EVALUATION OF STW EQUIPMENT CHARECTERISTICS AND STW IRRIGATED SCHEMES USING PERFORMANCE INDICATORS
6.3 DATA ANALYSIS, RESULT AND DISCUSSIONS
6.3.1 Technical Characteristics of STWs irrigation Equipment
6.3.1.6 Command area (C/A) under different engine capacity
Average Command area under different engine capacity was shown in Table 6.3. Table 6.3 showed that engine capacity ranged from 6.5 to 7.5 HP belonging higher C/A comparatively others and field survey data revealed that most of these engines are electrically operated providing with partnership. Mandal (1997) also stated that small farmers’ share of STW
0 10 20 30 40 50 60
China Japan England Unknown
% of Engine/motor
Name of Country
Country wise share of engine/motor
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ownership has increased significantly over the years in Bangladesh. Those farmers who were unable to get electric connection to their engine due to high charge of electric connection fee and also not potential in social, they were running their business by low capacity engine (5.0 to 6.0 HP) comprising less average command area.
Table 6.3: Average Command Area (C/A) under different engine/motor capacity.
BHP range (HP) Average C/A (ha)
5.0-6.0 (22) 3.55
6.5-7.5 (20) 4.25
8-12 (5) 3.75
Unknown (3) 2.72
Note: Figure in parenthesis indicates number of engine/motor.
(Source: Field survey, 2015-16) 6.3.2 Technical Performance of STWs 6.3.2.1 Hydraulic Performance
6.3.2.1.1 Delivery performance ratio (DPR)
Average discharges of DOS and EOS during 2016 Boro season (January-May) were 15 and 16 l/s, respectively. Target discharge of a tubewell was the standard design discharge of its pump and was taken as 14 l/s for STW (DAE, 1994). The average DPR was found to be 1.07 for DOS and 1.14 for EOS schemes. National average discharges of DTWs and STWs were 46 l/s and 12 l/s, respectively (MPO, 1985). This indicates that the present average discharges of both DOS and EOS of the study area were well above the then respective national averages.
The average pump discharge of the 12 STW was 15.5 liter/sec measured in January-May, 2016.
The discharge range of 12 STWs was 10.00 to 26.72 liter/sec in the study area based on pump- engine capacity. Both discharges were similar due to similar characteristic aquifer in the study area, which was discussed in chapter 4. Though same BHP of engine and same diameter of installation pipe, discharge may be varied due to strainer length and position (vertically), type of aquifer, height of drawdown etc. To determine pump discharge volume method was followed1. The rate of flow was measured by the following formula:
Discharge rate (litres/sec) =
fill to required Time
container of
Volume
1 Firstly, we tried to measure pump discharge using X-Y coordinate method, but it was not possible due to wide spreading of water from the delivery pipe. Then we tried to measure pump discharge by Velocity-Area method. Due to low water depth and narrow channel, Velocity-Area method also was not appropriate at the field condition. For this reason, we measured pump discharge by volumetric method. We used a 240 liter capacity of container and stop watch to calculate time elapsed to fill the container. Pump discharge of 12 STWs were measured in the study area.
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Figure 6.2: Showing measurement of pump discharge in the study area.
6.3.2.1.2 Water delivery performance (WDP)
Average seasonal operating hours of DOS and EOS were found to be 1127 h and 1054 h respectively, in the study area. Earlier, the average seasonal operating hours were 1223 h for DTWs and 1216 h for STWs (MPO, 1985). This indicates that averages of the seasonal pumping hours of both DOS and EOS of the study area were below the then respective national averages by about 100 h and 160 h, respectively. WDP was found to be 0.85 and 0.98 for DOS and EOS, respectively. WDP of EOS was better than that of DOS because the actual discharge of EOS was higher than its target discharge.
6.3.2.1.3 Conveyance loss ratio
Conveyance loss in the irrigation canal depends upon whether it was lined or unlined. In STWs (both for DOS and EOS), which were unlined, the average loss per 100 m was 2.75 l/s (18.33%
of the discharge). In a study, Dutta (1993) found an average conveyance loss of 4.5 l/s per 100 m length of canal for four DTWs and 2.6 l/s for four STWs. Thus, the average conveyance loss found in the present study was comparable with that of the past studies.
6.3.2.1.4 Overall reliability
Overall reliability of water deliveries was found to be 0.86 and 0.82 for DOS and EOS, respectively. So, in both the DOS and EOS schemes of the study area the volume of water supplied and the duration of the supply are close to their respective targets and the schemes can be considered as reasonably dependable.
6.3.2.1.5 Equity
To evaluate the equity of water deliveries, three farmers from head, middle and tail ends of each irrigation scheme were interviewed three times during 2016 Boro season (January-May) regarding the availability of water in terms of depth. The equities thus obtained are given in
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Table 6.4. Equity or spatial uniformity in water delivery was not met for both DOS and EOS schemes. This happened because of frequent electric disruptions, inadequate canal lengths and inadequate maintenance of irrigation canals (lack of timely cleaning of vegetation from supply canals, non-closing of rat holes and cracks that developed in the canal embankments, inadequate canal section resulting in overtopping of embankment, etc.), which hampered the supply of water to the tail end farms. The average irrigation canal density was more or less similar which 58 m/ha for DOS and 60 m/ha for EOS. Dutta (1993) found an average canal density of 190 m/ha for DTWs and 206 m/ha for STWs.
Table 6.4: Head:tail and middle:tail equities of DOS and EOS schemes Type of tubewell Tail:head equity Tail:middle equity
DOS 0.50 (0.45–0.57)* 0.52 (0.50–0.54)
EOS 0.45 (0.36–0.54) 0.55 (0.53–0.57)
*The values within the brackets indicate range.
6.3.2.2 Agricultural performance