6.1 Main functions
6.2 Types of maintenance
6.3 Maintenance activities
6.4 Planning maintenance activities
6.5 Implementation of the maintenance programme
6.6 Staffing the maintenance service
6.7 Organizational structure
The irrigation network is perhaps the most costly element of an irrigation scheme and is designed to last a long time. However, all too often one finds that irrigation schemes not long constructed bear little resemblance to the original construction and design. Silt deposition, weed infestation, malfunctioning of structures and other undesirable situations make it practically impossible to control the flow in these canals. As a result, the system is unable to deliver the necessary water and distribute it equitably. It is not surprising that farmers working in those irrigation schemes sometimes feel frustrated because they know the potential benefits of irrigation and yet cannot realize their expectations.
On the other hand, there are many examples illustrating that with proper maintenance and cooperation among farmers in this task, irrigation systems may last much longer than their original designers or constructors ever envisaged. Irrigation schemes that have been in operation for centuries can be found in Spain, Egypt, Italy, Pakistan and other countries, and are a living testimony that properly maintained irrigation schemes can be of permanent benefit to many generations.
There are several reasons for poor maintenance: just to mention the most important:
- insufficient funds made available to the management;
- lack of interest by the farmers in participating or collaborating in the maintenance work;
- poor organization of the work.
The most widespread cause for poor maintenance in public irrigation schemes is the lack of sufficient funds for servicing and repair. As this not only affects the maintenance but the whole water management organization, it will be dealt with separately under the Administrative Service (Chapter 8).
Lack of interest by the farmers in participating in maintenance work is sometimes the chief reason for a state of disrepair of the tertiary canals or watercourses for which the farmer may have been made responsible. The reason for this lack of interest, demonstrated by the farmer disassociating himself from repair and maintenance work, can have various causes and be complex. In some cases, the farmer does not realize the importance of maintenance work nor does he know how to do it, or be feels that his work benefits others rather than himself. In yet other situations, the farmer does not identify the irrigation system as his own system and therefore purposely avoids any participation in the maintenance work. To improve such situations, each case should be analysed to discover the reasons for non-participation and the assistance of sociologists can be helpful in determining them.
Poor maintenance may also result from inadequate planning of such work, or it may be that the available resources have not been used to the best advantage.
This chapter provides some guidelines for the planning and undertaking of the maintenance work. It is assumed, for reasons of simplicity, that the project management is responsible for the maintenance of main and secondary canals.
One interesting observation regarding the need for maintenance is that it is greater in "low-cost technology" constructed irrigation schemes than in "high-cost technology". To illustrate the point: a concrete lined canal requires less maintenance than an earth canal. Since most of the developing countries tend to use low-cost technologies, because of limited funds, the consequence is that maintenance requirements should receive greater attention. Unfortunately, it is precisely in these countries that maintenance receives less attention, the causes being several, such as: poor administrative organization, shortage of funds, etc. The point to be made here is not that high-cost technologies should be used because less maintenance is required but that, when using low-cost technologies, special attention should be paid to the maintenance problem if the scheme is to work properly. Where there is little hope that maintenance will be satisfactory, the choice of a high-cost technology design may be justified, but keeping in mind that, although the maintenance requirements of such schemes are smaller in terms of manpower, they require highly specialized personnel.
Another reason for differences in maintenance requirements is the degree of completion of the irrigation system. All too often, an incompleted irrigation scheme is handed over to the ministry (usually of agriculture) responsible for its 'operation and maintenance'. Obviously the difficulties of maintaining and operating such a system are much greater than those for a properly completed one. It should not and cannot be expected that a normal maintenance service will suffice for an incomplete system. Where this is the case, special units must be established to undertake this 'completion work'.
In India, where the completion of many schemes has been considered a matter of urgency, many of the recently established project authorities have special units to complete on-farm developments, i.e. to provide watercourses for water delivery to each farm and to ensure land grading which was not initially undertaken. Special completion or rehabilitation programmes may also be considered in these cases.
The Maintenance Service is entrusted with the overall responsibility for keeping the irrigation and drainage systems working in a satisfactory manner, within the limitations imposed by the initial design.
Similarly to the Operation Service, the main functions to be undertaken are:
- planning the maintenance activities;
- implementing the maintenance activities planned and those unforeseen;
- monitoring the above mentioned activities.
Planning the activities to be undertaken in the following year is particularly important in countries where government allocations for operation and maintenance are made on the basis of planned expenditure. A good justification of the work to be done and the consequences if it is not undertaken is of foremost importance to obtain financing for maintenance work. Even where this is not the case, planning the activities that can be executed within the limited resources available is a useful exercise.
Maintenance activities can be more easily undertaken in the off-season, as during this period, labour from the farming community is normally plentiful. Furthermore, if farmers are engaged in maintenance work on their own land for their own benefit, they' are more likely to work willingly. Also, operational personnel are more free at that time of the year and can be engaged to supervise or execute part of the maintenance work themselves.
A Maintenance Service requires data for good planning which can be obtained by regular monitoring. Without reliable data on costs for the different units of work and on productivity no realistic planning can be done. Later in this text, productivity data are given for machinery and manpower engaged in maintenance operations. They will be helpful when planning and costing activities if no better data are available, but a project should endeavour to have its own data based on the specific conditions of the area.
There are three main types of maintenance, namely:
- routine or normal maintenance which includes all work necessary to keep the irrigation system functioning satisfactorily and is normally done annually;- special maintenance including repairs of damage caused by major disasters, such as floods, earthquakes and typhoons. The unforeseeable nature of such natural phenomena make it very difficult to take specific preventive action, although general safeguards can be installed in particularly prone areas, e.g. large drainage dykes in flood areas. In irrigation schemes located in places subject to these hazards, a "special reserve fund" or budget allocation should be established for repair work;
- deferred maintenance including any work necessary to regain the lost flow capacity in canals, reservoirs and structures when compared to the original design. It often includes large modifications to the canal system and structures arising from important changes (cropping patterns, drainage problems, etc.) that have occurred in an irrigation scheme. In practice, its difficult to differentiate between so-called 'deferred maintenance' and a 'rehabilitation programme'. The difference is mainly of a financial nature, because 'deferred maintenance' is normally undertaken with funds from the national budget allocated to operation and maintenance while rehabilitation programmes are considered as an investment and the funds come from a different source (loans, national development banks, etc.).
This chapter is mostly concerned with routine maintenance, and to some extent with deferred maintenance.
6.3.1 Dam and reservoir
6.3.2 Irrigation network
6.3.3 Drainage network
6.3.4 Rural road network and flood protection dykes
6.3.5 Pump stations
6.3.6 Ancillary works
The maintenance activities for which the Maintenance Service is responsible should be clearly spelled out in the by-laws of the irrigation scheme. While some activities are clearly a responsibility of the Service (silt removal in canals, weed clearing, etc.), there are others not so precisely defined, for instance, rural roads, ancillary works, buildings, the cleaning of the drainage system. Nevertheless, it has 'been decided to include in the text all potential activities that could be the object of maintenance with a brief description of their characteristics and relative importance.
