ASSESSMENT OF WATERLOGGING IN A CANAL COMMAND AREA USING REMOTE SENSING AND GIS

Abstract

India as an agrarian country and has been spending huge investments in agriculture and irrigation sectors since independence for construction, maintenance of major, medium and minor irrigation schemes. Self sufficiency came into reality during the period of Third, Fourth and Fifth 5year plans (1967 tol978) of the Green Revolution. Artificial irrigation, double cropping methods, high yielding varieties and intensive use of fertilizers has made green revolution a big success and India has transformed from food deficient country to an exporter of food grains. On the other hand, severe side effects have come up with irrigation projects related to drainage. While implementing irrigation projects drainage was not considered to an integral part of the irrigation schemes. This basic mistake has led to the conversion of large tracts of fertile land in to unproductive land with an alarming rise in water table. Waterlogging, salinity and alkalinity hazards are common features of the alluvial ayacut area. The problem of waterlogging and salinity have come up with the introduction of irrigation where we are trying to grow crops in arid and semi arid regions where naturenever intended water to flow as it does in our man made systems. The term waterlogging usually refers to a condition of high subsurface water table affecting the growth and yield of crops. On the other hand, accumulation of surface runoff and thereby stagnation of water over depressed lands due to the restriction of natural passages of water which may arise because of inadequate surface drainage or due to the higher water level elevation at the outfalls also cause waterlogging which is termed as surface waterlogging. Waterlogging and drainage problems of such nature pose a serious threat to the world's productive agricultural land. In India, about 10 million hectares of fertile land suffer from waterlogging, but apart from limited studies no systematic analysis of the consequences of waterlogging has been carried out. Waterlogging is an interactive problem but, in spite of its severity, policy makers have not paid attention to this since most decision makers have a fragmented view of irrigation systems, neglecting the linkages between agriculture, land use and irrigation. There are no systematic approaches or methods to assess the waterlogging as it is site specific and dynamic in nature. Criteria for extent of waterlogging differ with region. To reclaim waterlogged and saline land, frequent and systematic monitoring of the irrigated command is required as water is a depleting natural resource and soil is limited resource and has to be used efficiently. Advanced techniques like geospatial technologies are available presently to assess and manage precious natural resources. One has to use these techniques wisely to obtain the desired solution. So far, very few studies have been done on waterlogging and salinity by integrating the geospatial technologies with conventional modeling techniques. Soil and water resources are two indispensable components of agriculture. Their conservation and management is fundamental to the enhancement of productivity in agriculture. India has adopted several remedial measures and spends huge money to reclaim waterlogged and saline land yet the problem is there and farmers get affected. Recent studies show that agricultural production is also decreasing. In India, about 10 million hectares of fertile land suffer from waterlogging, unfortunately very little studies have been carried out where a systematic analysis to identify the consequences of waterlogging.India has only 2.4% of the world's total land area having 16% of the world's population; yet it has only 4% of the total available fresh water. Due to increasing growth in population, the availability of water on per capita basis, is steadily going down. Many areas of the country are already facing water stress. On one hand there is acute shortage of water in developing countries; while on the other hand, there are problems of waterlogging, improper utilization of water and degradation of land. One of the reasons for neglecting this problem is the difference in perception between the farmer and the high-level decision maker. A farmer would like to maximize the productivity of land with little emphasis on water use efficiency, whereas government agencies tend to plan cropping patterns based on maximizing the productivity of water. This divergence has been the basic reason for waterlogging in irrigation systems. Water being wasted has a high opportunity cost as it could be used in other areas having no irrigation facilities. Waterlogging reduces the potential of producing food in irrigated areas and it also reduces the possibility of extending irrigation to newer areas. Monitoring of irrigation projects periodically is equally important with initialization of new projects for sustainability of the system. In this context Tawa Command Area (TCA) under Tawa project situated in Hoshangabad district, Madhya Pradesh, India has been taken as a study area for the present study. Tawa iii project is a major canal irrigation system in Hoshngabad district. About 60% of the total area of Hoshangabad district is irrigated by Tawa canal system. The project is designed to provide annual flow irrigation of 0.333M.Ha in service area of 0.247 M.Ha of Hoshangabad District through Left Bank Canal (LBC) and right bank canal (RBC) System. In Tawa command there are two main crop seasons, Rabi (non monsoon) and Kharif (monsoon). In Rabi, wheat and gram are the main crops and in Kharif season Soyabean is the main crop. It is reported that there was a general decline in the water level in the area till 1975. In the Tawa command, the trend reversed to a rising ground water level since 1976, the time since regular canal irrigation commenced in the area. This rise in ground water level over the years is of the order of 2 m in general and more than 2.5 m in certain patches. It is reported that approximately 34000 ha of this command area is classified as waterlogged in the Tawa command after commencement of irrigation where water table lying between 0-3 m, out of which 330 hectares has completely gone out of production according to official estimates. Unofficial estimates put this figure around the order of 3000 ha. The difference in estimates of area affected by waterlogging occurs is due to the lack systematic methodology to identify and assess waterlogging on command area basis. In the present study a systematic methodology has been proposed to assess waterlogging using remote sensing and GIS coupled with Ground Water Flow Modeling (GWFM). Remote sensing data analysis has been done to prepare land use/ land cover map, crop discrimination and to identify waterlogging. Basic GIS thematic maps have been prepared which is prerequisite for any assessment and management related problems in a GIS environment. Manual methods of assessing waterlogging are difficult and time consuming on command area level. Making use of remote sensing methods coupled with field methods can be a best possible solution to identify waterlogging. Further it is difficult to use remote sensing methods to identify subsurface waterlogging, even it is done with indirect methods, and validation is required. In general number of observation wells to monitor water level are sparse and it is not feasible to use directly to know the water table condition on entire command area. Other parameters also have to be taken into consideration like geology, soil type, and land use to know the water table condition. To incorporate all these parameters, it is proposed to use ground water flow modeling by using inputs from IV remote sensing and GIS to overcome the difficulties in remote sensing and data constraints to assess waterlogging in the command area. In the present study Satellite imagery has been used to prepare land use/land cover map, to identify major crops and minor crops, and to identify waterlogging. To identify waterlogging with remote sensing techniques various Normalized Difference Water Indices (NDWI) proposed by various authors have been used and compared with each other in the remote sensing analysis. It has been observed that NDWI using Green and SWIR bands is the best method to identify waterlogged areas. Further to check the extent of waterlogging obtained from the remote sensing data analysis and to know the causative factors for waterlogging, GWFM has been developed. To know the interrelationship between causative factors GIS overlay analysis has been performed. Overlay analysis has been performed using inputs from remote sensing and GWFM to know the causative factors for waterlogging. It has been observed that extent of waterlogging is low as compared to area of the command however it may affect the individual farmer's socio economic status. Therefore micro level planning is required to combat waterlogging.