Performance of concrete buried pipe distribution systems for surface irrigation under farmers' management in Tangail, Bangladesh

The operation of irrigation systems on eight deep tubewells in Tangail district, Bangladesh, was monitored from 1989 to 1991. These systems used buried non-reinforced concrete pipe to distribute water from deep tubewells and irrigate diversified crops during the dry season. The potential of buried pipe networks for surface irrigation at low heads is documented, and performance under farmers' management is outlined in this thesis. For example, the utilization rates of all the tubewells were disappointing, averaging 3.5 hrs/day at a discharge of 32.5 lis compared to the design of 56 l/s. The irrigated area averaging 16.6 ha was typically less than half of the design (40 ha). The reasons for this poor performance were found to be a combination of social, managerial and agro-economic factors. Leakage through joints and pipe walls averaged 2 leaks per 100 m of pipeline, while 42% of outlet valves were observed to leak. Conveyance losses within the pipelines averaged 0.7 1/s/100 m with earth channel losses averaging 7.7 1/s/100 m. Measured head losses for different pipe sizes and pump discharges were found compatible with theoretical values' when using the Colebrook-White Equation with Ks=0.6 mm. Low pump discharge (58% of design), low periods of pump operation (12% of advised), small areas (42% of intended) and low yields of irrigated crops were commonly observed. Poor farming as well as water management practices contributed to poor levels of irrigation performance. Farmers' cooperatives were found not efficient and many institutional problems existed. Buried pipe systems and open channel systems were compared in terms of seepage loss and costs. It was found that buried pipe systems were more economical than open channel systems. There is however considerable potential to increase the net returns from buried pipe schemes through more efficient utilization. Possible improvements are discussed in this thesis. These include moving systematic irrigation of fields fed by the same branch, instead of the current erratic distribution of water under the farmer's fuel system.