The maintenance activities have been grouped according to the major elements of an irrigation system; they are: (i) dam and reservoir; (ii) irrigation network; (iii) drainage network; (iv) rural road network and flood protection dykes; (v) pump stations; and (vi) ancillary works. They are described below.
Maintenance activities in a reservoir itself comprise:
- controlling aquatic weeds,- removing large debris (e.g. tree trunks) floating in the water that may damage hydraulic works,
- monitoring the water quality: not only from the salt content point of view but also from a biological standpoint in order to detect possible sources of pollution,
- surveying the solid deposition in the bottom of a reservoir.
These activities require little time because they are periodic with the exception of aquatic weed control, which is in any case only likely to be a severe problem in tropical and semi-tropical climates. However, they are extremely important in order to detect promptly the need for corrective action.
The most common water weed in reservoirs in semi-tropical and tropical areas is the water hyacinth (Eichhornia crassipes). This plant represents a serious problem because it forms an ideal environment for mosquito larvae and has an evaporation several (2.2 to 13.4) times greater than an open surface of water. The plant has a very fast rate of growth: two plants can produce enough offspring to cover one acre in less than eight months.
Another frequent problem is eutrophication (over-abundance of nutrients in the water bodies) resulting in high production of blue-green algae and the associated phenomenon of lack of dissolved oxygen in the water. This problem, which is very serious if the water is used for urban water supplies, is less important when the water is used for irrigation, the main consequence of the latter being an increase of vegetation in the irrigation canals and greater weed infestation. Injecting compressed air into reservoir water has proved to be a satisfactory solution on several occasions but there are other techniques that can be applied.
The main maintenance actitivies for an irrigation dam are: lubrication of gates, anti-corrosion treatment, cleaning of debris, control of filters, and some other minor work. Earth dams require greater maintenance, especially the upstream slope where weed control is necessary once or twice a year. The electro-mechanical system of a dam must also receive proper maintenance, particularly electric engines, head gates, and the lighting system. The maintenance of these elements is rather specialized and the manufacturers of the equipment usually provide detailed instructions.
The canals in irrigation networks are generally either of earth or concrete-lined and their maintenance characteristics are quite different.
i. Concrete - lined canals
Concrete-lined canals should require little maintenance, provided that they have been properly constructed and any potential problems studied (subpressure, gypsum soils, swelling clays, etc.) and adequate technical solutions provided. One of the main reasons for constructing concrete-lined canals is precisely to reduce maintenance operations.
The routine activities include: replacement of joints, replacement of damaged concrete slabs, weed control in joints and on the surface of concrete slabs, control and treatment of filters, control and removal of silt. In the case of concrete flumes, chemical sterilization is also needed around the supporting structures.
Under normal conditions, the silting in concrete-lined canals is not an important problem since water velocity is high and sand traps and silting basins are often provided to reduce the solid content of the water. Heavy rain may cause deposition of solid materials if the berms are not properly formed. Drifting sand may be a serious problem in schemes surrounded by desert or bare land and subjected to strong winds. The most effective way of preventing this type of silting is to install windbreaks or barriers where sand accumulates before reaching the canal.
Removal of silt from concrete-lined canals is an expensive operation because it is mainly manual. Mechanical equipment can be used when specially adapted to avoid damaging the lining. In some irrigation schemes, the technique of flushing "quick water" through the canal is used to remove silt from one place and concentrate it in another where it can be more easily removed or disposed of. For this purpose, the canal should be run at its maximum capacity to reach the highest possible velocity.
Weed control should not be a major problem in lined canals, although aquatic weeds must be periodically removed. Later in the text, guidelines are given for weed control in both lined and earth canals.
The main problem in concrete - lined canals is cracking of the lining and eventual eruption of concrete slabs due to subpressure. Apart from repairing the damaged lining, corrective action must be taken. Usually the installation of subpressure valves is enough to relieve the pressure, but this involves major work. An alternative measure can be the construction of a subsurface drainage system to lower the water level.
ii. Earth canals
There are four main problems in earth canals requiring maintenance attention and, although they are closely interrelated, they will be treated separately.
a. Silting
Excessive sedimentation is perhaps the most common problem affecting the performance of earth canals. Malik (1978) identifies the following causes for canal siltation:
1. excessive silt entry at the main canal intake
2. disproportionate withdrawal by branches
3. prolonged heading up at control points
4. drifting sand
5. inadequate transport capacity of channels
6. re-entry of excavated material by rain and wind action
7. malfunctioning of intakes
8. haphazard sediment excavation
9. excessive weed growth
10. wrong channel regulation.
Causes 1 to 5 indicate defective design, 6 to 9 inefficient maintenance, while 10 denotes improper channel operation. Corrective measures for defective design are difficult to implement since they require major physical changes which imply heavy investments. However, the effects of defective design can be reduced by proper maintenance. For example, an erroneous angle between the parent branch and canal may induce the formation of a sand shoal which, if allowed to develop, will accelerate the silting process, thus compounding the consequences. Incorrect operation is also a major cause of silting. Canals carrying a heavy load of material in suspension should not be allowed to run at less than three quarters of their capacity since at lower capacities the velocity decreases inducing silting.
Abrupt shutting of gates, causing rapid changes in flow velocity, may induce bank erosion near the gates.
b. Weed infestation
Weed infestation can seriously impede the flow of canal water not only in tropical conditions but also in semi-arid and arid climates. There are two groups of weeds:
- earth weeds: they root in the soil and their habitat is not the water; they proliferate on the canal slopes and in the banks, benefitting from favourable soil moisture conditions;- aquatic weeds: they can either root in the water or the earth but their habitat is in the water. Robson (1976) classifies them as follows:
· emergent plants - these are plants growing in the water and whose foliage emerges above the surface, e.g. the common read (Phragmites communis);· floating leaved plants - there are two sub-groups with floating leaves: in one, the plants are rooted in the mud and their leaves float flat on the surface, in the other, plants are not rooted but free-floating on the surface;
· submerged plants - this group consists of plants whose foliage is totally submerged; a number of them produce flowers which emerge above the surface; one or two plants are free-floating, but most are rooted in the mud;
· algae - this group consists of a variety of algae of various forms, including unicellular algae and the large filamentous forms.
The relevance of the type of weed to the method of control will become apparent when control measures are discussed. Some of these weeds, such as nutgrass (Cyperus rotundus), are not only a problem in the operation of the canals but can become a menace for the farmers when water transports them into fields. There they reproduce rapidly and become a serious problem because of the difficulty of eradicating them.
Another hazard of weed infestation is the shelter and good breeding conditions they offer for vectors (mosquitoes, snails, etc.) of debilitating diseases.
c. Water infiltration
Water leaks through canal banks can be caused by burrowing small crabs and water rats or by rotting plants and roots which were not removed from the canal bank seat during construction. Ants are also known to be a problem even in concrete-lined canals. These leaks can be repaired by following the path of the leak through the bank either by hand digging or hydraulic backhoe if available and once the path has been found, the trench must be carefully backfilled and compacted. Canal leaks, if not repaired in time, can result in major breaches in banks causing far greater inconvenience and most costly repairs.
