3.1. Data collection This study has been carried out on the basis of available secondary data and field data. The secondary data for the study were collected from different sources such as Bangladesh Agricultural Research Council (BARC), the World Bank (WB), National Minor Irrigation Development Project (NMIDP), Bangladesh Agricultural Research Institute (BARI) and the Department of Agricultural Extension (DAE) of Bangladesh. Data related to natural hazards were collected from the publication A Vision for Agricultural Research 2020 by BARC (2000). Data about the area covered by different irrigation equipment, expressed in percentages, has been collected from WB and NMIDP reports under Agricultural Policy Issues in Bangladesh. Data on the total number of irrigation equipment, the gross irrigated area and the total volume of irrigation water withdrawn are taken from the BARI annual reports. The data on annual crop production and its percentage, which was hampered because of the lack of supplementary irrigation, were collected from DAE reports.
3.2. Economic benefit computation The total loss of water has been computed by subtracting total crop consumption of water from the volume of water lifted. The actual volume of water required for irrigation was calculated through the computation of crop consumption of water, while the volume of wastewater was computed by subtracting this volume of water (crop consumption) from the total water lifted. Taking account of the recommendation by BARI, 1997, 52% of wastewater may be saved if proper irrigation practices are followed. An area of 1.82 Mha may be irrigated with the wastewater saved. 5,185 m3 of water is recommended for one hector of land for crop growth and it costs US$77. Thus an economy of US$140 M may be made by using wastewater, which is saved. The calculations of the economic benefits from proper irrigation management are done on the basis of expenditure that may be saved by using wastewater. The wastewater to be saved would be used for irrigation of an additional area of about 1.82 Mha, which would provide about 9.97 MMT of additional crops (Table 4). The cost of production per ha is US$268, the yield per ha is 5.48 MT and the price of one MT is US$103.4. So, a net financial benefit is computed to be US$543 million. About 30% of Aman rice (summer-type rice) that is, about 3.3 MMT (Table 5) is affected owing to lack of supplementary irrigation. By carrying out supplementary irrigation for only of 45% of affected Aman (summer-type rice) rice, an additional Aman rice yield of about 1.485 MMT may be grown and a total financial benefit of about US$155 million may be accrued. The price of 1 MT rice is US$103.4.
Irrigation equipment like the deep tube-well (DTW), the shallow tube-well (STW) and the low lift pump (LLP) are diesel driven and at present operate with an efficiency of about 60%, which is quite low. The operation of irrigation equipment may be improved at least by 20% by saving the cost of operation and maintenance, fuel, man power, and so on, and a total saving may be achieved of about US$107.6 million (Table 6). The operation cost has been quoted from a NMIDP report. Bangladesh has natural and man-made water bodies of area about 334,649 ha. Silting up of these water bodies is gradually reducing their capacity for preserving water. Preserving capacity of water bodies is 6,693 Mm3. It is possible to use about 50% of this capacity, that is, 3,346.5 Mm3 of water, bringing the area under irrigation to about 0.64 Mha through excavation. The area brought under irrigation may provide a yield of about 3.5 MMT, which in return may provide a financial benefit of about US$362 million. The data are taken from BARC (2000).
Minor irrigation systems dominated by the private sector do not follow any proper engineering rules. As a result, the minor irrigation systems incur losses. The Workshop on Agricultural Mechanization in BARC in 1992 showed that owing to the unplanned installation of minor irrigation equipment (Table 8), the efficiency of the system, at present, is only 57%. If it is possible to achieve an increase of efficiency of only 20%, then only the economy of diesel and electric energy may save about US$38 million in this sector
Government policies, as well as interventions, are necessary to achieve economic benefits from the above-mentioned activities. So, for successful implementation of improved irrigation management, it is proposed that one agricultural engineer together with one assistant officer be posted in each Upazila (police station, a sub-unit of a district). The salary of one engineer and one assistant officer with other expenditures, for every Upazila (working station), would come about US$1.74 million only. Expenditure costs for one engineer and one assistant officer are calculated considering Bangladeshi salaries. Office expenditure is taken as 50% of salary. Thus the expenditure for one station is calculated. Afterward, the total expenditure, considering 460 stations, for carrying out management operations is calculated.
Finally, the assessment of the economic benefit is summarized, showing all economic benefits to be derived through various activities.