Assesment of area and water allocation in canal command of purna irrigation project using swat
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Date
2018
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Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani
Abstract
Agriculture is the primary consumer of water a complex natural resource but its availability is highly uneven in space and time. Since the demand of water in the non-agricultural sectors is increasing day by day, its share for agriculture is expected to reduce. Management of surface water available in river basins is the major challenge due to its low water use efficiency and equitable distribution. Consequently, major research challenges are therefore to grow more food from less water that maximizes water-use efficiency and available water supply to all farmers in command area. The modern GIS techniques coupled with hydrological models can quickly guide the management in decision making, since the temporal and spatial dimensions could be studied at once. Hence a study was undertaken to quantify the surface water resources within the catchment area of Purna reservoir a major irrigation project in Marathwada to assess the total water demands with major crops cultivated using Soil and Water Assessment Tool (SWAT) model. Study also was aimed to analyse the existing water allocation strategies and cropping pattern for suggesting optimum cropping pattern based on performance indicators and net benefit from the project.
The data on daily meteorological data (1979-2013), satellite digital images, soil characteristics, daily reservoir gauge levels, canal network details, daily canal water release, year-wise cropping pattern in the command area and area under cultivation of various crops of Purna Irrigation Project were collected. Two SRTM images (SRTM_52_08 and SRTM_52_09) with 90 m x 90 m resolution were downloaded from NASA website to prepare DEM of the study area using ERDAS Imagine software. The geospatial input data namely, Digital elevation model (DEM), land use land cover (LULC) map and Soil textural map required to run SWAT were prepared in ArcGIS environment. Database on climate, soil, crop, drainage network, ground water, reservoir and management practices were prepared in MS ACCESS.
The SWAT model was used to assess the water availability in Purna reservoir using DEM, weather data and hydrological details of catchment as well as canal command. The catchment area of Purna reservoir was divided in to 4 subbasins and 14 HRUs (hydrological response unit) were created by over laying LULC map, soil map and slope map with appropriate threshold values given manually. The total simulation period was from 1992 to 2013 of which about two-third of the data was of total simulation period (1992-2013) was used for calibration (1992-2004) and the remaining (2005-2013) for validation. The stream flow and the reservoir storage volume data measured at the outlet of the reservoir were used for calibration and validation of SWAT using SWAT-CUP software with SUFI-2 algorithm. The performance of model was assessed based on Pearson’s correlation coefficient (r), Coefficient of determination (R2), Index of agreement (d), Nash-Sutcliffe efficiency (NSE), Root mean square error (RMSE), RMSE-Observations standard deviation ratio (RSR), Percent bias (PBIAS), p-Factor, r-Factor and graphical techniques.
Water balance estimation was done based on the water availability in the reservoir and water demand from various water using sectors in the command area. Command area of PIP was delineated using predefined watersheds and streams. For the command area 67 Allocation Units within 12 sub-basins with a combination of soil, land utilization and slope categories. Stage wise crop coefficients (Kc) were developed for accurate estimation of water requirements of various crops using standard procedure. The rotation wise canal water released data were also collected and compared with the crop water requirements for major crops cultivated under canal command area of Purna irrigation project.
Performance evaluation of canal water delivery system was carried out using various performance indicators viz, adequacy, efficiency, equity, dependability, deficiency and wastage. Crop growth module of SWAT was used to get the simulated yields of crops grown in the command area. Economic analysis of project was done using cost of cultivation, average productivity of crops and minimum support price.
The data indicates that soils in the catchment and command of Purna reservoir have the basic infiltration rate of 14.3 mm hr-1 to 35.9 mm hr-1. The depth of soil ranges between 100 mm to 1070 mm with soil organic carbon ranges from 0.28% to 1.26%. The average available live storage in reservoir from last 45 year period was observed as 64.27 % of its maximum storage capacity.
The SWAT performed well in simulating reservoir storage and flow volumes throughout simulation period whereas SWAT over predicted the magnitude of monthly reservoir storage volume during high rainfall events. During the study period (1992 to 2013) average water available in the reservoir was 927.72 Mm3 out of which 540.92 Mm3 water was utilized for irrigation, drinking and water lifting 351.15 (37.85 %), 29.41 (3.17 %) and 19.07 (2.05%) Mm3, respectively with 386.12 Mm3 of water remained as storage at end of the season.
The land utilization pattern of the command area showed 57988.04 ha (64.06%) area under cultivation out of the total area (90525.57 ha) followed by the area under pasture (19471.53 ha, 21.51%). The area under waste land and grazing land can be developed and brought under horticultural crops.
The major portion of command area represents sandy clay loam soils (24.79%) and sandy clay soils (23.96%). Results indicated that there is large scale deviation from the approved cropping pattern. Although the soils are mostly non-saline, about 15 per cent of the profiles examined have been classified as alkaline having pH more than 8.6. The land irrigability class II is the major in command area of PIP covering 23536.65 ha (26%) area under it, followed by class VI occupying the area of 20820.88 ha (23%) and class III covering 18105.11 ha (20%) area. The land slope class 0.0-0.5 per cent covers the maximum area of 53256.19 ha (58.83%) followed by slope class 0.5-1.5 (15615.66 ha, 17.25%) and land slope class 1.5-2.5 (11007.91 ha, 12.16%).
Soybean with 15627 ha area under cultivation has emerged as the major kharif crop in command area (27%) followed by wheat (25.23%) in Rabi season and sugarcane (8.28%) as perennial crops. Among the various crops grown under canal command of Purna irrigation project the banana (2579.33mm) and sugarcane (2477.17 mm) have the highest seasonal reference crop evapotranspiration. The study revealed that the catchment is relatively sensitive to the increase water demand scenario and irrigation projection, suggesting that the slight changes will alter the present and future water availability. Results also indicate a general trend of declining water supply and increasing unmet demand in the catchment area of Purna reservoir and its canal command area.
During the study period the maximum area under irrigation was in 2013-14 (50,083 ha) and minimum area under irrigation was found in the year of 2004-05 (7,366 ha). Study suggests that there is a need to improve the canal delivery performance with some modifications in the operation and management of canal system, since the overall performance of canal system is poor because of most of the canal water distribution network is unlined except main canal. Due to unlined canal water distribution network most of the water is losses during conveyance of water from main canal network to field channels.
Arc-SWAT interface has proven its applicability on a large scale under temporally and spatially distributed conditions. The crop economics and project net benefit from existing cropping pattern based on the total production (Y), consumptive water use (ET) and crop water productivity (CWP) indicated that the total area under cultivation, total production and total return gained were 30731.57 ha, 625518.66 Mt and 210.67 crores, respectively. The B: C ratios were higher for wheat (1:2.68); Rabi sorghum (1:2.60) and gram (1:2.63) as compared to turmeric (1:2.23) and groundnut (1:1.31). The perennial crops sugarcane (1:1.39), banana (1:2.24) and sweet orange (1:1.51) have lowest B: C ratio. The study concluded that among the various scenarios developed, the best optimal cropping scenario will be with the 53% cropping intensity consuming 70% of available water in the reservoir. However there is a need to grow low water requiring crops with elimination of high water requiring and low profitable crops. The area curtailed from sugarcane and groundnut can be brought under turmeric, cotton and sunflower crops.
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