5.1 Main objectives of an operation service
5.2 Planning the operation
5.3 Distribution of water (implementation)
5.4 Monitoring the operation
5.5 Staffing the operation service
5.7 Organizational structure
It has become a matter of increasing concern in recent years that the performance of many irrigation schemes has fallen short of expectations. This is due to a number of factors but no doubt the lack of proper operation and maintenance is an overriding cause for the malfunctioning of schemes. It is always surprising to find that while planning, design and construction of irrigation schemes receive considerable attention and are generally carried out with great care, little attention is paid to operation and maintenance matters.
There are three fundamental causes for the poor operation of an irrigation system:
i. lack of technical skills in planning, implementing and monitoring the system;
ii. poor man-management;
iii. technical deficiencies in the physical system.
This chapter is mostly concerned with the technical skills necessary for suitable operation of an irrigation scheme. For this purpose it analyses the different water distribution methods with their advantages and disadvantages. It also considers the two main alternatives for organizing an operation service and describes the necessary skills of the required manpower.
The main problems related to poor man-management, such as minimization of corruption, friction between farmers, lack of incentive for the operational personnel to do a good job, have already been discussed in Chapters 3 and 4. Insufficient manpower is also a management problem which can cause serious repercussions in irrigation operations. For this purpose, standard manpower requirements for the main activities are given in this chapter.
Technical deficiencies are either the result of poor maintenance, which is discussed in Chapter 6, or faulty design. Remedying a faulty design requires major rehabilitation work which has to be properly studied and designed.
There is a tendency to believe that out of the three fundamental causes outlined above, those related to technical deficiencies are the main ones responsible for a low efficiency. Although any generalization in this respect may be risky since exceptions are bound to exist, the chief reasons for low efficiency are more often related to lack of technical knowledge among the people operating the system and man-management issues than to technical deficiencies in the system.
In order to illustrate the extent to which deficiencies in the operation procedures may adversely affect performance, a recent experiment in the Philippines is quoted. In this experiment, conducted by members of the International Rice Research Institute on a canal-irrigated command of 5700 ha, it was found that the introduction of quite modest changes in water distribution procedures was associated with a 97 percent increase in the production of the system overall, and a 1494 percent increase in the tail section of the system, over a two year period. Before the intervention of the study team there had been a familiar pattern of over-irrigation at the head of the system, with insufficient supplies remaining for the tail. Official control over water appropriations had been poor and there was widespread uncertainty among the farmers about the likely timing and quantity of water supplies. The experiment was carried out without the introduction of any physical improvements (Valera and Wickham 1976).
Other interesting evidence has been recorded in Sri Lanka and Pakistan. In the Sinhalese case, the introduction of improved management in a small reservoir system of about 5000 ha enabled a level of production to be reached which was about 50 percent higher than it would have been under normal conditions. In Pakistan, a sample survey revealed very high average water losses within the watercourse command, a substantial proportion of which could be attributed to poor main system operation.
Nevertheless, it is obvious that any serious attempt to evaluate the operation of any given irrigation scheme must take a close look at the three groups of problems if suitable improvements are to be achieved.
An Operation Service has as its chief objective the timely delivery of the irrigation water necessary to satisfy crop water requirements. The accomplishment of this objective implies the following main activities:
- Planning the Operation (preparation of the so-called Irrigation Plans)
- Implementation of the Plan (actual water distribution)
- Monitoring of the Operation (collection of data related to water use and preparation of the corresponding reports).
To undertake these tasks different kinds of personnel are required with specific qualifications depending on the type of water distribution system and other local characteristics. These functions and manpower requirements are examined below.
5.2.1 Estimating future water supply
5.2.2 Estimating water demand
5.2.3 Matching supply and demand
5.2.4 Restrictive measures to match supply and demand
The object of this activity is to match supply with demand as closely as possible. The planning exercise may be a complex and laborious undertaking, as is the case when preparing "Irrigation Plans" for large canal systems, or just a simple meeting where farmers are informed of the amount of water available and the times when it will be distributed. The complexity or simplicity of the planning process varies from case to case depending on the scope for manipulating supplies to meet demand, but planning is essential in all cases (and two-way communication with the farmers). As water is a scarce resource in irrigation schemes, the importance of this planning process cannot be overemphasized, but unfortunately there are too many occasions when this process is not carried out even in its most elemental form.
