Comparative study on command areas of shallow and deep Tube wells in irrigation development

Abstract

The innovations in minor irrigation technology like deep and shallow tubewells (DTW and STW) have led to a rapid increase in the irrigated area. With time, the number of irrigation equipment has increased but the area coverage per STW has decreased. As STWs have played a dominant role in the expansion of groundwater development, the underutilization of STWs is matter of great concern. The major objective of this study was to examine the factors responsible for the decreasing and increasing trends of command area of STWs and DTWs through extensive field measurements and famers’ and pump operators’ surveys (FGDs). The performance of 20 diesel operated and electrified STWs and 8 DTWs were studied in Digulkandi and Daulabari Unions of Ghatail Upazila of Tangail district. The average command area of STWs decreased from about 4 ha to 2.4 – 2.9 ha, depending upon the source of energy and water pricing system. Two different irrigation pricing systems were prevalent in the two study areas for STW irrigation. In Digulkandi Union, the ¼ crop share system was practiced for diesel and electricity operated STWs, while in Daulabari Union, area based cash payment system was practiced for electricity operated STWs. The average discharge of electricity operated STWs was higher than diesel operated STWs mainly because the former were recently electrified with new engines (5 or less years old). With similar water pricing system (¼ crop share), the farmers of electricity operated STWs used 74% more water than the diesel operated systems. But, the farmers with area based pricing system and electrified pumps used 44% more water than diesel operated ¼ crop share based STWs, mainly because electricity is cheaper than diesel and as a security against power interruption. The STWs operated with either diesel or electricity under ¼ crop share system are much more profitable than the electricity operated STWs under area based pricing system. Although the farmers of ¼ crop share system paid a much higher price of water than the crop share based system (Tk. 23,712/ha compared to Tk. 9880/ha), the crop share system has prevailed because the farmers do not have to pay any cash for the water, there is adequate water supply as the pump owners also want to ensure a high yield and there is less conflict between the pump owners and the farmers regarding water distribution. The command area of STWs was not dependent on the pump discharge or the total volume of water pumped but depended upon socio-economic factors. The main reasons for the continued decreasing trend of command area of STWS in the study area were privatization of irrigation equipment, low cost pump and availability of spare parts at local market, high irrigation water price, conflict between pump owner and farmer due to water distribution, multiple uses of STW engines, available foreign currency etc. Some positive impact were also found due to decreasing command area of STWs such as increase in irrigated area (even though not proportional to the increase in number of STWs), less conflict between farmer and pump owner, increased employment opportunity in rural area, etc. Although there was no significant difference in yield across pricing system and source of energy (average of about 5.2 t/ha), the water use in STW systems varied from 1266 to 2207 mm, signifying the importance of improved management in irrigated Boro rice. The command area of the DTWs has increased mainly because of the PPP (operation by the farmers and the maintenance by BADC) and the role of ‘Upazila Irrigation Committee’ in DTW installation. The average water productivity in DTWs (5.75 kg/mm) is much higher than the highest average water productivity of the STWs (4.06 kg/mm) because of improved conveyance system (lined canal and buried pipe) and time based water pricing system. In order to stop the decreasing trend of command area of STWs, the role of the ‘Upazila Irrigation Committee’ in installing new STWs must be made mandatory. The committee will ensure the command area and the spacing between wells (according to Groundwater Ordinance of 1985) before giving permission for installing new STWs. The present irrigation water price is highly profitable for the pump owners/operators (specially in ¼ crop share system) and measures should be taken to implement a fair pricing system for the farmers (Tk. 6587/ha as suggested by BADC) through the `Upazila Irrigation Committee’.