evaluation of irrigation canal maintenance according to roughness and active canal capacity values
TRANSCRIPT
Evaluation of Irrigation Canal Maintenance according toRoughness and Active Canal Capacity Values
Erhan Akkuzu1; Halil B. Unal2; Bekir S. Karatas3; Musa Avci4; and Serafettin Asik5
Abstract: This work assesses the state of maintenance of the concrete-lined trapezoidal canals of the Menemen irrigation system at theend of the Lower Gediz Basin according to the values of roughness �n� and active canal capacity �ACC�. The study was carried out ontwo main canals, five secondary canals, and 12 tertiary canals at 45 measurement points. Average values of n and ACC were found to be0.023 and 69%, respectively, for the main canals, 0.018 and 93%, respectively, for the secondary canals, and 0.023 and 81%, respectively,for the tertiary canals. The fact that values of n for the selected canals were higher than projected values and higher than the limit values,which would indicate adequate maintenance, and that the related ACC values were low, indicates that maintenance is insufficient in thesecanals. In order for maintenance work to be carried out more effectively, it may be suggested that new techniques should be applied forcanal linings, which are economical and longer lasting, that farmers who benefit from the system should be given a more active role inmaintenance work, and most importantly, that the associations responsible for maintenance should be supported financially in theseactivities.
DOI: 10.1061/�ASCE�0733-9437�2008�134:1�60�
CE Database subject headings: Water supply; Water resources; Roughness; Irrigation systems; Canals; Hydraulic structures; Turkey.
Introduction
The total agricultural area in Turkey is nearly 28.1�106 ha.When today’s economical conditions and the restrictions of soilfeatures and topography are considered, 25.7�106 ha of this fig-ure can be irrigated. In the year 2005, the irrigated agriculturalarea was 4.9�106 ha, and 94% of this area was irrigated by sur-face irrigation methods. Of this irrigated area, 3.9�106 ha wasopened to irrigation by two government organizations, the Gen-eral Directorate of State Hydraulic Works �DSI� and the GeneralDirectorate of Rural Service �GDRS� �DSI 2006�.
Since the 1950s, the DSI has had a policy of transferring op-eration and maintenance �O&M� responsibility of smaller andmore remote projects to local administrations. However, until1993, the pace of this transfer activity was extremely slow. Withthe introduction of a so-called accelerated transfer program in1993, transfer rates accelerated dramatically �Svendsen and Nott
1Faculty of Agriculture, Ege Univ., 35100 Izmir, Turkey. E-mail:[email protected]
2Associate Professor, Faculty of Agriculture, Ege Univ., 35100 Izmir,Turkey. E-mail: [email protected]
3Research Assistant, Provincial Special Administration, Dept. of Ag-ricultural Services, İzmir–Turkey, Turkey. E-mail: [email protected]
4Professor, Faculty of Agriculture, Ege Univ., 35100 Izmir, Turkey.E-mail: [email protected]
5Professor, Faculty of Agriculture, Ege Univ., 35100 Izmir, Turkey.E-mail: [email protected]
Note. Discussion open until July 1, 2008. Separate discussions mustbe submitted for individual papers. To extend the closing date by onemonth, a written request must be filed with the ASCE Managing Editor.The manuscript for this paper was submitted for review and possiblepublication on September 22, 2006; approved on May 1, 2007. This paperis part of the Journal of Irrigation and Drainage Engineering, Vol. 134,No. 1, February 1, 2008. ©ASCE, ISSN 0733-9437/2008/1-60–66/
$25.00.60 / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING © ASCE /
2000; Svendsen and Murray-Rust 2001�. The World Bank playedan important catalytic role in this acceleration. The impetus forthis change was the combined effect of a national budgetary crisisand rapid growth in the wage costs of unionized labor in the early1990s. The growth of wage costs raised the proportion of expen-diture on operation and maintenance personnel, while reducingthe funds available for materials and equipment. This brought onthe prospect of widespread rehabilitation of large-scale irrigationschemes caused by deferred maintenance, resulting from the un-derfunding of O&M �Svendsen and Murray-Rust 2001�. In 1993,it was estimated that there was an 83% shortfall between O&Mallocations to the DSI and collected tariffs �Vidal et al. 2001�.