Water seepage through porous soils may also be a major concern. Seepage through banks can be considerably reduced by trenching them and burying a plastic membrane or thick slurry made from the excavated material. The trench is backfilled with sand after the barrier has been interred.
d. Erosion of banks
Canal banks can be eroded by heavy rainfall or wind, improper canal operation, stock grazing or passage by drinking animals, and the transit of vehicles. Heavy rainfall or wind can cause serious damage to unprotected banks. Seeding of grasses in the unwetted part of the canal is a cheap and effective protective measure. Short growing varieties (e.g. Agropyron riparium (streambank wheat-grass), Psathyrostachys juncea (Russian wildrye), Festuca ovina (sheep fescue) and Phleum bertolonii (dwarf timothy)) give good results.
Abrupt and rapid shutting off of canal water may also contribute to erosion of the banks. The practice of leaving a canal empty during the rainy season will contribute considerably to erosion of canal slopes.
Cattle and sheep damage the channel banks in different ways (Swales 1976). Cattle tend to push the moist bank material at the waterline into the waterway when they drink. Sheep, however, graze the banks bare thereby allowing wind and rain to wash away the bank material.
Erosion of canals can be repaired by mechanical means or manually by re-building the worn canal banks. However, care should be taken to construct a proper join between the old and the new part, otherwise the canal will deteriorate at the same place.
The most effective measures are of a preventive nature: such as seeding grass mentioned earlier, fencing the canals, and constructing special places for animal watering and bathing.
The retention in good working order of open drains includes the following operations:
- light deforestation
- weed control in the canal section
- seeding grass in the canal section
- maintenance of flow gauges and other measuring devices
- removal of silt
- maintenance of pumping stations where water cannot be evacuated by gravity.
For practical purposes, the maintenance of open drains is very similar to that of earth irrigation canals. However, all too often drainage networks receive much less attention than the irrigation ones. The result is that during heavy rain, when they are much needed, they do not work as they should.
Drainage maintenance should always be programmed from downstream to upstream, and as far as possible completed within an irrigation season. The intervals in regular maintenance should not exceed periods of 2-3 years between two consecutive cleanings.
Tile drains are subject to two main problems: (a) obstruction due to silting and plant roots, and (b) mineral deposits. The most common is the first. Mineral deposits of iron and manganese occur quite frequently in some irrigation schemes and the time necessary for such depositions varies widely from a few months to 30-40 years, depending on the mineral composition of the soil.
Methods for cleaning the drains are discussed later in this publication.
Rural roads are of vital importance in irrigation schemes, especially at harvest time. Many post-harvest losses can be avoided and better marketing facilities obtained by having a fully serviceable rural road network. Whether such networks should be maintained by the Project Management or by the local administrative divisions (village, district) is an internal matter than changes from country to country, and the appropriateness of one or the other position will not be discussed here. For comprehensiveness, it is assumed that such maintenance is the responsibility of the Project Management but let it be understood that this is not always the case. The same consideration applies to flood protection dykes constructed along river banks.
i. Types of roads and their upkeep
Maintenance requirements are different for each type of rural road; these are:
a. all-weather roads (paved)- surfaced with bituminous macadam
- water-bound macadamb. dust-roads or access tracks
c. berms of canal banks and dykes.
All-weather roads are mostly damaged during the rainy season combined with the action of traffic. Repairs imply removal of loose material, refilling of holes with the base and sub-base material, compaction of the layers and resurfacing. Most of these operations are normally manual except for the compacting which is done with heavy rollers pulled by tractors and the hauling of crushed material by trucks or trailer/tractor units depending on the haulage distance.
Macadam roads are more susceptible to damage than bituminous surfaced roads, but they are also easier to repair with the machinery normally available to maintenance units (scrapers, motor-scrapers). Dust roads deteriorate rapidly in rainy conditions and become unusable without proper maintenance. Unfenced roads can also be damaged by stock using the tracks. Repairs and maintenance can be greatly reduced by keeping the shoulder drains in good condition to evacuate excess water quickly. These tracks are usually graded by mechanical means for long stretches, whereas a small tractor-mounted blade is used for small sections. Grading can only be done when soil moisture conditions are suitable. This entails either waiting long periods before the machinery can be brought to the damaged places or in the other extreme, wetting the surface.
Maintenance of the berms of canal banks or flood protection dykes is similar to that for dust roads. Preventive measures, such as prohibition of traffic on banks and berms which are not supposed to be used by heavy machinery (trucks, tractors, etc.) may considerably reduce the maintenance needs. Flood protection dykes can be badly damaged in severe flood conditions and as such situations cannot be anticipated, their repair must be by so-called special maintenance, for which special budget allocations are needed.
Pumping stations for irrigation schemes may be:
a. main irrigation lift-pump stations (surface water or groundwater);
b. booster-pump stations for additional lifts in the main or branch canals;
c. drainage-pump stations.
The first two are usually of medium to high lift, required to pump forecasted quantities of water for long continuous periods. The last is usually for low lift with much larger quantities of water and required to operate intermittently. The irrigation pumps are usually manually controlled whereas the drainage station is frequently float controlled to ensure automatic starting once drainage levels in the scheme begin to rise above a pre-set level. A manual operator should also be on call even with an automatic control.
Operation and maintenance tasks for electric pump stations are comparatively simple, those for diesel operated a little more complex. The operators must be given clear instructions on safety measures, on the methods of starting the pump motors and the way in which they must be brought into full operation. Electric motors sometimes require to be stepped up in speed manually at a strictly controlled rate. Also canals may be damaged if all pumps come rapidly into full operation.
They must also be given a programme of irrigation quantities to be pumped i.e. 1, 2 or 3 etc. pumps to be operating. Where 24 hour pumping is not provided, account must be taken of the rate of rise and fall of canal levels in the irrigated area. It is of little use with a 12 hour pumping schedule if canals do not fill up until late in the morning and still remain full long after dark.
In case of an emergency, there must be some system for easy communication between the pump house operator and the officer in charge - either telephone or signal or runner.
The hydraulic structures in an irrigation scheme include: gates, inlets, spillways, outlets, dividers, siphons, jumps, check dams and other minor structures. Maintenance of such items, when they are constructed in concrete, is restricted to the removal of silt and obstructions. The mechanical elements require periodic greasing. Iron elements require antirust treatment. The same applies to structures in drainage networks (culverts, drainage outlets) and those in road networks (bridges, culverts, crossings, etc.).
Administrative buildings and some other special installations (stores, workshops) require a certain amount of upkeep and should not be overlooked.
6.4.1 Inventory of the works
6.4.2 Volume of maintenance activities
6.4.3 Optimum cycle of maintenance
6.4.4 Machinery and manpower requirements
6.4.5 Costing and establishing maintenance priorities
In order to be able to formulate a maintenance programme, the following steps must be taken:
i. make an inventory of all the works that require maintenance;
ii. determine the volume of maintenance activities to be undertaken annually;
iii. establish the optimum cycle of maintenance for each type of work;
iv. determine the machinery and manpower requirements to undertake the maintenance;
v. budgeting and establishing the maintenance priorities.
