Evaluation of Hydraulic Performance On Lower Areb Small Scale Irrigation Scheme Amhara, Ethiopia

This study was conducted in the Lower Areb small-scale irrigation scheme for one crop 25 season from March to May 2018 to evaluate the hydraulic performance of the scheme by 26 estimating the hydraulic performance indicators, physical was evaluated by estimating adequacy, efficiency, dependability, and equity indicators at 32 nine selected offtakes; three each at the head, middle, and tail reaches of the scheme. The 33 physical performance and maintenance indicators were determined using the irrigation 34 ratio, the sustainability of the irrigated area, the effectiveness of infrastructure, and the 35 water surface elevation ratio. The data were analyzed by using CROPWAT 8.0, ARC GIS 36 10.1 software, and Microsoft Excel 2013. The overall average values of adequacy, 37 efficiency, dependability, and equity were found to be 0.89. 0.91, 0.096 and 0.07 38 respectively. Therefore, dependability, equity, and efficiency were under good condition 39 and adequacy was under fair condition. The irrigation ratio and sustainability of irrigated 40 areas were 54% and 123% respectively. The effectiveness of infrastructure and water 41 surface elevation ratios were 73.33% and 94% respectively.

Performance assessment is used to identify the present status of the performance of the 75 scheme using different indicators. These indicators evaluate the spatial and temporal 76 distribution of the required and delivered water for the given irrigation scheme (Tebebal ,77 2015) The in-situ measurement can provide a quantitative assessment of overall system 78 performance. Therefore, this study was intended to evaluate the hydraulic performance of 79 the irrigation scheme with irrigation service at Lower Areb small-scale irrigation scheme, 80 Ethiopia.  Geographically the project area is located at 11 0 30′ 00″ to 11 0 36′ 00″ latitude and 36 0 48′ 87 00″ to 37 0 00′ 00″ longitude. The elevation in the watershed varies from 1847 masl on the 88 axis of the headwork to 2200 masl on the upper ridge. The headwork structure is located at 89 an altitude of 1860 masl. 90 The location map of the Lower Areb small-scale irrigation scheme is shown in Figure 1.

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The project area is characterized by "Woyenadega" agroecology based on the elevation of 115 the area. The rainfall pattern of the project area is unimodal type in which one main rainy 116 season occurs during July to August. The average monthly rainfall in July and August is 117 360.8mm and 378.3mm respectively. The mean annual rainfall of the area is 1630.2mm. 118 The prevailing temperature considerably influences the selection of crops and their growing 119 periods. The mean maximum and minimum annual temperature are 25 0 C in April and 9.3 0 C 120 in January respectively. The mean monthly and sunshine hour duration of the project area   Conducting in-situ measurements in all canal branches and for each offtake was a difficult 135 task due to its time-consuming and cost-effectiveness. Therefore, the representative 136 locations for data collection were selected through a stratified sampling technique. The 137 measurements of delivered discharge in the command area were made at 9 selected offtakes 138 out of 12 total offtakes. Three offtakes were selected at each of the upstream, middle, and 139 downstream reaches of the main canal which grow a similar crop in all fields per offtake. 140 In the present study, nine tertiary offtakes which grow similar crops per tertiary offtake   144 This study was carried out for one irrigation season, from March to May 2018. The choice 145 of selecting this period for the study was because there was hardly any rain during the 146 period and almost all field crops were irrigated. Both quantitative and qualitative data were 147 collected from primary and secondary sources. The primary data were collected from direct 148 field measurements, field visits, and laboratory analysis. The secondary data were obtained 149 from the north Achefer district agricultural office, Amhara National Regional Bureau of 150 Water and Irrigation energy, regional meteorological agency, related journals, published 151 and unpublished thesis, and FAO documents.  The discharge measurements were one of the reliable data to evaluate scheme performance 160 indicators. The water flow velocity and water flow depth of the offtakes were measured 161 using the current meter and calibrated 3-inch Parshall flume. 162 2.6.1. Velocity measurement using current meter 163 The current meter is the most widely used device to measure the velocity of water flow.

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The velocity at the selected points of the reach was measured using SEBA-universal current V is the water flow velocity (ms -1 ).

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The canal dimensions were measured using a tape meter. The canal discharge was 187 calculated using Equation 2.6.    Table 1.  Adequacy is a measure of the delivery of the required amount of water for optimal plant 298 growth. It relates the actual delivery to the desired amounts of water needed for crop 299 irrigation at delivery points in the system. Adequacy is the ratio of water delivered (QD) to 300 water required (QR) for a single offtake. The adequacy was determined for service area (R) 301 represents the sub-region of the system whose performance is determined and averaged 302 over three months of the study period (T) from March to May 2018 represents the period 303 in which system performance was determined of the entire irrigation system. The adequacy 304 was evaluated as the spatial variation of adequacy levels at the head, middle, and tail 305 offtakes and the temporal variation of adequacy levels throughout the three months using where: with water requirements and if the system is supplying more than the water requirement, it 317 indicates the non-conservation of the resources. Efficiency is determined as the ratio of 318 required to delivered flows (QR/QD). Efficiency was determined for the head; middle and 319 tail reach off takes using Equation 2.14.
Where: 322 PF = efficiency indicator over an area R and period T.

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It is an indicator of the degree of reliability of water delivery. It is the degree of temporal 325 variability in the ratio of the amount delivered to the amount required ( ) over a region. 326 This performance measurement indicates the uniformity of QD/QR over time. An irrigation 327 system that achieves almost steady water distribution is considered to be dependable when 328 the value of PD approaches zero and PD values close to 1.0 indicate serious unreliability 329 of water distribution. This indicator may be estimated using Equation 2.15.
Where: 348 PE = equity indicator over an area R for a period of T, and 349 CVR = spatial coefficient of variation of the ratio QD/QR over a region R.