It is considered that water prodigality due to excess seepageand operation losses and maintenance-repair expenses are highamong the principal problems that are encountered in open canalirrigation systems, which were transferred to water user associa-tions �WUAs�, �Çevik et al. 2000�.
The performance of an irrigation canal system depends notonly on how the system is operated, but also on the condition ofthe canals. Irrigation canals function well so long as they are keptclean and are not leaking. If no attention is paid to the canalsystem, plants may grow and the problem of siltation may arise.Even worse, the canals may suffer from leakage. A good mainte-nance program can prolong the life of canals. Thus, a routine,thorough program should be kept up. Maintenance of an irrigationcanal system is usually carried out between two irrigation sea-sons, or at times of low water demand. It consists of cleaning,weeding, desilting, reshaping, and executing minor repairs �Vanden Bosch et al. 1992�.
The rate of flow of water in canals is a function of the slope,roughness, and shape of the canal. This relationship is calledManning’s equation. The Manning’s roughness coefficient in bothartificial and natural canals depends on surface roughness, veg-etation, silting and scouring, canal irregularity, canal alignment,
obstruction, size and shape of canal, stage and discharge, seasonalJANUARY/FEBRUARY 2008
change, suspended material, and bed load �Chow 1973�. Canalsare designed to a uniform depth profile corresponding to the de-signed discharge using a Manning’s coefficient appropriate toconditions of good maintenance. When the condition of a canaldeteriorates owing to obstruction, the deposit of sediment and/orgrowth of weeds, its discharge decreases �Cornish and Scutsch1997�. Plant growth and sedimentation not only impede the flowin a canal because of increased roughness, they also diminish thearea of the cross section. As a consequence, the canal capacitymay diminish. Irrigation canals and ditches are often cleaned ofweeds and debris before the irrigation season in order to bettertransport water to farmers during the growing season. From thesestatements, it may be seen that Manning’s roughness coefficientcan be used in the evaluation of a canal’s maintenance condition.
In water distribution in Turkey’s open canal irrigation net-works, the projected canal capacity is usually used in calculations.However, hydraulic characteristics of irrigation canals may differfrom their projected values during and after construction, andprojected and actual canal capacities may not coincide. This mayderive from planning or construction errors, or reconstruction andmaintenance work, and results in two important problems inwater delivery: �1� canals may overflow; �2� the actual canal ca-pacity may be insufficient to convey the water required. Theseproblems show that planning carried out according to actual canalcapacities and not projected values is necessary for efficient man-agement and operation of a water delivery system. In addition, itis of great importance to analyze the hydraulic characteristics ofthe canals of a water delivery network as well as maintenance andrepair work, in order to identify and solve physical problems ad-versely affecting water delivery performance.
Ijir and Burton �1998� developed a numerical indicator, thecarrying capacity ratio �CCR�, for use in evaluating the state ofcanal maintenance. CCR is the actual capacity of the selectedcanal, divided by its designed capacity. In applying this indicator,flow should be measured at the designed water level or head.However, it is not always possible when taking measurements forwater levels at measurement points to be at projected levels. Inthe present work, an indicator of active canal capacity that avoidsthis problem is developed for use as a canal maintenance indica-tor.
Repair and maintenance work at the main, secondary, and ter-tiary levels of the selected canals in the Menemen right and leftbank irrigation networks at the end of the Lower Gediz Basinwere evaluated according to this newly-developed indicator andthe Manning’s roughness coefficient.
Material and Method
Operation and Maintenance Activities on the IrrigationSystem in the Gediz Basin
The irrigation system of the Lower Gediz Basin in the west ofTurkey comprises ten irrigation associations, which serve about96,000 ha. Mainly cotton and grapes are grown in the basin, andthe land is irrigated in the period from May to September whenrainfall is insufficient. Routine repair and maintenance work iscarried out in spring before the start of the irrigation season.
