The Department of Agricultural Extension is involved in experimentation of improved water distribution system in order to develop different low cost canals for minor irrigation schemes. As of now, the DAE through its AETEP has implemented several new technologies in respect of lining of irrigation canals. These linings are superior to the traditional earthen canal, especially in respect of efficiency. In this study, the linings recommended by AETEP were constructed and field tested in order to assess their impacts over the traditional earthen canals. The study was undertaken in 2010-11 Boro season at three upazilas: Manikgonj sadar of Manikgonj district, Dhamrai of Dhaka district and Mithapukur of Rangpur district. Nine improved earthen canals, three pre-cast lined canals and six existing earthen canals under STW were selected for field study.
Method of measurement of conveyance loss
In this study, inflow - outflow method was used for conveyance loss measurement . The inflow - outflow method was widely used by most of the researchers in Bangladesh for its simplicity and accuracy (Dutta, 1991; Sattar et al ., 2002; Maniruzzaman et al ., 2002). This method is very suitable to measure the canal water loss than, unlike po nding method, the irrigation can continue while the discharge measurements are taken. The results obtained by inflow - outflow method are more reliable than the other (Pond method and Seepage Meter method) methods (Shahid et al ., 1991). Consequently, the inflow - outflow method was employed for this study. There are various types of water measuring device by which flow of water can be determined. In this study, cut - throat flume was used for discharge measurement. The most obvious advantages of cut - throat flu me are its economy, accuracy and field suitability.
Determination of conveyance loss
Conveyance loss of water was calculated as: CL = {(Q1 - Q2)/L} X 100 ... ... (1)
where, CL is the conveyance loss in the canal in lps/100m, Q1 is the flow at the inlet in lps, Q2 is the rate of flow at the outlet in lps and L is the distance between the two canal sections in m.
Water loss of respective canal was measured with cut - throat flume under two conditions. These were: (i) natural condition (existing earthen ca nal), and (ii) improved condition (after compaction and lining)
Land occupied by canal
In Kharif season, most of the farmers leveled down their earthen canal to grow Aman paddy. They generally do not provide supplementary irrigation to Aman crop. B ut, when improved earthen canals are constructed, they are not leveled down, as such; the land required for the construction of the canals goes out of production. To measure the area of land occupied by canal, length and width of the main canal were measured in consultation with the scheme manager and pump operator. 2.4. Economic analysis An economic analysis was carried out for the distribution system of irrigation water in order to ascertain the profitability of the lining technology. For this purpose, discounting method of the appraisal technique was used. By discounting, future cash flows are reduced to their present worth. For measuring the relative worthiness of the system, three alternative discounted measures namely, net present worth (NPW), benefit cost ratio (BCR) and the internal rate of return (IRR) were used.
Field survey
Field surveys were carried out in each of the upazilas to assess the impact of water saving on command area development and the acceptability of lined canal technology by the farmers. Participatory rural appraisal (PRA) approach was used for collection of socioeconomic data. Focus group discussion (FGD) was used for socio-economic data and information collection. Each FGD involved 9-11 persons. Average age of the farmers was 34 years and all of them were male. For collection of socio-economic information, 9 (nine) FGDs were conducted in the selected study areas. Three FGDs were conducted with the pump owners and other six with the irrigation farmers.