The preparation of an Irrigation or Crop Plan implies the following main steps:
- Estimating future water supply
- Estimating water demand of the expected cropping pattern
- Matching supply and demand.
The estimation of the future water supply may be a fairly straightforward calculation or a rather complicated one, depending on several factors such as the characteristics of the dry and wet season, the type of water storage utilized, the reliability of climatic data, or the effective rainfall during the irrigation season.
Simple cases of determination of the water supply are: (a) pumping or diversion from a river, with an average flow much greater than the one pumped; (b) pumping from fairly abundant aquifers; (c) dam storage where the season for filling the reservoir does not coincide with the irrigation season during which hardly any water contribution can be expected. In all these cases the available water resources are known precisely at the beginning of the irrigation season.
However, there are many other cases in which a certain degree of uncertainty exists about the availability of the water resources. In these, the management of the project should make its projections on the basis of conservative estimates, i.e. using a rainfall probability of 75 or 80 percent. The mathematical modelling technique, based on reliable climatic data, can also be a very useful tool to forecast the water available for different levels of risk. In any case, it is most important in these circumstances to have alternative plans which can be adopted according to changing climatic conditions. In other words, rather than a fixed plan, a dynamic programme is necessary which can be modified according to changes in the weather. Technically; this is quite feasible, but the usual bottleneck is the rapid transfer of this information to the farmer, so that he can adjust to the changing conditions.
The water demand is basically determined by the expected cropping pattern and the irrigation efficiencies at the farm and project level.
i. Cropping pattern
The difficulty of foreseeing the expected cropping pattern on an irrigation scheme varies according to the degree of freedom allowed to farmers in their choice of crops and the timing of their cultivation activities. It is least difficult under conditions of land settlement projects with an integrated management: the government through the operating agency controls the cropping pattern (and, often, the timing of certain cultivation activities, e.g. mechanized land preparation). Alternatively, demand can be controlled by means of differential control over the water supply pattern (permitting certain highly water-consuming crops to be grown only in certain designated areas which will be the only ones to receive sufficient water); or legal limits can be placed on the areas to be covered by certain crops (with fines being exacted for contravention of the rules). Or, finally, there can be a free choice of cropping, when response to market demand will be the main determining factor.
These restrictive measures will be discussed in greater detail under 5.2.3.
In irrigation schemes where the management has recognized authority over the cropping pattern, a good method to keep a balance between the cropping pattern desired by the farmers and the management is the use of approval or rejection forms. The farmer proposes a cropping pattern which is examined and computed by the project management in terms of water requirements. The farmer is informed whether his proposal has been rejected, approved or slightly modified. In the case of a rejection, the farmer must propose another cropping pattern. If rejected again, the dispute can be settled by a special committee of appropriate representatives.
On the contrary, in irrigation schemes where the management has no authority over the cropping pattern, information must be gathered from statistical data from previous years and study of the trends in relation to expected prices of different crops. This kind of data should be gathered in the Operation Service office, but sometimes it is collected by other government offices; for instance, in the Indian subcontinent, cropping patterns are often recorded in detail by the land and water revenue officials.
To make accurate calculations of monthly project water requirements, information is needed not only on the expected cropping pattern but also on the actual water requirements (which will vary according to the stages of crop growth) of different crops under different soil conditions. This basic agronomic information is often not available to (or used by) system operators (particularly where Irrigation and Agriculture belong to two separate organizations). This emphasizes the need for a small planning unit - at least in a large project - within the Operation Service where such data are collected and processed effectively.
Once all these data are known, the calculation of the monthly crop water requirements must be made. A variety of well known formulae exists to undertake this exercise. Those described in Irrigation and Drainage Paper No. 24 (FAO 1977) and the methodology followed therein are recommended. Calculators and small desk computers can be valuable tools for calculation.
ii. Irrigation efficiencies
To complete the evaluation of the demand, the efficiency of the water distribution system and of application must be known. This is usually the weakest point in estimating the demand, because such evaluations are rarely made in the field as they are time-consuming and the qualified staff needed to undertake them are frequently not available. This again stresses the need for some specialized unit to take care of this important function. These functions could be integrated within the formerly mentioned "planning unit" or in the Irrigation Assistance Service (see Chapter 7), depending on local circumstances, but the important thing is that they are carried out by someone.
In the absence of reliable field data on efficiencies, empirical data from the abundant literature on the subject can be used.