WUAs operate all secondary and tertiary gates, they deviseand develop water distribution policies among farmers, and theyare fully responsible for implementing water allocation. WUAsalso have full responsibility for maintaining the secondary and
tertiary canals. In most systems, the WUAs hire temporary laborJOURNAL OF IRRIGATION AND DR
for canal cleaning, lifting concrete flumes, cutting grass, anddesilting the canals. In addition, small drains internal to theWUAs are the responsibility of the WUAs �Svendsen andMurray-Rust 2001; Svendsen and Nott 1999�.
The DSI continues to operate main canals serving more thanone WUA, river regulators, dams, and other major water controlinfrastructures. It also maintains larger drains. The village irriga-tion committees �VICs�, which are the lowest unit of a WUA,take responsibility for tasks such as collecting and submittingfarmers’ water demand forms, managing water distribution belowthe secondary canal level, and cleaning and carrying out minorrepairs on canals, siphons, and concrete flumes. For this, theyreceive a share of the water charges �DSI 2000�.
All maintenance work on the main and secondary irrigationand drainage canals is financed from the association’s budget,while at the tertiary level, these expenses are met by a payment tothe VICs from the association’s budget. The share of the associa-tion’s budget allocated to the VICs is 25%. However, money al-located from the budgets of many of the associations in the basin,whether for maintenance work or for the VICs, remains belowthis level �DSI Irrigation Associations Bulletin�.
Menemen Irrigation Network
This study was carried out in the Menemen Irrigation Network,which serves 22,865 ha of land of the plain at the end of theLower Gediz Basin. The plain consists mainly of alluvial land.Annual average temperature is 17°C and annual average rain is510 mm. The main crops grown are cotton and grapes, and alsocitrus, cereals, and vegetables are grown �Droogers et al. 2000�.
Water diverted from the Emiralem Regulator on the GedizRiver to the irrigation system of the Menemen plain is distributedthrough the right and the left bank irrigation networks �Fig. 1�.The left main canal network, along with its regulator, wereopened for irrigation in 1944. It was constructed partly of earthand partly of concrete-lined trapezoid canals, but later the wholenetwork was lined with concrete. The right bank network wasopened in 1974. The main canal is a trapezoid section open canal,while the secondary and tertiary canals are all concrete flume. TheMenemen irrigation network has a total of 49,789 m of maincanals, 151,044 m of secondary canals, and 547,599 m of tertiary
Fig. 1. General plan of the Menemen Irrigation Network
canals �DSI 2000�. Water management in the irrigation system is
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carried out by 31 irrigation groups and the Menemen Left andRight Bank WUAs, which were founded in 1995.
In the research area, limited renovation, together with landconsolidation starting in 1990, has been carried out. In this con-nection, an increase in the length of tertiary canals has occurred inthe left bank irrigation network, and deformed trapezoidal con-crete canals have been turned into concrete flumes �Ünal Çalışkanand Ünal 2005�.
This work was carried out on the left and right bank maincanals, on the five secondary canals of Kesikkoy, Seyrekkoy, Ulu-cak, Sasali, and Kaklic, and the tertiary canals dependent on them�except for Kalkic�, of which there are three each, or 12 in all. Onthe selected parts of these canals where measurements weretaken, rehabilitation work has not taken place subsequent to suchconstruction work as renewal of the concrete lining.
Method
Determination of Measurement Points on SelectedIrrigation Canals
Measurement points on the chosen canals were selected accordingto the following criteria: �1� the water level in the canal was closeto maximum; �2� nothing happened to change the water levelswhile measurements were being taken; �3� the cross-section ge-ometry of the canal being measured was not deformed and did notcause any obstruction to flow.
The study was carried out according to these criteria at a totalof 45 measurement points, ten on the main canals �four on the leftbank and six on the right bank�, 16 on the secondary canals, and19 on the tertiary canals.
