize the production. Owing to irrigation-system, pulses, and fodder, while corn, paddy, cotton, the farmers have obtained quite stable productivity, sugarcane, and fodder occupy lands in Kharif season but they started facing an acute problem of (April-Sept.). waterlogging and salinity due to seepage from this huge system in most of the developing countries like DESCRIPTION OF THE HYDRO-SALINITY Pakistan. Sustainable agriculture is a most important MODEL AND DATA USED issue, not only for the rural community’s economic survival but also for the country’s economy to keep The hydro-salinity model ‘SALTMOD’ developed by balance with increasing demand of food. The farmers, Oosterbaan and Pedrose de Lima (1989) was selected and many local and international organizations are (for this study area) which computes the salt and water struggling now against the so-called ‘white death’ to balance for the root zone, transition zone and aquifer their lands. zone. The schematic illustration of SALTMOD is shown in Figure-2. The computation method A newly introduced tile-drainage system was installed SALTMOD is based on seasonal water and salt- as an alternative solution in appropriate locations of * Graduates School of Agriculture and Life Sciences, The University of Tokyo, Japan ** NARC, WRRI, Park Road, Islamabad, Pakistan *** Director (CEWRE), U.E.T., Lahore, Pakistan Quarterly SCIENCE VISION Vol.9 No.1-2 (Jul - Dec, 2003) & 3-4 (Jan - Jun, 2004) 111 Application of “Saltmod” to Evaluate Preventive Measures against Hydro-Salinization in Agricultural Rural Areas Figure - 1: Irrigation & Drainage Network at SIB-9 Area balance of agricultural lands, which can be expressed The data required by the model are seasonal average by the general water-balance equation as: values of the areal fractions of the rice and non-rice (all other crops), rainfall, depth of different soil-layers, Incoming Water = Outgoing Water ± (where leaching-efficiency values, initial salinity of the different is the change in water stored) soil-layers, groundwater and irrigation water, evapotranspiration, surface runoff, and reuse of The detailed method consists of a number of iterative drainage-water, etc. Model takes input-data of each calculations of water and salt-balance equations to year as average over two seasons, a wet and a dry find out the final equilibrium in each zone separately. season. Most of the data was collected on seasonal The method calculates the salt-balance for each zone, basis from Punjab Iirigation Dept., Int. Waterlogging based on the water-balance of the individual zone and & Salinity Research Inst., and Soil-Monitoring using their respective salt-concentrations of the Organization of WAPDA, Pakistan (WAPDA Annual incoming and outgoing water. The detailed principles Reports, 1990 - 1992) for the period of 1989-90 to of SALTMOD are reported in the manual published by 1991-92. These agencies are monitoring and analyzing ILRI, The Netherlands (Oosterbaan, 1989). different kinds of hydro-salinity (soils and groundwater) Figure - 2: Simplified Illustration of Waterbalance factors for SALTMOD 112 Quarterly SCIENCE VISION Vol.9 No.1-2 (Jul - Dec, 2003) & 3-4 (Jan - Jun, 2004) Nasir M. Khan, Bashir Ahmad, M. Latif and Yohei Sato Figure - 3: Simulated and Observed Water-Table Changes and climatic data for the study area and publish it on Once the model is calibrated and verified to the annual basis. acceptable limits, it can be then used to determine the future status of hydro-salinity for the area. Then, CALIBRATION AND VALIDATION OF THE MODEL after its validation to the area, the SALTMOD has been applied to predict the hydro-salinity status for the area After collection of necessary input-data, it was then for next 20 seasons, to evaluate the newly launched converted into the input-format as required by the SCARP (FDP project) in the area. All the results are model. The input-data for each year was given as discussed in detail below. average values over two seasons i.e. wet season (Kharif) and a dry season (Rabi) of each year, given RESULTS AND DISCUSSION separately to simulate the results for the next year. The model was applied to calibrate for local conditions Comparison of Watertable Fluctuations of SIB-9 area, under existing irrigation and cropping practices, to simulate seasonal watertable changes, SALTMOD was first calibrated for the seasonal root-zone salinity, quantity, and quality of tile drainage- change of watertable depth. The comparative results flow. The match of the data was obtained by optimizing show the higher watertable at initial stage than all the and varying the leaching-efficiencies and the natural later stages for the simulated periods and did not drainage to the aquifer, establishing the validity of the reach higher levels, as before, even after monsoon model. The simulated results were analyzed and rainfall (Figure-3). The decreasing trend of water-table compared with field-data collected for all four might be because of functioning of the drainage calibration-parameters and got statistically justified system, less rainfall and also due to the canal-closure by the model, which was modified to analyze the during Rabi season for one month, every year. measured and simulated results by statistical means. Generally the corresponding simulated seasonal The Model was also upgraded for checking some average trends are found in close agreement with the irrelevancy in the input-data, if given by user and give observed values (R2 = 0.72), if one observe as seasonal warning to make correction for that particular illogical single average, except for an exception during the input-combination of data. The model was also Kharif-1991 season, as the observed water-table modified for providing compatible tabulated results, remains higher in Rabi 90 than the simulated trend. easily accessible to any spreadsheet graphical This is because of the instantaneous heavy rainfall package like Lotus, Excel, for its quick graphical (136 mm) just before the Kharif season and the model comparative view. does not consider the instantaneous hydro-dynamics, but simulates the seasonal average values; the model has been developed for long-term predictions, which Quarterly SCIENCE VISION Vol.9 No.1-2 (Jul - Dec, 2003) & 3-4 (Jan - Jun, 2004) 113 Application of “Saltmod” to Evaluate Preventive Measures against Hydro-Salinization in Agricultural Rural Areas 3.9 225 Observed 3.7 200 Observed Simulated 3.5 175 Simulated 3.3 150 3.1 125 2.9 100 2.7 Drain Discharge (mm) 75 Root Zone Salinity (dS/m) 2.5 50 12345 123456 Seasons Seasons Figure - 4: Rootzone Salinity Comparison Figure - 5: Comparison of Seasonal Effluent Discharge depends more on long-term average input lower in Kharif season, with relaible matching (R2 =0.81) conditions of the area, rather than short-term with filed values (Figure- 5). Great variation was again variations, for macro-scale planning and evaluation found in Rabi season of 1990 in tile-flow due to the of reclamation projects. periodic rainfall as mentioned earlier. The other smaller variations seen are due to the collector-pipe laid at Change in Root-Zone Salinity greater depth, which remains in operation for a longer time, than the average drain-depth provided to the The SALTMOD simulated the soil-profile salinity and model as input.
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