PERFORMANCE EVALUATION OF SELECTED TANK IRRIGATION PROJECTS IN KSHIPRA BASIN

Abstract

An irrigation tank is a small reservoir constructed across the slope of a valley to catch and store runoff during monsoon season. The tank irrigation has a special significance to the marginal and small scale farmers as these systems are less capital intensive and have wider range of geographical distribution than large projects. Man-made reservoirs of small capacity (known as tank) are crucial for irrigation as well as for recharging groundwater in draught prone regions. This study was taken up for performance evaluation of two selected tanks, Silarkhedi and Jastakhedi in Kshipra basin in Madhya Pradesh, India. The study covers the following. • Field observations on O&M status of the projects, discussion with farmers and data collection • To study the water balance of tanks to assess spill in monsoon season and diversion of water for irrigation in non-monsoon over a period of twenty years (1999-2000). • To evaluate changes in crops, crop area and seasonal irrigation water demand under design, existing and proposed modernization conditions. • To evaluate changes in ground water availability and its utilization. • To suggest improvements in management of the projects. Some important observations from field investigation and discussion held with farmers are as given below. (i) Farmers in head reaches of canal over draw irrigation water, which leads to reduction in irrigated land as the farmers in tail reaches do not get water for irrigation, (ii) Introduction of hybrid variety of wheat has led to higher consumption of water and hence shortage of irrigation water and consequent reduction of irrigation land, (iii) Non-provision of micro distribution network has led to inefficient use of irrigation water, (iv) There is no regular interaction between Govt. officials and farmers. Therefore, farmers seldom have opportunity to communicate their problems, (v) The maintenance is substandard, (vi) Rabi crops (wheat and gram) were extensively cultivated on the bed and land on periphery of tank. Monthly water balance computations were made for monsoon (1st June to 31st Oct) to assess releases/spill and for non-monsoon season (1st November to 31st May) to assess irrigation diversion using hydro-meteorological data over the period of twenty years (1987-88 to 2006-. 2007). Linear decrease in storage was assumed during non-monsoon season due to regular withdrawal of water from tanks. Components like evaporation and seepage losses were found significant and were accounted in the water balance computations. From the simulation study (1987-2006), It was found that spills (d/s releases) occurred in both the tanks on an average of once in every 2 years. The average annual releases in downstream over the 20 years period were 3.104 MCM and 2.4125 MCM in Silarkhedi and Jastakhedi tanks respectively. Observed data of eight permanent observation wells of Ujjain Block, M.P. (1999-2006) have been analysed. Falling water level trend in pre-monsoon and post-monsoon are found to be 23.42cm/year and 15.06 cm/year respectively. Average water level fluctuation between pre and post monsoon is found to be 3.46m. Groundwater draft at present (for irrigation and domestic and industrial use) and allocation for all uses in future use have been estimated. Recharge from various sources such as canal seepage, surface water irrigation, groundwater irrigation and tanks have been computed. Rainfall Infiltration (RFI) Method and Water Table Fluctuation (WTF) Method have been used to estimate the monsoon rainfall recharge to the groundwater. Though water level trend shows falling trend in the region, groundwater in the tank commands may be considered for supplementary use of irrigation, due to recharge from various sources. Further, it may be utilized for domestic and industrial use if managed in an effective and efficient manner. Using windows version CROPWAT model of FAO, reference evapotranspiration has been estimated for the catchment and command areas of both the tanks. Two methods namely FAO/AGWL and USDA-SCS have been used to assess the effective rainfall of the study areas. Wheat and gram were supposed to be irrigated being dominant crops as per earlier design of the tanks. However in prevailing condition, both the tanks are not able to meet designed irrigation demands. Irrigation demands have been estimated with the changes in cropping pattern and irrigation area along with the assessment of groundwater availability. Though tanks are designed to supply irrigation water in non-monsoon season for Rabi crops only, but for better profitability, it may be feasible to grow some cash crops in Kharif season in Silarkhedi Tank command. Accordingly, a new cropping pattern along with possible coverage areas under respective crops is suggested for cultivation in Kharif season in the command area of Silarkhedi tank.