Determination of Manning’s Roughness Coefficient „n…
Manning’s roughness values were calculated at the designatedmeasurement points on the main, secondary, and tertiary canals ofthe study area using Manning’s velocity equation
n =R2/3 · S1/2
V
where n=Manning’s canal roughness coefficient; R=hydraulic ra-dius �m�; S=slope �mm−1�; and V=velocity �ms−1�.
The value of R was determined as the ratio of the cross-sectionarea to the height of the water �A� and wetted perimeter �P� ateach measurement point. The value of V was stated as the averagevelocity at the measurement points on these canals. In order todetermine average velocities of flow in the canal cross sections,the canal cross section at the measurement points was first di-vided into subsections, and velocity values were measured foreach subsection by the two-points method, using a propeller cur-rent meter calibrated by DSI Hydraulic Laboratory �USBR 2001�,then the weighted average of the measured velocity values foreach subsection were calculated according to the area of eachsubsection. In order to minimize the effect of the control gates onmain and secondary canals, velocity measurements were made atthe time of most intensive irrigation and when water levels in theselected canals were close to maximum. The water level was keptstable during measurement by keeping control of the gates of thecanals, that is, by maintaining the same amount of opening of thecheck gates on main and secondary canals and of the turnout
gates on the tertiary canals. In this way, uniform flow conditions62 / JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING © ASCE /
were provided. This was checked by measuring flow depths whilemeasurements were being taken. The value of S for each canalwas taken from DSI �1995� records.
In order to evaluate the physical condition of the canals in-cluded in the study, values of n obtained were compared withvalues of n in Table 1, which were selected from the publishedliterature of Kraatz �1977�, Acatay �1996�, and Brater et al.�1996�.
Estimation of Active Canal Capacity
Active canal capacities �ACCs� were calculated at the measure-ment points of the selected canals in the study area using thefollowing equation:
ACC =Qactual
Qprojected· 100 =
Vactual
Vprojected· 100 =
nprojected
nactual· 100
where ACC=active canal capacity �%�; Q=actual and projectedcanal capacity �m3 s−1�; V=actual and projected water velocity�ms−1�; and n=actual and projected Manning’s roughness coeffi-cient.
The development of this equation was based on the carryingcapacity ratio �CCR� indicator proposed by Ijir and Burton �1998�for evaluating the maintenance condition of canals. CCR is theactual capacity for the selected canal, divided by its designedcapacity �Qactual /Qprojected�. The ideal ratio would be 1. In applyingthis indicator, flow should be measured at the designated waterlevel or head. However, it is not always possible when takingmeasurements for water levels at measurement points to be atprojected levels. In addition, it is possible to operate a canal toofull, reducing canal freeboard to an unsafe margin. In this study,sections were chosen without plant growth and siltation, andwhere the canal cross section was unchanged. With these condi-tions, the second part of the ACC equation was obtained from thefirst part. Further, assuming that projected canal slope values inthe Manning’s velocity equation were the same as actual values,the third part of the ACC equation was obtained, and solutionswere reached in accordance with the final part.
In the ACC equation, the value nactual indicates values obtainedfrom a previous Manning’s equation. The value nprojected wasbased on the value of n=0.016 observed in irrigation system plan-ning in Turkey �Acatay 1996�. ACC values indicate the extent towhich the projected capacity had been made use of, as a percent-age. ACC�100% shows that projected canal capacity is reduced,while ACC�100% shows that it is increased. In other words,deviation of ACC values from 100% indicate changes to the ca-nal’s projected hydraulic characteristics, i.e., errors in canal con-
Table 1. Canal Conditions with respect to Manning’s Coefficient ofRoughness �n� for Concrete Lined Canals
n Canal condition
0.011 Best �exceptional�
0.014 Good
0.016 Fair
0.019 Bad
struction or inadequacy of repair and maintenance work.