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The value of the spatial coefficient of variation was determined by the ratio of the spatial 351 mean over standard deviation. The spatial mean can also be computed by the average ratio 352 of QD and QR values for nine selected offtakes.
The actual irrigated area and initially irrigated area were obtained from district experts, the 364 Water user association, and Development agents. The actual irrigated areas for the 365 irrigation scheme were determined in two ways, the first was by collecting the list of 366 irrigation water users along with their irrigated land holdings compiled by the scheme water 367 user associations and the second was, by using GPS conducted to determine non-irrigated 368 lands, residential areas, and grazing land. The net irrigated land area was then determined 369 as the difference between total command areas and the sum of all non-irrigated land areas 370 within the command. 371 2.9.2. Irrigation ratio (IR) 372 The irrigation ratio shows the degree of utilization of the available irrigable command area 373 for irrigated agriculture for a particular production period. The value of IR was estimated 374 using Equation 2.18.
The irrigable area of the irrigation system was determined by locating GPS to the boundary 377 of the irrigable area.

Maintenance indicators 379
Appropriate maintenance enables the keeping of water control and distribution 380 infrastructure in good working condition to maintain the design water level. The hydraulic 381 performance of the scheme could also be evaluated through maintenance performance  TO1, TO2, TO3, TO4, TO5, TO6, TO7, TO8, and TO9 were 3, 4, 5, 3, 4, 3.5, 4, 3.5, and 5 411 ha respectively. The overall mean required discharge of the nine tertiary off-takes during 412 the study period was 3.01l/s. It may be observed from Figure   The temporal average delivered discharge at the head flow was high. This was because due 448 to more area coverage and there was adequate water as compared to middle and tail reach.

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In the middle and tail delivered discharge was low as compared to the required discharge overall mean delivered flow was slightly lower than the overall mean of required flow.

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There may be due to the shortage of water, failure of the intake structure, canal 455 sedimentation problem, and maintenance problem.     May as per ranges of water delivery performance standards given by Molden

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Efficiency was calculated by using Equation 2.14 for the selected nine tertiary offtake problem-related to operation and management. Whereas, the spatial efficiency during April 519 was very high, during this month the crop stage was the developmental and mid-stage, at 520 this stage all crops need more water than the delivered amount of water. Therefore, there 521 was high water consumption, and the irrigation users used water efficiently. According to 522 the ranges of water delivery performance standards given by Molden and Gates (1990)   computed values of dependability are given in Table 5. The temporal coefficient of 541 variation for different offtakes is shown in Figure 8. performance standards given by Molden and Gates (1990) in Table 1. The remaining 552 offtakes were grouped under a good performance level in the reliability of water delivery.

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Thus the water user associations in tertiary offtakes TO1, TO6, and TO7 did not follow 554 timely and effective water distribution. While the water user association committee 555 followed timely and effective water distribution in tertiary offtake TO2, TO3, TO4, TO5, 556 TO8, and TO9.

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The temporal average values of coefficient of variation at the head, middle and tail reach 558 were 0.085, 0.093, and 0.11 respectively. It may be observed from these value the 559 coefficient of variation at tail reaches is as high as compared to head and middle reaches.

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Thus the farmers at tail reach were not receiving the delivered water timely and in the 561 required amount due to unfair water distribution. While the irrigation users located at head 562 and middle reaches abstracted more water compared to the irrigation users at tail reach.

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The degree of spatial variation of hydraulic performance for nine selected tertiary offtakes 578 over three months is presented in Figure 9. It may be observed from Figure 9 that the spatial coefficient of variation was higher during 582 March and April due to the unfair share of irrigation water in each offtake structure. While 583 during May spatial coefficient of variation was less in each offtake structure distributed 584 irrigation water. According to standards as proposed by Molden and Gates (1990)   The sustainability of irrigated area (SIA) of the present study was estimated by using 594 equation 2.17. The estimated value of SIA for two irrigation seasons is given in Table 6 595 and the graphical variation is shown in Figure 10.

Irrigation ratio 622
The irrigation Ratio for the present study was estimated using Equation 2.18. The estimated 623 value of IR is given in Table 6 and the graphical variation of irrigation ratio during two 624 irrigation seasons is shown in Figure 10. It may be observed from Table 6, that the irrigated structures at the tail reach of the irrigation scheme. It may be seen from the above Table 6 633 that the difference in the designed command area and the irrigable area was 14 ha. The 634 potential of the irrigable area was greater than the potential of the scheme. The scheme was 635 designed to irrigate only 65 ha of land.        Table 9. Performance evaluation of irrigation schemes has especially been an important and active 724 field of research during the last few decades. It is used to identify problems and 725 understanding how the system can be effectively implemented to improve the system 726 performance.

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The overall average irrigation water required for the selected nine tertiary offtakes for the 728 selected crops such as maize, onion, and potato grown in the command area as compared 729 to irrigation water delivered was more during April but less during March and May. The 730 water delivered by the canal was more than the crop water requirement at head and middle 731 reach but less at tail reach. The temporal and spatial variations of canal water supply in 732 each tertiary offtake were due to weak management of WUAs in irrigation scheduling, 733 cleaning canals sedimentation and weeds, water losses in canals, and damaged water 734 control structures.

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The Hydraulic performance of the irrigation scheme was evaluated using adequacy, 736 dependability, efficiency, and equity hydraulic performance indicators. The hydraulic 737 performance of the irrigation scheme as compared to standards proposed by Molden and 738 Gates (1990) was found to be good for dependability, efficiency, and equity, but fair 739 inadequacy. Although the overall hydraulic performance of the irrigation scheme was and moral support.

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Competing interest 773 The authors declare no competing interests.