Once calculations regarding the supply and demand have been completed, the most difficult part of the exercise begins: to decide on water distribution practices or other measures which allow the closest possible matching of supply and demand. Before discussing such practices and measures, it is useful to recall the most common situations that can be found in matching supply and demand. Although the spectrum of possible situations is very large, three main cases can be clearly distinguished:
i. Irrigation schemes where water supply is greater than or equal to the demand.
ii. Irrigation schemes with a moderate water deficit.
iii Irrigation schemes with a large water deficit.
i. Irrigation schemes where water supply is greater than or equal to the demand
This is the most favourable situation from the management point of view. Although systems with relatively abundant water are easier to operate, they are likely to be less efficient in terms of returns per unit of water distributed than systems with some degree of scarcity. This kind of situation often corresponds to the construction period of very large irrigation schemes in which, until their completion, demand is considerably lower than supply. It is also typical of incomplete schemes.
In technically well designed schemes, supply and demand should match fairly equally. However, it is not only important to check the seasonal volumes needed but also to check if the demand in the peak month can be met. When the supply is smaller than the peak month demand, the usual corrective measure is to advance the planting dates of some of the crops in order to avoid coincidence of peak demands.
ii. Irrigation schemes with a moderate water deficit
A moderate water deficit (10-20 percent of the water supply available) is often encountered in irrigation schemes. This can either be a periodic situation found only in "dry" years or recurrent every year. In the first case, it is normally an accepted risk in the design of an irrigation scheme, while in the latter it can often be attributed to designs associated more with social factors than technical ones, although other factors (changes in planned cropping pattern, overestimation of the potential water supply, technical deficiencies of the system, etc.) may also have led to this kind of situation. Whichever the case may be, these irrigation systems offer the best potential for maximizing the returns from the water that is available.
Suitable water distribution practices and methods, combined with some of the measures pointed out below, can be extremely useful in matching, as far as possible, supply and demand in these schemes.
iii. Irrigation schemes with a large water deficit
There are many irrigation schemes, particularly in the Middle East and Indian subcontinent, which command an area much larger than can actually be irrigated. The water deficit is often greater than 50 percent of the available supply. However, these schemes were not designed to irrigate the whole command area at cropping intensities of 100-200 percent. In their case, 'demand' may be fulfilled if 40-60 percent intensities are achieved.
Many of these schemes were designed with the important social objective of benefitting as many people as possible; others were merely the result of an underevaluation of crop water requirements; still others were aimed at maximizing government revenue. Whatever the reason, these projects have frequently yielded less than expected. Production per hectare is low and large areas are sometimes abandoned due to salinity problems. Some of the reasons for such a state of affairs were:
- that although the efficient use of water was essential, the farmers were not assisted in preparing their lands (land levelling, grading) for efficient use when water supplies were limited;
- the same can be said about irrigation practices suitable for salinity control and efficient water use;
- that no preventative measures (drainage system) were taken to prevent build-up of soil salinization;
- that the water distribution network was much longer than it should have been; therefore losses were bound to be greater.
These problems do not only occur in irrigation systems with large water deficits; they can also happen in any of the others. The crux of the matter is that under very limited water supply, these problems are likely to have more damaging effects.
Some of these problems can be corrected a posteriori through the rehabilitation and improvement of the scheme, although this entails greater difficulties and costs than if the project had been suitably designed and operated from the beginning. The point to be made here is that where water supplies are extremely scarce in "socially designed projects", it is possible to obtain high returns from water, provided good management (i.e. ensuring regular and predictable water supplies) is ensured, suitable technical designs are implemented and the farmer is assisted to use water efficiently.
Several restrictive measures and water distribution practices can be utilized by the project management to reduce the gap between supply and demand. Obviously such measures apply mostly to situations described under (ii) and (iii) of 5.2.3.
The measures that can be taken to reduce the water deficit are related to:
i. the cropping pattern
ii. the water distribution practices
iii. the water fees.