Most irrigation schemes already have maps available, also lists of the main works and structures, but for maintenance purposes it is necessary to group the latter into types with similar characteristics. In this way, calculations can be simplified and machinery utilized to the optimum. The grouping is a peculiarity of each irrigation scheme. As an example, the "Secretaría de Agricultura y Recursos Hidráulicos" of Mexico (SARH) classifies an earth canal for maintenance purposes as follows:
|
Canal Type |
Width of Base |
Height of Water |
|
(m) |
(m) |
|
|
A |
10 - 20 |
> 3 |
|
B |
8 - 10 |
2.5 -3.0 |
|
C |
4 - 6 |
1.8 -2.4 |
|
D |
2 - 4 |
1.3 -1.7 |
|
E |
1 - 2 |
< 1 -1.2 |
Other works (roads, structures, lined canals, etc.) can be grouped similarly.
In order to prepare a maintenance programme, the amount of work to be undertaker under each category of maintenance must be known. Many of these activities are mentioned in 6.3 of this Chapter. A detailed list of maintenance works should be prepared for the main elements in the irrigation canal network, the drainage system, and for work concerning roads, buildings and workshops.
The extent of work to be undertaken is in most cases determined by visual inspection, followed by detailed measurement of the volume, area, or unit lengths of each task. The most complex estimate is generally that of silt clearance, since owing to variations in the sections of the canal and consequent differences in water velocity, the silt is deposited unevenly. The amount of silt deposition in the different stretches of a given canal may quite well differ 3-5 times.
In order to determine the amount of silt to be removed, a topographical survey is made by taking the sections every 50 or 100 m according to the required degree of precision. With the data obtained the area of the sections is calculated. The volume of sediment (Vp) for each stretch of length &, will be:
Vp = ½(A1 + A2) l
where A and A are the transversal section of the sediment and l the length of the section, and therefore for a canal of constant section:
Vp = {½(A1 + An) +A2 + A3 + .....An-1} l
Once all the measurements of the maintenance are complete, they should be grouped according to activity in order to study the manpower and machinery requirements.
The optimum cycle of maintenance is the time that can safely elapse between two consecutive maintenance operations of a constructed element (canal, road, drain, etc.) without that element failing and disrupting the efficient operation of the whole. A certain degree of malfunctioning (10-20 percent reduction in absolute efficiency with respect to the design) is normally acceptable between the two consecutive maintenance operations. For instance, in a given canal, a reduction of the flow by 15 percent in relation to the design capacity-may be acceptable during the silt removal cycle of three years. If the reduction in flow is greater, water distribution will be adversely affected and the cycle will have to be shortened to one or two years.
Therefore, for each servicing activity the optimum maintenance cycle must be known. As it is determined by local factors such as climate, length of irrigation season, quality of the water, quality of the construction, etc., it should be based on experience gained in the particular project. During the initial years, when such experience does not exist, it is usually advisable to rely on experience gained by other irrigation schemes with similar conditions in the country. As a general indication, the cycles of maintenance used by SARH are given in Table 2.
The next step in the maintenance programme is to determine the machinery and/or manpower required to undertake the amount of work already identified. Several methods can be used for the maintenance work, but the first decision is whether it should be manual or mechanical. In general, preference is given to machinery in high cost technology projects because the original reason for constructing them in that way was influenced by the scarcity of labour and the availability of technically skilled personnel. On the contrary, low cost technology projects should rely as far as possible on manual labour. As far as technically and economically feasible, maintenance should be by local labour and only where it is not possible is resort made to machinery, particularly since most of the irrigation projects are in areas where labour is plentiful. In some cases, there may not be sufficient labour to undertake the requisite amount of work in the time available and thus the use of machinery becomes unavoidable. This is the case in Egypt where a period of one month (January) is available for maintenance.
As there are many maintenance activities, it is not always possible to have the ideal machine for each specific activity. Therefore, versatile machinery is preferable to highly specialized.
Table 2 OPTIMUM MAINTENANCE CYCLES1
|
|
Type of Canal |
Maintenance Cycle (years) |
||
|
IRRIGATION CANALS |
||||
|
|
|
Low silted water |
High silted water |
|
|
Silt clearance |
A |
8 |
3 |
|
|
B |
7 |
3 |
||
|
C |
6 |
3 |
||
|
D |
4 |
2 |
||
|
E |
3 |
2 |
||
|
Weed clearance |
A, B, C, D, E |
1 |
||
|
Reshaping of berms |
A, B, C, D, E |
3 |
||
|
Structures (metallic) |
|
|
||
|
|
Large structures |
6 |
||
|
|
Small/medium structures |
3 |
||
|
DRAINS |
||||
|
Silt clearance |
A, B, C |
6 |
||
|
D, E |
4 |
|||
|
Weed clearance |
A, B, C, D, E |
1 |
||
|
Structures (all types) |
|
3 |
||
|
DAMS |
||||
|
Weed clearance |
1 |
|||
|
Soil conservation works |
4 |
|||
|
Masonry |
4 |
|||
|
Gates |
2 |
|||
|
Electric engines |
1 |
|||
|
|
- revision |
1 |
||
|
|
- overhaul |
5 |
||
|
ROADS |
||||
|
Weed control |
1 |
|||
|
Road reshaping |
1 |
|||
|
Maintenance of road berms |
4 |
|||
|
Structures |
4 |
|||
1 Standards used by SARH (Secretaría de Agricultura y Recursos Hidráulicos, Mexico).
The machinery or manpower requirements can easily be calculated once the output of the machinery or labour for a given maintenance task and the amount of work to be done are known. The productivity of manpower and machines for the most important activities are discussed below.
i. Silt clearance
Silt is still removed manually in many parts of the world, provided that the water levels in the canals can be lowered sufficiently or, even better, the canals dried for several days. This method is quite effective, although the actual organization of the work can be a problem. Labour, its organization and supervision are discussed in section 6.6.
Where water-borne diseases are known to be prevalent, the use of labour should be restricted to those canals that can be dried completely for several days, otherwise mechanical means should be adopted.
Productivity of labour is generally low due to the muddy conditions in which they often work. Although some effort has been made to increase productivity by developing more appropriate tools like dredging scoops, specially designed digging hoes and forks, traditional tools (head baskets and shovels) are still used and productivity remains low. Output therefore varies widely from 2 to 8 m3/manday, depending on several factors such as working conditions, tools, lifting and hauling distance.
Several types of machines are utilized for silt removal and canal reshaping. The productivity depends largely on how well suited the machine is to the particular work. As already mentioned, only large irrigation schemes are likely to have specialized machinery for each type of maintenance work. Table 3 rates the productivity of machinery most commonly used for removing canal silt and reshaping, but most of these machines can do a certain amount of weed clearance at the same time, which affects their productivity. The given rates are applicable to medium or small size canals and refer mostly to dry working conditions. The output will be reduced by 20-30 percent under wet conditions except for the machines (dredgers) specially designed to work in running water.
The selection of machinery is mainly influenced by its reach and working conditions: wet or dry, accessibility, amount and type of work, weed infestation, etc.