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Results and Discussion
Values of Manning’s roughness coefficient �n�, and active canalcapacity �ACC�, along with values of other hydraulic parameterssuch as flow cross section �A�, wetted perimeter �P�, hydraulicradius �R�, and average velocity �V� used in the calculations, ob-tained at the 45 measurement points, are given in Table 2 for maincanals, Table 3 for secondary canals, and Table 4 for tertiarycanals.
Maintenance at Main Canal Level
Looking at Table 2, it can be seen that flow velocities in maincanals are high, as are flow cross section and hydraulic radiusvalues. The left bank main canal, with a larger flow cross section,had flow velocities of 0.7168 to 1.1016 ms−1, while the right bankmain canal flow velocities were between 0.4924 and 0.6034 ms−1.Values for n for the two canals were close: 0.021–0.028, average
Table 2. Hydraulic Parameters Used in Calculations, Water Height, n, a
Canal nameMeasurement
pointA
�m2�P
�m�
Left main canal 1 17.328 13.13
2 17.513 13.03
3 10.375 10.70
4 15.727 12.95
Main canal average
Right main canal 1 3.659 5.91
2 4.060 5.84
3 3.200 5.18
4 3.050 5.30
5 4.216 6.04
6 4.352 6.08
Main canal average
Overall average
Table 3. Hydraulic Parameters Used in Calculations, Water Height, n, a
Measurementpoint
Canalnamea
A�m2�
P�m�
1 Ke 4.784 6.55
2 Ke 3.531 5.65
3 Ke 3.764 5.65
4 Ke 2.912 4.85
5 Se 6.937 7.58
6 Se 6.247 7.21
7 Se 6.889 7.58
8 Se 6.593 7.64
9 U 6.995 7.78
10 U 7.620 8.74
11 Sa 3.819 5.72
12 Sa 2.994 5.23
13 Sa 1.806 4.07
14 Sa 1.654 3.94
15 Ka 1.123 3.23
16 Ka 1.030 3.14
Averagea
Ke=Kesikkoy secondary; Se=Seyrekkoy secondary; U=Ulucak secondary; SaJOURNAL OF IRRIGATION AND DR
0.023, for the left main canal and 0.021–0.026, average 0.024, forthe right main canal. The ACC value for the left main canal wascalculated as 57–80%, with an average of 72%. The value for theright main canal was 62–76%, with an average of 67%.
Values of n for both main canals, when compared with Table1, rate “Bad” �n�0.019�. This also has an adverse effect on thecanals’ active canal capacity �ACC�100% �. In this way, pro-jected water transmission capacities are reduced by an average of31% �ACC=69%, Table 2�.
The fact that values of n and ACC for main canals are poorshows that the physical condition of the canals is bad, and thatmaintenance is insufficient. It can be said that among the mostbasic reasons for the increase in roughness and, thus, the decreasein active canal capacity, are degradation of the concrete used inthe canal lining, breakup of the linings, algae, and sedimentation.These problems, especially the degradation and breakup of thecanal linings, were determined by field observations.
C at Main Canal Level
R�m�
V�ms−1�
Waterheight �m� n
ACC�%�
1.319 1.0110 1.92 0.021 76
1.344 0.9885 1.98 0.021 76
0.969 1.1016 1.25 0.020 80
1.214 0.7168 1.80 0.028 57
0.023 72
0.619 0.6034 1.12 0.021 76
0.695 0.5417 1.16 0.025 64
0.618 0.4924 1.00 0.026 62
0.575 0.5054 1.00 0.024 67
0.698 0.6021 1.24 0.023 70
0.716 0.5636 1.28 0.025 64
0.024 67
0.023 69
C at Secondary Canal Level
V�ms−1�
Waterheight �m� n
ACC�%�
0.5219 1.30 0.022 73
0.6583 1.10 0.016 100
0.5763 1.18 0.019 84
0.6924 1.12 0.015 107
0.7355 1.64 0.018 89
0.8051 1.55 0.016 100
0.7350 1.65 0.018 89
0.7600 1.54 0.017 94
0.8331 1.34 0.019 84
0.7546 1.27 0.021 76
0.5866 1.12 0.018 89
0.6395 0.94 0.015 107
0.5340 0.70 0.015 107
0.5291 0.63 0.015 107
0.3887 0.58 0.018 89
0.3793 0.50 0.018 89
0.018 93
nd AC
nd AC
R�m�
0.730
0.625
0.666
0.600
0.915
0.866
0.909
0.863
0.899
0.872
0.668
0.572
0.444
0.420
0.348
0.328
=Sasali secondary; and Ka=Kaklic secondary.