They are not mutually exclusive and a combination can usually be recommended.
i. Measures related to the cropping pattern
There are three main measures that can be undertaken to reduce water demand: (a) changing the planting time; (b) changing the existing crops for others with lower water requirements; and (c) reducing the irrigation area. Of all the possible measures these are the most effective to reduce water deficit but they are also the most difficult to implement. They require that the management of the irrigation scheme be invested with the necessary authority to introduce such changes in the cropping pattern. Otherwise a long dialogue may take place between the management and the farmers to convince them of the necessity for this measure which may not always end with a positive decision.
a. By suitable regulation of the planting time and other cultivation activities large reductions can be attained during the peak demand of an irrigation scheme. For instance, in Taiwan (Province of China) water supplies are very carefully varied according to the stage of crop development and farmers know that in order to obtain enough water at periods of peak requirements (for land preparation, etc.), they must keep to a pre-planned timetable. Careful planning of this kind also allows controlled staggering of cultivation activities between different sections of the same irrigation system leading to a more rational use of available machinery and manpower.
b. Changing the existing crops for others is an effective measure to reduce water demand, e.g. clover for alfalfa, sorghum for maize, etc. However, the condition must be met that the two crops have similar characteristics or end purposes. Otherwise there is the risk of introducing crops which may have very low water requirements (soybeans, groundnuts, etc.) but that are not financially attractive to the farmer. Therefore the possibilities for applying this measure are limited.
c. Reducing the irrigated area is the most expedient way of reducing the demand, but it is difficult to implement. Rather than physically reducing the irrigated area, the usual measure is to reduce the water allocation which in turn should lead to a reduction in the area irrigated by the, farmer. However, the farmer often decides to take a risk and instead irrigates a much larger area than technically feasible. As pointed out earlier, with suitable levelled land and using good water management practices, the risk taken by the farmer might yield high returns - but unfortunately this is rarely the case.
Other methods of reducing the cropped area are:
- eliminating the areas furthest from the distribution point (quite common in small tank schemes in S. India and Sri Lanka, where the farmers may have fragmented holdings some near the tank, others farther away);
- giving water to certain sections of the command area only, with the sections being rotated from season to season. This is only feasible where irrigation is supplementary and farmers in sections not receiving irrigation water are able to grow rainfed crops in the season concerned.
ii. Measures related to water distribution practices
There are only two measures that can be used to lessen the water deficit:
(a) reducing the water allocation but keeping the same water distribution method?
(b) changing the water distribution method to a more efficient one.
a. Reducing the water allocation can be effected in different ways:- by allocating water to preferential crops
- by decreasing the amount of water being given per irrigation
- by extending the interval between irrigations.
Allocating water to preferential crops: This is common where high value crops (fruit trees, nursery produce, vegetables) are grown near to less valuable ones. In such cases, the regulation is sometimes established that the valuable crops must receive their necessary allocation and whatever is left can be utilized for the other crops. This was the case in the Gezira Irrigation Scheme1 (Sudan) where the irrigation of cotton took precedence over any other crop. This kind of measure is easy to implement provided that the interests of the farmers and the management are the same, which is generally the case.
Decreasing the amount of water given per irrigation: This can be done in a manner proportional to the deficit with no regard to the possible effects on the crop yield or, on the contrary, by trying to decrease the amounts in such a way that the effect on crop production is minimized. The first alternative is the most commonly adopted because of its simplicity, but the second one offers much better possibilities, where it can be applied. An example calculation according to this latter alternative has been given in Annex II (Case b). The calculation is based on new developments resulting from studies made on crop yield response to water (FAO 1979). This method can be extremely effective in irrigation schemes concerned with one single crop, but its effectiveness decreases with the number of crops grown because the intervals that fit one crop well may not necessarily do so for others.
With measures like these, the reduction that can be expected in the water demand is moderate. Large reductions in flow in canals will often hamper their operation, e.g. the canals of northern India are designed to run above 75 percent capacity and will not distribute water proportionally if run below this figure.
Extending the interval between irrigations is the measure most commonly used to cope with water deficits. For example, if in one given year the system is able to provide 8 irrigations but the following year the supply is only half this amount, the system will deliver 4 irrigations at double intervals of time. Although this measure is most common, there is, however, as in other cases, also the possibility of giving the 4 irrigations at times when the crop can make best use of the water. As in the previous case, an example has been worked out in Annex II (Case a) using the same principles of crop yield response to water. Similarly, the effectiveness of the method is reduced by an increase in the number of crops grown in the scheme.
b. Changing the water distribution method: Among the different water distribution methods described in detail in the next section, it is to be expected that some will be more efficient (assuming comparable situations of management and technical design) than others. The possibilities of changing the water distribution method are very limited since a certain method is normally linked with a specific technical design.