Table 3 MACHINERY FOR CANAL CLEANING*
|
Type |
Productivity |
Characteristics of use |
Remarks |
|
Dragline excavators: |
|||
|
(a) small (0.3 m3)
|
80 m/day1/ |
· works from the canal banks on dry or running channel |
Versatile machine adaptable to several jobs and working conditions. |
|
120 m/day2/ |
|
Spoil can be dumped clear of canal banks. |
|
|
300 m/day3/ |
· reach: 9-10 m |
Care needed to avoid damage on compacted bed channels. |
|
|
|
|
To be used when desilting job smaller than 3000 m3/km of canal. |
|
|
(b) large (1 m3)
|
100 m/day1/ |
· works from canal banks on dry or running channel |
Similar to small dragline excavator. |
|
160 m/day2/ |
· reach: 18-20 m |
Suitable for jobs greater than 3000 m3/km. |
|
|
500 m/day3/ |
|
|
|
|
Hydraulic excavators: |
|||
|
(a) back-actor type
|
800-1000 m/day4/
|
· digging depth: 5-6.5 m |
They are normally crawler mounted and all hydraulically operated. |
|
· reach: 6-8 m |
|
||
|
· works from canal bank for maintenance work or from the rear in construction of new canals |
|
||
|
· a great variety of buckets can be fitted |
More appropriate for construction of new canals. |
||
|
· can be used for desilting or weeding jobs |
Those mounted on rubber tyres require firm ground conditions. |
||
|
Hydraulic excavators: |
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|
(b) telescopic boom (Gradall Type)
|
1000 m3/day5/
|
· digging depth: 6-7.5 m |
Can handle several jobs but highly suitable for excavating new drains or canals and heavy maintenance work. |
|
· reach: 9-11 m |
|
||
|
· bucket can be rotated hydraulically |
Compares favourably with the small dragline. |
||
|
· tilt capacity is often 90° (other types only 45°) |
|
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|
Hydraulic backhoes: |
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|
(a) tractor mounted
|
300-600 m/day2/
|
· digging depth: 3.5-4.5 m |
More powerful and robust than trailer type. |
|
· reach: 5.5-6.5m |
Suitable for construction and maintenance work. |
||
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· slew: 180°
|
Normally associated with a front- end loader attachment. |
||
|
The most common type is the side shift which can be mounted at each side of the tractor. |
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Can be used effectively for excavation, desilting and weeding jobs. |
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|
Needs good footing. |
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(b) trailer mounted
|
200-400 m/day2/
|
· digging depth: 2.8-4.0 m |
|
|
· reach: 4.5-6.0 m |
Highly suitable and economic for maintenance work. |
||
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· slew: 180-190°. |
|
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· hydraulic pump of the hoe is driven by the drive-shaft of wheel tractor |
Can work in difficult positions, while prime mover remains on level standing. |
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Dredges
|
100-200 m/day6/
|
· good for use in marshy ground or canals that cannot be cleaned from banks. Also good for removal of soft weeds |
Highly specialized machine. |
|
· maximum depth: depends on model but for small dredges 2 m |
Useful for concrete-lined canals since no damage is produced when fitted with suitable skid plates. |
||
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· spoil (slurry) on nearest bank or collected in special pontoons |
Difficult to transport and to move in and out of canals. |
||
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· cable and winch system for locomotion needs strong anchorage points along banks |
|
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|
Flat bed ditchers (Briscoe type)
|
3000-5000 m/day7/ |
· operates within the waterway, towed by tractors from each side; therefore can only work on dry canals |
Needs powerful crawler tractors for towing (D6, D7). |
|
12000 m/day8/
|
· bed width: 1.2-4.2 m
|
Most ditchers have their own engine and hydraulic system. |
|
|
Experienced operator needed. |
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|
More suited for construction of new canals or reconstruction work. |
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|
Rotary digger
|
400-600 m/day8/
|
· bed width: 0.4-1.0 m |
|
|
· operates within the canal |
Powered by PTO of wheeled tractor. |
||
|
· suitable for quick removal of light siltation and soft weeds |
Works canal bed and batters simultaneously. |
||
|
Bulldozer
|
300-400 m/day9/
|
· spreading of excavated material. |
Also used for road maintenance, light deforestation and rough land levelling. |
|
· used as prime mover of attachments mentioned above |
|
||
|
Grader |
500-800 m/day |
· finishing of canal banks and spoils |
Better suited to road maintenance work and levelling jobs. |
Notes:
1/ With standard bucket and for heavy excavation.
2/ With light-weight bucket and for removal of silt and vegetation.
3/ With the weed bucket but does not include any cleaning of the batters.
4/ Refers to remodelling of badly silted canals,
5/ Equipped with the 2.4m wide bucket.
6/ Desilting of 1.5m wide canal. Rates for soft weeds are much higher,
7/ For normal cleaning operations towed by a D6 crawler tractor.
8/ Light cleaning operation, with wheeled tractor.
9/ Refers to spreading of excavated material with a -medium size machine (D6).NB: The equipment listed is the most commonly used but many specialized machines (pontoon mounted excavators, rotary brushes - tractor mounted, flushing machines, etc.) are also available on the market.
A combination of labour and machinery is particularly frequent in lined canals, where silt is removed and accumulated at certain points by labour and then removed by mechanical means.
ii. Control of canal vegetation
Weeds are normally removed by cutting, mowing or dredging. Emergent and submerged weeds are best cut near the base of the stem, leaving roots and rhizomes undisturbed. Weeds need cutting at regular intervals throughout the season and the interval varies according to the environmental conditions and species. In temperate zones during the summer, it is usually no more than four weeks. The stage of growth at which the plant is cut affects the rate of growth; cutting at an early growth stage tends to be more effective than at a later one.
Four main methods are used to control canal vegetation mechanical, (c) chemical, and (d) biological. The choice primarily on the availability of labour, the predominant environmental and economic conditions. (a) manual, (b) of method depends weed species, the
a. Manual
Much of what has been said for the manual removal of silt applies to this method of weed control. However, since it requires a little more skill, the choice of an appropriate hand tool is more important and will lead to relatively, high productivity. Table 4 illustrates some of the characteristics of these hand tools and their related productivity.
Table 4 HAND TOOLS FOR CONTROL OF CANAL VEGETATION
|
Type |
Use |
Dimension of Canal |
Productivity |
|
Scythe |
Submerged weeds + grass and reeds on banks |
Small canals up to 0.6-0.8 m depth |
15-25 m2/hour |
|
Sickle, grasshook |
Submerged weeds + grass and reeds on banks |
Small canals up to 0.75-1.25 m depth |
8-12 m2 hour |
|
Rake, fork |
Removing cut material, lifting floating weeds, removing algae |
- |
Highly variable depending on weed species and vegetation density |
|
Chain knives and chain scythes |
Submerged weeds + grass and reeds on banks |
up to 6 m width |
4-60 m2/hour (two or three labourers) |
b. Mechanical
There are many types of specially designed machines available for specific weed control purposes. In some cases, it is preferable to adapt a regular farm, tractor for use with different attachments. Rubber wheeled 40-60 hp farm tractors can travel along channel banks with a maximum slope of 1:3 percent using the PTO (power take-off) for the implement. This operation requires neither specialized operator nor training nor equipment. For slopes steeper than 1:3 percent, hydraulically operated machines are available. Tractor-dragged chains are more effective on steeper slopes. Two 60 hp tractors can easily handle channels 6 m wide. Mower and cutter attachments are used mainly for grass and reeds on banks of watercourses, while buckets are more appropriate for emergent and submerged weeds. Launches can be used for mowing and cutting emergent weeds on banks, if the size of the channel permits their passage. Boats with cutting attachments are particularly useful for large waterways of shallow depth (up to 2.5 m) and where floating vegetation prevails. Details and productivity of the different types of machinery are given in Table 5.
