Buried pipe systems for irrigation in Bangladesh

A study of eight cement concrete buried pipe schemes in Bangladesh was carried out during 1989-91 to evaluate both technical and management performance. Leakage through joints and pipe walls, averaged 0.9 leaks per 100m of pipeline, while 42% of outlet valves were observed to leak. Conveyance losses within the pipelines averaged 0.33 lps/100m by the tank test method and 0.69 lps/100m by inflow-outflow method, with earth channel losses averaging 7.69 lps/100m by the inflow-outflow method. Machine spun pipes performed better and "plain end pipe jointing" was found appropriate. Measured head losses for different pipe sizes and pump discharges were found com­patible with theoretical values when using the Colebrook­White Equation with Ks = 0.6 mm. Low pump discharge (60% of design), low periods of pump operation (12% of advised), small command areas (42% of intended) and low yields of irrigated crops were commonly observed. Sea­sonal repair and maintenance expenditure on pipeline sys­tems varied from Tk 4.64/ha to Tk. 127.19/ha, with the average of Tk. 54.06/ha being only 18% of expenditure in earthen channels. Poor farming as well as water manage­ment practices contributed to poor levels of irrigation per­formance. Farmers' cooperatives were found either not to be functioning or operating only very poorly, and many insti­tutional problems existed. Pipe systems are more economical than channel systems when the initial cost is affordable. There is however consid­erable potential to increase the net returns from buried pipe schemes through more efficient utilisation.