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Maintenance at Secondary Level
Looking at Table 3, it can be seen that flow velocities in canalsare high, as are flow section and hydraulic radius values, espe-cially in Seyrekkoy and Ulucak secondaries, which are biggerthan the others. Flow velocities in secondary canals were found tolie between 0.3793 and 0.8331 ms−1. Taking all secondaries to-gether, values of n were between 0.015 and 0.022 with an averageof 0.018. ACC values were between 76 and 100% in the Sey-rekkoy, Ulucak, and Kaklic secondaries, and between 73% and107% in the Kesikkoy and Sasali secondaries, with an average of93%.
When compared with n values in Table 1, parts of Sasali andKesikkoy rate Good-Fair, Seyrekkoy and Kaklic secondaries rateFair-Bad, while Ulucak secondary and the other part of Kesikkoyrate Bad. The overall rating for secondaries was Fair-Bad. ACCvalues showed that secondary canals generally were able to de-liver water at close to projected capacity �ACC�100% �. More-over, in some parts of Kesikkoy and Sasali secondaries �withACC�100%�, it was found that because canal bed slope wasgreater than the projected value, whether from settling of thecanal bed or from errors at the time of construction, water deliv-ery capacity was somewhat higher than projected. These values ofn and ACC show that overall, rather more attention needs to bepaid to secondary canal repair and maintenance work.
Maintenance at Tertiary Level
Looking at Table 4, it can be seen that in the 19 selected tertiaries,measured flow cross sections varied from 0.171 to 0.730 m2, andvelocity values were between 0.1546 and 0.4710 ms−1. Overall,values of n in tertiaries were between 0.011 and 0.039, with anaverage of 0.023. ACC values were 55–145% in Ulucak andSasali tertiaries, 44–107% in Seyrekkoy tertiaries, and 41–70% inKesikkoy tertiaries, with an average of 81%.
Table 4. Hydraulic Parameters Used in Calculations, Water Height, n, a
Measurementpoint Canal namea
A�m2�
P�m�
1 Ke-2 0.730 2.42
2 Ke-23/1 0.528 2.10
3 Ke-23/1 0.525 1.99
4 Ke-16 0.537 2.38
5 Se-1 0.418 1.87
6 Se-1 0.720 2.40
7 Se-31 0.564 2.07
8 Se-31 0.666 2.21
9 Se-36/1 0.450 1.90
10 Se-36/1 0.577 2.18
11 U-12 0.209 1.38
12 U-12 0.171 1.20
13 U-20 0.347 1.66
14 U-20 0.729 2.45
15 U-24 0.347 1.70
16 U-24 0.638 2.38
17 Sa-2 0.591 2.07
18 Sa-13 0.243 1.54
19 Sa-17 0.520 2.04
AverageaKe=Kesikkoy tertiary; Se=Seyrekkoy tertiary; U=Ulucak tertiary; and
Compared with values of n in Table 1, tertiaries generally rate
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Bad. Nevertheless, in five tertiaries where measurements weremade �at measurement points 5, 12, 13, 15, and 18�, values of ncan be seen to be below the projected value �n�0.016�, and thattwo of these �measurement points 13 and 15� have n values sug-gesting a very good maintenance condition for the canal �n=0.011�. However, it was shown from field observations thatcanal bed slope was greater than the projected value, either fromcanal bed settling or because too great a slope had been givenduring construction, resulting in increased flow velocity. ACCvalues for most tertiaries �11 canals� showed delivery capacitiesto be well below projected values �ACC�100% �, and weremuch above them in only five tertiaries �ACC�100% �.