Table 5 SPECIAL CHARACTERISTICS OF POWER MOVED TOOLS FOR CONTROL OF CANAL WEEDS1
|
Type |
Attachment |
Use |
Outreach |
Productivity |
Remarks |
|
Tractor powered attachments or trailers
|
Oscillating grass cutter Bar |
Emergent weeds |
3-6 m |
1-2.5 km/hr2 |
Machines can only work on one side of the canal at a time (crossing places Industrial tractors (70-150 hp) increase outreach to 8 m. |
|
Rotary cutter |
Emergent weeds |
" |
1-2.5 km/hr2 |
needed to complete operation). |
|
|
Flail mower |
Emergent weeds |
" |
1-2.5 km/hr2 |
|
|
|
Chain, harrow |
Submerged + emergent |
Width: 2 m |
0.5-3 km/hr |
|
|
|
Hydraulic excavator with attachments
|
Oscillating grass cutter bar |
Emergent weeds |
horizontal outreach; 6-12 m depth: 3-5m |
800-1200 m/day2 |
Wheeled machines 1 metre less effective outreach than tracked machines. |
|
Rotary cutter |
Emergent weeds |
" |
0,1 ha/hr |
Can work on both sides of canal at same time. |
|
|
Flail -mower |
Emergent weeds |
" |
0,1 ha/hr |
|
|
|
Mud bucket |
All types |
" |
400-600 m/day3 |
|
|
|
Weed cutting bucket |
All types |
" |
600-800 m/day3 |
|
|
|
Dragline |
Weed rake Mud bucket |
Submerged + algae +emergent |
9-21 m (dragline throw) |
500 m/day3 |
Max. channel width depends on access and configuration of channel |
|
Large boats C10-15 hp)
|
Oscillating rigid knives |
Bank weeds + floating leaved plants + emergent weeds + algae |
Width; 6-10m |
1-4 km/hr with a width of cut of 1.5-2.8 m |
Max. depth of cut: 1.5-2.8 m$ min. depth of cut: 0.5-1.0 m;-max. riverflow velocity: 2.5 km/hr. |
|
Modified (T type) grass cutters |
|||||
|
Wilder 'D' shaped cutter |
|||||
|
Small boats C4-5 hp) |
Oscillating knives grass cutter |
" |
Width; 5-6 m |
1.4 km/hr with a width of cut of 1.0-1,8 m |
Max. depth of cut: 1.0-1.8 m; min depth of cut: 0.5-1,75 m; max. riverflow velocity: 2.5 km/hr. |
1 Adapted from Robson (1976) and other sources.
2 Covering a swathe of 1,5-2 m,
3 Refers to the complete cleaning of medium sized canals (5-6 m width),c. Chemical
Chemicals have been developed which can control weeds effectively and safely, provided that adequate precautions are taken. They also offer an economic system of weed control in certain circumstances. The use of herbicides should, however, be limited because of their possible adverse effects on the environment. It is known that some herbicides may affect the quality of water to the extent that it becomes harmful to humans, animals and crops. Therefore, they should be selected with care. Where their use may prove hazardous, it may be necessary to limit or even prohibit them. Table 6 gives a summary of some available herbicides and their use.
d. Biological
Biological control may become more important in the future in view of the disadvantages of other methods (high costs, danger to the environment). The most common method is the introduction of an animal, fish or insect which feeds especially on the problem plant. Recently, attention has been given to the use of the grass carp (Ctenopharyngodon idella) for the control of submerged weeds and, in some cases, it appears to be an economical and effective way of control.
The introduction of competing plants (grasses) has been tried but this is not appropriate in watercourses where the flow must be unobstructed.
Sometimes weed growth can be prevented by fluctuations in the water regime, for example, holding a canal dry for 3-6 days is most effective in the control of algae. In the Bhukra Irrigation System in India, a system was developed to drain the canals and let them dry for five days; this prevented weed growth for six months. However, the success of this method depends on the weed species.
iii. Road maintenance
Road maintenance is work well suited to execution by labour, although hauling base and sub-base materials over distances greater than 200 m and compacting are operations more appropriate for mechanical means. There are several useful combinations of labour and machinery that depend on the local wages and availability of machinery.
Table 7 gives some generalized information on the machines most commonly adopted for road maintenance. Motorgraders, complemented with a water bowser and roller, are particularly useful for remodelling macadam and dust roads. Tipper trucks combined with loaders are normally used to haul base material for distances over 500 m, which is usually the case. The scraper is more suitable for short distances but there is rarely opportunity for its use in road maintenance work. Medium size bulldozers are also useful in some of the remodelling work before a grader can be used efficiently.
Table 6 SELECTED HERBICIDES FOR CONTROL OF AQUATIC WEEDS1
|
Type |
Use |
Dose |
Safety interval2 |
Remarks3 |
|
Aromatic solvents |
Submerged weeds |
40-80 ppmv4 |
- |
Inject under water. Toxic to fish. Distasteful in water |
|
Acrolein |
Submerged weeds |
4-7 ppmv |
- |
Inject under water. Very toxic to aquatic fauna |
|
Amitrole-T |
Floating + emergent weeds |
1-1.5 kg/ha |
- |
Spray on foliage. In USA can only be used in drainage canals |
|
2,4-D amine salt |
Broad leaved plants near water |
2-4 kg/ha |
3 weeks |
Spray on foliage, especially for water hyacinth |
|
2,4,5-T |
Ditch bank control (woody vegetation) |
4 kg/ha |
- |
Spray on plants |
|
Dalapon |
Aquatic grasses + cat-tail |
10-25 kg/ha |
5 weeks |
Spray on foliage, repeat applications. Safe to fish |
|
Diquat |
Submerged + floating weeds |
1-1.5 kg/ha |
10 days |
Spray on foliage. Considered safe at recommended dosages |
|
Dichlobenil |
Submerged + some floating weeds |
1 mg/1 |
4 weeks |
Spray on foliage. No adverse effect on wild life. At high concentrations can be toxic to fish |
|
Copper sulphate (CSP) |
Algae |
1.0 ppmw5 |
- |
Toxic to fish, distasteful in water when suggested dose exceeded |
|
Sodium arsenite |
Submerged + floating weeds |
4 ppmw |
- |
Inject or spray, highly toxic (0.02 g may kill a man) to mammals. Its use is discouraged |
|
Endothall |
Submerged weeds |
1.5-4 ppmw |
7-25 days |
Inject underwater. Some of the salts (long chain type) are toxic to fish and mammals |
|
1 Thomson (1976), Unesco (1974) and other sources | ||
|
2 Before use of water for irrigation | ||
|
3 Time to spray one hectare: |
Hand operated back sprayer, 10 litres capacity |
- 9 hours |
|
|
Back mounted power sprayer |
- 6.5-7 hours |
|
|
Tractor mounted boom sprayer |
- 4-5 hours |
|
4 ppmv = parts per million by volume | ||
|
5 ppmw = parts per million by weight | ||
Table 7 MACHINERY USED FOR ROAD MAINTENANCE AND LAND GRADING AND RELATED PRODUCTIVITY1
|
Type |
Productivity |
Optimum hauling distance |
|
Bulldozer (130-150 HP) |
400 m3/day |
100 m |
|
Grader |
1000 m/day |
50 m |
|
Tipper truck2 |
300m3/day |
500 m or more |
|
Loader/shovel (1.2 m3 bucket) |
300 m3/day |
20 m |
|
Scraper towed (12.0 m3 bowl) |
1100-1200 m3/day |
100-250 m |
|
Motor scraper (12.5 m3 bowl) |
1100-1200 m3/day |
250-500 m |
|
Tyre or sheep foot roller |
800-1000 m3/day |
|
|
Water bowser |
1000 m3/day |
|
1 Productivity figures are only an approximation; precise indications can be obtained from dealers when working conditions are known.2 Used in combination with loader or shovel.
