Abstract:
A study was conducted to assess the impact of improved distribution systems of six selected shallow tubewell (STW) irrigation schemes in Paikgacha upazila of Khulna district. Three of the shallow tubewell irrigation schemes has compacted earthen canal and the rest has lined canal. The impact of improved distribution system was assessed by comparing the performance of the schemes under pre and post - improvement situations. The indicators used for performance comparison are- duty of water, water use efficiency, overall irrigation efficiency and cost effectiveness of the improvement works. The pre improvement (2006 - 07) problems of the selected schemes were: more loss of irrigation water, fuel and oil cost or electric bill was high, production cost was more due to higher irrigation cost and more land required to make traditional earthen canal. The distribution system was improved during the month of December, 2007. For improvement of the system, the bottom of the earthen canal was compacted properly with 8 - 12 cm of earth filling (clay soil) by two steps. A sand layer of 2.5 cm was placed on the canal bottom. Then pre-cast slab was installed in the canal maintaining proper alignment and slope. For compacted earthen canal, a layer of clay with cowdung was put on the bottom and sides of the canal after complete compaction.
The comparative assessment revealed that the duty of water increased by 10% for lined canal distribution system and 7% for compacted earthen canal distribution system with respect to traditional earthen canal distribution system. Water use efficiency increased by 14% for lined canal distribution system and 10% for compacted earthen canal distribution system compare to traditional earthen canal distribution system.
The average overall irrigation efficiency under pre and post improvement situations for the selected lined canal distribution system were 29% and 33%, respectively. It was increased by 4% with respect to traditional earthen canal distribution system. The
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average overall irrigation efficiency under pre and post improvement situations for the selected compacted earthen canal distribution system were 29% and 32%, respectively and it was increased by 3% compare to traditional earthen canal distribution system.
The benefit - cost ratio of the pump owners increased by 6% for lined canal distribution system and 10% for compacted earthen canal distribution system with respect to traditional earthen canal distribution system. The average value of benefit - cost ratio for lined canal under post improvement situation 1.28 was found to be less than the value for compacted earthen canal 1.40. This is due to higher initial cost of the lined canal system compare to compacted earthen canal system. The improvement of the system does not have any impact on the profitability of the farmers. This is because the farmers pay the same rate of irrigation charge both before and after the improvement of the systems.