All these results indicate that roughness has caused a reductionon canal capacities compared with those foreseen at the planningstage. In addition, the fact that roughness values vary, shows thatthe physical and maintenance condition of the canals is very vari-able. At the time of measurement, it was observed that the physi-cal and maintenance condition of some canals was good, whilefor others it was very bad. The prime reason for this variability isthat canal maintenance is carried out by various different irriga-tion groups. It can, thus, be seen that some irrigation groups donot pay enough attention to repair and maintenance.
Overall State of Maintenance Work at Irrigation SystemLevel
Results obtained from the study show that the general state ofmaintenance of the system is not good regarding roughness andwater delivery capacity. It was determined that roughness, whichis caused by such factors as increasing silting, plant growth, anddamage to concrete linings, was greater in main and tertiary ca-nals than in secondaries, while water delivery capacities of sec-ondary and tertiary canals were better than those of the maincanals. In particular, increased canal slope in tertiary canals, re-
C at Tertiary Canal Level
�V
�ms−1�Water
Height �m� nACC�%�
02 0.1618 0.50 0.039 41
51 0.2467 0.48 0.023 70
64 0.2388 0.50 0.024 67
25 0.1546 0.37 0.034 47
24 0.3375 0.44 0.015 107
00 0.1884 0.60 0.034 47
72 0.3640 0.48 0.016 100
01 0.2397 0.60 0.027 59
37 0.2765 0.51 0.020 80
65 0.1632 0.52 0.036 44
51 0.2110 0.24 0.019 84
43 0.2583 0.22 0.015 107
09 0.4710 0.34 0.011 145
97 0.2146 0.54 0.029 55
04 0.4573 0.35 0.011 145
68 0.2444 0.50 0.024 67
86 0.3026 0.55 0.020 80
58 0.3527 0.27 0.012 133
55 0.2122 0.52 0.027 59
0.023 81
sali tertiary.
nd AC
R�m
0.3
0.2
0.2
0.2
0.2
0.3
0.2
0.3
0.2
0.2
0.1
0.1
0.2
0.2
0.2
0.2
0.2
0.1
0.2
Sa=Sa
sulting from canal bed settling or from construction errors, meant
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that calculated roughness values were low, and as a result, canalcapacities were high. In the system as a whole, factors resultingfrom poor maintenance such as plant growth, cracking, and de-formation, along with algal growth, have together resulted in anumber of problems.
Vegetation growth in canals increases evapotranspirationlosses. It has been generally agreed that vegetation increases flowresistance, changes backwater profiles, and modifies sedimenttransport and deposition �Yen 2002�. Roots and decomposingplant material produce organic acids, which react with the cal-cium in the concrete of the canals, causing corrosion �Letsoaloand Van Averbeke 2006�. In addition, vegetation growth reduceswater flow velocity and increases irrigation time.
Cracks and damage to canals increase canal seepage losses.Akkuzu et al. �2005�, in a study that determined seepage losses inthe canals of the same system, found seepage losses of 0.0141,0.0615, and 0.0598 ls−1 m−2 for main, secondary, and tertiary ca-nals, respectively. Kraatz �1977� has stated that if the concretecanals were built in a suitable way and well maintained, seepagelosses would occur below the value of 0.03 m3 m−2 day−1 �about0.0003 ls−1 m−2�. When evaluated in this light, it can be seen thatcanal repair and maintenance work on the canals is insufficient.Moreover, freeboard is used to enable the canals to take morewater, giving rise to overflow, and, thus, danger and wastage ofwater.