In most cases, changing the method also means changing the physical system to some extent. However, even in cases where there is no need to alter the physical system, a switch is difficult to introduce because farmers have been used to a particular system for many years. When such changes are intended, it is advisable to try them out in a pilot area and later extend them to the rest of the system when the positive attributes of the new method have been demonstrated.1 This policy changed later because of a reduction in cotton prices on the international market and an increase in the water supply to the scheme.
iii. Measures related to water fees
Increases in the water fees tend to decrease the amount of water used. However, this measure should be exercised with great care and only where the preconditions for its use exist. One precondition is that the water distribution system must be equipped with water measuring devices at the farm level, in order that prices of water can be associated with the volumes received. Another important requirement is that the farmer must have some understanding of the soil-plant-water relationship, otherwise he will continue to use the same amount of water as before and simply pay more for it.
The possible effects of a large increase in water fees should always be studied carefully before actual implementation. There have been cases where a large increase was introduced but the farmers refused to pay, putting the management in a difficult position (see Chapter 8 for more details).
5.3.3 Canal rotation and free demand
5.3.4 Rotational system
5.3.5 Continuous flow
The actual distribution of water has different characteristics depending on the water distribution method utilized. The main water distribution methods are:
- On-demand: Water is available to the farmer any time that the intake or hydrant is opened. Therefore the amounts to be used are not limited but water consumption is usually metered and paid for by cubic metre.
- Semi-demand: Water is made available to the farmer within a few days (generally 2-7 days) of his request. The amount is often limited to a certain volume per hectare.
- Canal rotation and free demand: Secondary canals receive water by turns, for example every 7 days, and once the canal has water farmers can take the amount they need at the time they wish.
- Rotational system: Secondary canals receive water by turns and the individual farmers within a given canal area receive the water at a pre-set time and generally in a limited quantity.
- Continuous flow: Throughout the irrigation season, the farmer receives a small but continuous flow that compensates the daily crop evapotranspiration.
As stated earlier, the water distribution method is normally linked to the design of the conveyance system - although there are exceptions; therefore once a water distribution method has been selected there is little possibility to change it. The selection of the water distribution method is thus an important matter where social, technical and economic characteristics must be taken into consideration. Each of the methods has its own characteristics which may, or may not, suit local conditions. They are briefly discussed below.
On-demand irrigation systems are generally designed with high-level technology. The degree of human intervention is minimal since they operate on automatic principles, i.e. when the water level or pressure drops in a canal or pipe due to the opening of an inlet, the level or pressure is immediately reinstated by an automatic device which calls for a greater supply, provided by automatic gates or valves. The efficiency of these systems is very high (up to 90 percent) particularly when using pipes for the distribution.
There is very little actual operation in these systems and that is limited to some overall control of the automatic system, which is usually done through remote control panels located at the management office. Although the manpower requirements are small, the people must be highly qualified.
The great advantage of this method is that it allows the farmer to use the water when it is most necessary for the crops. The main disadvantages are high costs and the need for a high level technology in the construction and maintenance of the systems. Thus the systems are more suitable for developed countries than developing ones and rather unsuitable for the least developed countries.
The success of on-demand systems in developing countries depends on many factors but, in any case, the closed system (pipes) has better possibilities than the open canal system. The reason for this is that in the latter the automatic gates are susceptible to blockage by vegetation or misuse by human intervention and once the automatic regime of the canal is disrupted the chances of overtopping are great, with subsequent damage. On the contrary, pipe systems have the important advantage that they cannot be manipulated by anyone, and thus operational and social problems (e.g. stealing of water, etc.) are reduced.
This is perhaps the most common system of water distribution due to its simplicity. A farmer requests the water from the water guard, who passes the information up to the water master. He makes the necessary calculation to accommodate it with the demands of the other farmers within the limited capacity of the canal. If the demand can be met, the information is passed back through the water guard to the farmer with an indication of the exact time of his turn. In irrigation systems where the canals have been designed with a certain flexibility, the request is usually met within a short time (2-3 days), although sometimes 6-7 days can elapse in the case of canals with little flexibility and high demand.
The amount to be supplied to the farmer is usually fixed in relation to the number of hectares. A known amount of water is an indispensable requirement for such a system, otherwise the water master cannot calculate the time and flow needed for each request in order to prepare the water distribution programme.
