Performance evaluation of some selected deep and shallow tubewells in irrigation development

Abstract

Performance evaluation of five Deep Tubewells (DTWs) and ten Shallow Tubewells (STWs) of Rajbari district has been carried out in the present study. The broad objective of the study was to evaluate the performance of these schemes using some selected standard indicators. The performance indicators used in this evaluation have been broadly classified into three groups: hydraulic indicators, agricultural indicators and socioeconomic indicators. For the quantitative assessment of the hydraulic indicators, field measurements were taken during 1998-99 Boro season. Questionnaire survey of farmers and pump owners was carried out for the quantitative as well as qualitative assessments of agricultural and socio-economic indicators. Results of the analyses show that delivery performance ratio of DTWs is 0.93 and that of STWs is 1.21. The average discharges of both DTWs and STWs (53 l/s and 17 lis, respectively) were greater than the respective national averages (46 l/s and 12 lis). The average STW discharge was even greater than the target discharge (14 lis) as most of the STW owners used strainers of larger diameter (greater than 10 cm) and motors/engines of higher capacity (greater than 6.0 bhp). OTWs and STWs have water delivery performance of 0.85 and 0.98, respectively. Though the seasonal operating hours of both DTWs and STWs (1127 hours and 1054 hours, respectively) were below their respective national averages (1223 hours and 1216 hours, respectively), yet the actual command areas (23.7 ha and 6.04 ha, respectively) were above the respective national average command areas (23.1 ha and 4.3 ha, respectively). This has happened because the actual volumes of abstraction, 213838 m3 for OTWs and 60360 m3 for STWs, were more than the national averages by 5.6% and 13%, respectively. No relationship was found between pump discharge and command area. But, a good correlation was found to exist between the volume of water lifted and the command area (r2 is 0.96 for OTW and 0.90 for STW). The slope of the regression line (command area versus volume) for DTWs was found to be 1.5 times of STWs. This indicates that increase in command area per unit increase in volume of water withdrawl was more for OTWs compared to STWs. In the unlined portion of the OTW canal, the average conveyance loss was 6.5 m/day and it was 1.4 m/day for the lined portion. In STWs which are unlined, the average conveyance loss was 4.1 m/day. In the present study area, irrigation canal density (45.23 m/ha and 55.13 m/ha in OTW and STW schemes, respectively) was very low compared to past studies. The average land preparation requirement was found to be 108 mm in the present study compared to around 200 mm of past studies. The seepage and percolation losses in the farmers' fields of the study area were found to be 5.3 mm/day. Dependability of water deliveries of STW and OTW schemes (0.85 and 0.79, respectively) was satisfactory during 1998-99 Boro season. For STWs, significant improvement has occurred in the utilization of irrigation water per Boro season in the present study area (999mm) over national average (1222 mm). But for DTWs, this has remained near the national average (902 mm in the present study versus 877 mm, the national average). Equity in water delivery, was not ensured in both DTW and STW schemes. Inadequacy in lengths, maintenance and sections of irrigation canals, frequent power disruptions and presence of non-irrigated and non-rice fields, even fallow lands, around project periphery were mainly responsible for this lower equity. Agricultural performance, evaluated in terms of irrigated area performance (0.79 and 0.76 for OTWs and STWs, respectively), yield performance (1.16 for both DTWs and STWs) and production performance (0.92 and 0.87 for OTWS and STWs, respectively), was almost the same for both OTW and STW schemes and was greater than the national averages. The average yields of HYV paddy of the study area are much higher than the national average yields during Boro season. Total financial viability of OTW and STW schemes (3.23 and 3.61, respectively) was quite high during 1998-99 Boro season. But, the profitability of farmers was 1.06 and 1.05 for OTWs and STWs, respectively during the same period. Fee collection performance was exactly 100%.