Because an increase in roughness reduces the canal’s capaci-ties, it gives rise to operating problems with regard to sufficiencyand flexibility. The fact that an important part of the irrigationarea’s crop pattern is cotton means that irrigation is concentratedin certain specific periods. At these times, reduction of canal ca-pacity due to roughness increases problems of insufficiency incanal capacity. Ünal et al. �2004�, in a study that obtained theopinion of farmers on the realization of water delivery in the sameirrigation system, found that a significant proportion of farmersstated that water delivered to canals was insufficient, and com-plained of such problems as breakage, cracking, subsidence, silt-ation, and the buildup of weed. Kiymaz et al. �2006�, in a studycovering the irrigation associations of the Gediz Basin, examinedtechnical, economical, training, and social problems by means ofa questionnaire to water users. In this study too, water users com-plained of deteriorated infrastructure, leakage, weed growth, andsedimentation.
Another factor that increases roughness is algae in the irriga-tion water. Chow �1973� stated that suspended material, whethermoving or not moving, would consume energy and cause headloss or increase the apparent canal roughness. At certain times inthe irrigation season, water velocities in canals are significantlyreduced because of algae, and water cannot be supplied in therequired amounts. Thus, associations occasionally add copper sul-fate to the irrigation water in order to prevent algal growth. Whenalgal growth is excessive, the associations cut off the water sup-ply, and allow the canal to dry out for a few days. This paralyzesirrigation operations.
The fact that maintenance and renovation work is not or can-not be carried out sufficiently, or is neglected, as well as givingrise to these water loss and operation problems, also threatens thecontinued running of the irrigation system. However, solvingthese problems with current budgets is exceedingly difficult. Themoney that the WUAs spend on maintenance and repair has asmall share in their budget. For instance, the expenditures of theMenemen Left Bank Water User Association between the years1998–2002 for maintenance-repair work constituted 2.5–13.7%
−1
of its budget �between $13,000– $64,000 year � �Assik et al.JOURNAL OF IRRIGATION AND DR
2004�. Kiymaz et al. �2006� also determined that system renova-tion work was needed. They also stated that most associations didnot have the requisite machinery to carry out maintenance workon time, that irrigation association managers were unable to allotfunds for maintenance work because of financial constraints, thatpayments for irrigation water collected from users was insuffi-cient for the maintenance and upkeep of the system, and that thefarmers’ contribution was insufficient.
Conclusions
In this study, conducted on the Menemen Irrigation System in theLower Gediz Basin, roughness of canals, and their state of main-tenance in relation to this, was examined. Manning’s roughnessvalues of 0.023 were found for main and tertiary canals, and0.018 for secondary canals. Subsidence, lining deterioration, silt-ation, and weed and algal growth all served to increase thisroughness. The fact that actual roughness was higher than pro-jected values meant that canal capacities were reduced. The studyfound that this reduction averaged 31% �ACC=69% � for maincanals, 7% �ACC=93% � for secondary canals, and 19% �ACC=81% � for tertiary canals.
These results have shown that, for the success of hydraulicmodels and water delivery programes for irrigation systems,roughness and canal capacity parameters must be based on actual,rather than projected values. However, well water delivery pro-grames are drawn up, if it is not possible to use actual canalcapacities in the calculations, and good operational performancecannot be expected. The same applies with regard to successfulhydraulic modeling.
As stated above, it is possible to perform repair and mainte-nance work sufficiently, and as is required for the continued run-ning of the irrigation system. Therefore, it is necessary to findways of increasing funds allotted for repair, maintenance, andrenovation, and to research types of lining that are suitable for theregion and more economical. Moreover, it is necessary to enableusers to play a more active role in the repair, maintenance, andpreservation of the canal.
Notation
The following symbols are used in this paper:ACC � active canal capacity �%�;
n � Manning’s canal roughness coefficient;nactual � actual Manning’s roughness coefficient;
nprojected � projected Manning’s roughness coefficient;Qactual � actual canal capacity �m3 s−1�;
Qprojected � projected canal capacity �m3 s−1�;R � hydraulic radius �m�;S � slope �mm−1�;V � velocity �ms−1�;
Vactual � actual water velocity �ms−1�; andVprojected � projected water velocity �ms−1�.
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