iv. Cleaning tile drains
Tile drains are usually cleaned by mechanical means and flushing, although sometimes chemical methods are necessary to remove mineral deposits.
a. Mechanical
A hard PVC hose or rod of bamboos screwed together is pushed into the drain. A device is attached to the end of the rod or hose to stir up the dirt and/or remove it from the drain. Different attachments can be used, e.g. iron lamellar flaps, hollow pipe or brushes. This method will remove sand, roots and mineral deposits. Its disadvantage is that only a small quantity can be removed at one time.
b. Flushing
This method consists of pumping water under pressure into the drain, thus removing the dirt by jet action. It can be done with a high pressure nozzle (80-100 atmosphere) delivered from a farm tractor of about 40 hp, or with a low pressure nozzle (20 atmosphere) delivered from a movable motor; 1000 m/day of tile drain can be cleaned with this machine. Its disadvantage is that it only removes a small portion of the silt and in sandy soils there is the risk of sand entering the pipes. With this method drains of up to 350 m can be cleaned.
c. Chemical
Mineral deposits can be removed by injecting SO2 at the upper end of the drain. Finding the upper part of a drain is not easy if it has not been properly marked previously. A convenient practice is to connect the upper end of a drain to a stand pipe. The cleaning must be carried out in wet conditions and the drain closed for about 24 hours after the appearance of the gas at the outlet.
Costing the intended maintenance programme is an easy operation because the amount of work to be done has been determined and the basic unit prices are known. It may be important to present a detailed justification for some of the intended works emphasizing the consequences (financial and social) if they are not carried out. It is also advisable to earmark some funds for unexpected repairs. About 10-20 percent of the total budget for this purpose is generally accepted.
As in any budgeting operation, the initial estimates may have to be reconsidered and curtailed in relation to the finances available. This is often the case in public irrigation schemes, where allocated funds are considerably lower than those requested. At this point, the establishment of priorities is an important exercise in which all the units of the water management organization should participate. The maintenance programme is usually adversely affected by this kind of budgeting exercise because the effect of reducing the level of upkeep is not apparent in the short run. The establishment of maintenance priorities depends on many factors such as reduction of manpower and machinery, etc., and is therefore site specific.
The implementation of maintenance activities is highly site specific in nature, but some general management principles can be applied, the most relevant of which are as follows:
a. Good planning is particularly important in maintenance work since the time and resources available for its execution are limited. The use of planning techniques such as critical path methods and bar diagrams, is helpful, though rarely put into practice.b. Monitoring the output productivity is essential, not only to feed back the planning process with realistic data but also to control the progress of the work planned.
c. Farmers' participation in maintenance work should be encouraged. In some irrigation schemes the contribution of a number of mandays per farmer is spelled out in the by-laws of the scheme. In other cases the responsibility may be for specific studies of irrigation ditches. The Maintenance Service should provide technical guidance, organize and control the work.
d. Maintenance work on a voluntary basis is customary in some old irrigation associations but it is difficult to obtain in public irrigation schemes. In this latter case, the use of incentives such as food and transportation, is advisable and work should be restricted to special repairs that need unexpected large human resources.
e. Whenever unskilled labour is required, use should be made of the human resources of the farming community of the project.
f. Subcontracting part of the maintenance work may be advisable in certain circumstances and should be more frequently adopted. It reduces the number of permanent staff in a maintenance unit and is a system that can be adapted to maintenance conditions that change from one year to another. It is highly suitable for specialized jobs such as maintenance of electro-mechanical equipment of gates and remote control devices, placing and removing deep well pumps, etc. Irrigation schemes having few vehicles and machines should also consider the possibility of subcontracting their maintenance rather than having a poorly equipped workshop where maintenance may be of low standard.
6.6.1 Labourers
6.6.2 Ganger or headman
6.6.3 Overseer
6.6.4 Work inspector
6.6.5 Machine operators
6.6.6 Mechanics
6.6.7 Chief of maintenance
A maintenance service needs the following kind of personnel:
1. Labourers
2. Ganger or headman
3. Overseer
4. Work inspector
5. Machine operators
6. Mechanics
7. Chief of Maintenance.
Most of the maintenance workers are unskilled labourers. The basic unit is the gang consisting of 8-20 labourers under the supervision of the headman or ganger. The number of labourers required for a maintenance task varies widely since it depends on many factors: type of work to be done; labour/machinery substitution policy of the irrigation scheme; working conditions, etc. Table 4 and section 6.4 provide some standards for labour but requirements will depend on local conditions. Unskilled workers are seldom part of the permanent staff of a scheme, they are contracted for periods of time to undertake a certain task.
Skilled labourers are also needed for certain jobs such as pipe laying, masonry work, etc. They are often contracted on a piece-work system. Since such people are not easily available in the rural areas, it is advisable to have a number of them as part of the scheme's permanent staff, provided enough work is available for them throughout the year.
The headman is usually one of the workers and quite often elected by the group either because of natural leadership or on traditional grounds. Essentially, his function is to enforce discipline and to ensure that productivity targets are met. For most activities no special training is required; he need not be literate and his rate of pay is marginally higher than that of an unskilled labourer. As said earlier, he supervises a group of 8 to 20 labourers.
When maintenance is undertaken mainly by labour, the overseer has the function of controlling the work of a group of 5-10 gangs. The more specialized the task, the smaller the group of gangs that can be controlled. In some countries, where labour intensive methods are currently used, the labour gangs and their overseers are provided by small contractors who are given contracts for specific tasks.
In other circumstances, when the operation and maintenance of a scheme are undertaken by a single unit, this responsibility is given to the water guard or ditchrider because most of the maintenance is done during the slack season.
a. Job description:- organize and control the work of the group
- ensure proper standards of workmanship and productivity
- keep records of hours worked and work done
- maintain an adequate supply of materials and tools.b. Qualifications:
The overseer is normally selected from the gangers because he has shown greater initiative and capability of leadership. He must be literate and have an understanding of work measurement. Secondary school level is desirable. In irrigation schemes where most of the equipment is mechanical, the overseer is normally a qualified machine operator promoted to this position after some years of work and having shown leadership capabilities.
c. Manpower requirements:
One for 5-10 gangs (labour-intensive)
One for 3-5 machine operators (capital-intensive).
