Evaluation of four farmer-managed deep tubewell irrigation schemes : case studies

Abstract

A bnsc-linc study was undertaken in 1988-89 irrigation season on the Tour deep tubcwcll schemes in Dhaka and Manikganj districts to identify the problems constraining the command area development. Plausible solutions to the priority problems that are technically feasible and economically viable were developed and implemented. Pump discharges were 51 to 62 Ips against the design discharge of 56 Ips and drawdown observed varied from 5.06 to 7.21 m. Pumping hour (14.7 to 17.5 hrs / day) was good. But pump operation per unit area (89.9 to 99.5 hrs/ ha) channel density (91 to 153 m/ha) and area occupied by the channels (1.84 to 3.9%) were considerably high). Channels were constructed with inadequate capacity, insufficient freeboard, uncompactcd channel banks and irregular channel bed slope at all schemes. Irrigation application was not based on crop water requirement at any of the sites. Over irrigation (mostly at the head end) as well as under irrigation (mostly at tail end) were observed existing together in each scheme. At none of the sites block rotational irrigation was practiced. Daily crop water use was found 8 to 12 mm at the peak period. Rainfall varied from 70 to 140 mm during the boro season. Lower ailc heights (4 to 11cm) were observed which were insufficient for ponding water. Night irrigation was practiced at all sites with insufficient supervision and care. Command area per unit of pump discharge varied from 0.31 to 0.41 ha (about 57 to 75% of the potential command area). Conveyance losses were found 7 to 11 Ips/lOOm of channel length and conveyance efficiency ranged from 43 to 68 percent. Inequity of water distribution was observed at all schemes (1.7 to 23) and adequacy of water supply varied from 0.86 to 235.