Within a maintenance unit he is the key person upon whom depends the achievement of a good standard of maintenance. He is the man concerned with periodical supervision of items that may need maintenance, the preparation and estimation of work to be done and the supervision of the actual work at the site.
a. Job description:- inspect periodically the state of the physical system (canals, roads, buildings) and prepare estimates for the maintenance needed- report to the Maintenance Chief on the repairs needed
- set up the work to be done either by labourers or machinery
- measurement of work accomplished
- ensure that proper technical standards are achieved
- ensure that safety measures (in the use of machinery and chemicals) are followed.
b. Qualifications:
Work inspectors are usually promoted to this position having risen through the ranks from a manual labourer or an operator. They must have considerable supervisory capacity, as well as technical skill. People that have risen from the ranks have seldom had the opportunity to acquire technical skills; however through in-service and other training their abilities and qualifications can be improved.
c. Manpower requirements:
A work inspector is usually appointed for each group of 4-6 overseers.
Most of the equipment used in maintenance work (draglines, hydraulic excavators, motorgraders, trucks, loaders) is expensive and hence operators must be fully qualified. Productivity with the same machine varies widely, depending on the skills of the operator. Furthermore, the working life of a piece of equipment will rely largely on its proper handling and routine maintenance by the operator.
a. Job description:- operate the equipment assigned
- undertake regular maintenance of the equipment assigned
- report the work undertaken and completed to the work inspector
- report the fuel and oil consumption
- report any incidental damage or breakage.b. Qualifications:
Technical school with five years' experience in the operation of the equipment used in maintenance work.
c. Manpower requirements:
One operator per machine is the norm; however, if the machines are not in simultaneous or daily use, one operator can be assigned to 2-3 machines. Where it is necessary to complete maintenance within a very short period of time, 2 or 3 turns per day are established to keep the machine working the maximum possible number of hours per day.
Qualified mechanics are needed to repair the equipment. They are part of the staff of the maintenance workshop.
a. Job description:
Overhaul, repair and service the equipment used for maintenance work.
b. Qualifications:
Technical school with five years' practical experience in diesel engine and maintenance equipment repair.
c. Manpower requirements:
These vary widely depending on the functions of the workshop. The most common case is that the workshop does only simple repairs and major ones are sent to specialized workshops. If such is the case, a group of 2-3 mechanics with an equal number of helpers or apprentices can handle a machine plant of 20-30 units.
Apart from the general duties of administering and organizing the maintenance work, the following tasks would also be his responsibility:
a. Job description:- evaluate annually the maintenance work needed- plan maintenance work in sequential order to achieve maximum utilization of available resources
- prepare technical and economic specifications of the work to be undertaken by contract
- order, account for and issue tools and materials
- supervise the upkeep of equipment approve payment of contracts
- issue instructions to subordinates on the work to be done
- report on maintenance costs to the scheme manager.
b. Qualifications:
BSc degree in Engineering and 5 years experience in irrigation engineering. Experience in maintenance of irrigation schemes is desirable. The ability to organize and direct people is also an indispensable requirement.
c. Manpower requirements:
A Chief of Maintenance is necessary for any irrigation scheme over 10000 ha. For smaller schemes, the functions of a chief of operations and maintenance can often be combined in a single person. For schemes over 50000 ha, it is advisable to have an Assistant Chief of Maintenance for each unit of 30000 ha who is, in turn, supervised by the Chief of Maintenance for the whole scheme. A Chief of Maintenance is assisted in carrying out his functions by various auxiliary staff (record and store keepers, secretarial services, drivers, etc.) as appropriate to the size and complexity of the scheme.
For medium and small irrigation schemes (up to 20-40000 ha), it is common that the services of operation and maintenance are put together in a single unit. Responsibilities for operation and maintenance work often coincide in the same person and it is difficult to differentiate the 'maintenance service' as such; at the most there is a small unit mostly concerned with repair and overhaul of machines. Since operation activities are concentrated during the irrigation season and those of maintenance in the off-season, it would be logical to use manpower best by combining these activities in the same unit. However, there are also occasions when this arrangement is not suitable; for instance: (a) in many arid regions the irrigation season lasts 9 to 11 months, leaving too little time for the operation personnel to occupy themselves with maintenance; (b) there are schemes in such a bad state of repair that maintenance care throughout the year is needed to keep them functioning, without deflecting attention to operational matters.
Whenever operation and maintenance are together in the same unit, some of the maintenance responsibilities are added or combined with those of the operation personnel; for instance, the water guards can also act as overseers, the water master can act as a work inspector, and the Chief of the Unit would cover operation and maintenance responsibilities. The organizational structure for maintenance activities is parallel to that of operation since, virtually, they are undertaken by the same staff. Therefore, the organization by areas and sections of the scheme, as indicated in Figure 11, prevails.
For large irrigation schemes, or whenever the maintenance activities are sizeable enough to justify full occupation of the staff throughout the year, the usual organizational pattern is to separate the operation and maintenance units. In this case the maintenance service can be organized in two ways:
i. by specialized maintenance units
ii. by areas (sections of the irrigation scheme).
The organization by functions is more suitable where there is a heavy reliance on specialized machines, i.e. in high cost technology projects and where labour is scarce and expensive. In less developed areas with greater reliance on manpower and poorer communications, a decentralized, area-based approach is likely to be more efficient. The two alternatives are briefly discussed below:
i. Organizational structure by functions: The basic idea is that by organizing small units specialized in a certain type of work, such as desilting and cleaning of small and medium canals, cleaning of tile drains, road maintenance, etc., higher standards of efficiency should be achieved. The size of the specialized unit in terms of manpower and machines is determined by the standard outputs which can be achieved under the local conditions and the cycle of maintenance for the particular work. Each unit is supervised by a work inspector and the work of all the units is programmed and controlled by the Chief of the Maintenance Service. Wherever the number of operators to be supervised is too large (more than 8-10), the unit should be organized by sub-units headed by an overseer (the most experienced of the operators) and the sub-units supervised by the work inspector. Figure 12 illustrates an organizational structure of this type where all the work is undertaken by machines.ii. Organizational structure by areas: The scheme is divided into suitable sections as far as maintenance is concerned. The size of the section is quite variable and depends on the means available to undertake the work and the configuration of the scheme. As a guiding rule the whole maintenance of the section should be completed in a cycle of 3 years. A size of 10-15000 ha often meets that condition. For each of the sections a work inspector is appointed who is responsible for organizing the maintenance work as if the section were an independent scheme. In order to supervise the different activities he is helped by a number of overseers, who in turn are responsible for organizing the different maintenance tasks (desilting of canals, cleaning of drains, repair of roads, etc.). This system is often complemented by a pool of specialized machinery which, at the request of the section, is used for specialized jobs. Figure 13 illustrates an organization of this type where the work is undertaken by labourers. Between the two cases outlined in Figures 12 and 13 there are other possible combinations.
Fig. 12 Organization of a Maintenance Service by main functions
Fig. 13 Organization of a Maintenance Service according to irrigation areas