This form of distribution requires a well-designed and constructed irrigation system since the flows delivered by the canals should be well-known, and the intakes should also be capable of delivering the requested flow.
The water guard has a crucial role and he must be a man trusted and respected by the farmers. It is preferable that he lives among the farmers of the canal in order to facilitate communications, and he must be able to undertake elemental calculations to adjust demand and supply.
To avoid possible excess in water use by the farmers some restrictions may be imposed, such as: the number of irrigation per year is limited, or a certain time (7-10 days) must elapse between two requests for water, or those who in a given month have already received water have a lower priority than those who have not, etc.
Another advantage of this system is that when the need arises (peak month) or during exceptionally dry years, it can also function on a fixed rotation.
The only disadvantage of this distribution system is its low efficiency at times of low demand, because the opening and closing of canals for a few farmers could imply considerable losses. However, the problem is mitigated since at times of low demand water losses are not so relevant.
This system is adopted particularly where there is mixed control of management. The public administration undertakes the operation of the main and secondary canals, and the farmers either take the water freely from those canals or distribute it themselves from a smaller canal.
The main feature of this system is that canals receive water in turns. For instance, in Upper Egypt, all the canals of a given region are classified as either A or
b. All those classified A receive water for seven days, and are then closed for seven days, while the B canals receive water when the A are closed. These turns may be changed during the irrigation season and vary from region to region.
The duration of the turns is generally the result of experience in the area. When the number of crops grown in the irrigation project or region is fairly large, there is not much opportunity for rationalizing the duration of the turns. However, where the number of crops is limited or some crops clearly prevail, the duration of the turns can be determined in a rational way. Annex II gives an example of a generalized procedure for the determination of the minimum irrigation turns.
When it is their turn, the farmers take the water from canals on free demand or they may eventually establish some kind of rotation among themselves. In the first case, which is the more frequent, the canal must be designed to cope with a concentration of demand at any time.
This type of distribution can be handled easily by public organizations but it implies large operational losses. The low efficiency of the system is mainly due to the fact that demand and supply are disassociated: canals are filled every turn irrespective of the demand. Some adjustments can be made in the canal water levels according to the demand pattern but still operational water losses are bound to be high. The system can easily be improved by properly organizing the farmers along the watercourses and regulating the flows according to the requests received from the groups of farmers on each watercourse. Under this hypothesis the system could be much more effective.
In this system all canals receive water by turns and farmers on the tertiary canals or watercourses receive water at a pre-set time and in the allowed quantity. This system is an improvement on the previous one where the rotation is not only of the main canals receiving water but also of the farms. It is a highly efficient system from the operational point of view and socially fair since it gives an equal chance to everyone.
There are several ways in which a rotational system can be implemented:
i. The water is distributed by turns of equal duration throughout the irrigation season. The farmer receives the water on a fixed day for an amount of time that is always constant, regardless of the crops that he may plant.
ii. The water is distributed by turns of different duration, longer at the beginning and end of the irrigation season and shorter in the middle, according to crop demand. The order of distribution within each turn is always the same and the amount delivered is constant throughout the season.
iii. The water is distributed by turns of different durations and the amount delivered also changes throughout the season. The amount delivered is calculated according to the actual crop water requirements.
The degree of technicality increases from (i) to (iii) and this not only refers to the actual calculation of the amounts of water to be delivered but also to the design of the irrigation network. For instance, method (i) can only be applied if the irrigation network has water measuring devices for each farm.
Method (i) is the simplest of the three and perhaps the most widely used. Socially speaking, it is a fair method, since it gives every user an amount of water proportional to the amount of land. If water is extremely scarce, the method is still quite efficient as the farmer must adapt his cropping pattern to the fixed turns. Calculations for the water delivery are simple and can be made easily.
Method (ii) requires a little more technical knowledge as the intervals must be adapted more to the actual needs of the crops. This can be very effective when the scheme is concerned with monoculture but the more diversified the production, the less effective will it be.
Method (iii) technically offers the best opportunity to meet crop water requirements and achieve greater water efficiency. However, it is difficult to implement. First of all, water measuring devices are needed at the farm level in order to measure the amount of water that must be delivered. Secondly, the management must have an excellent communication system in order to inform the farmers well in advance about their turns. Thirdly, since the calculations for the amounts of water to be delivered are made by the management and change from one irrigation to the next, the system is very vulnerable to malpractice. Fourthly, the calculation procedures are quite complicated and lengthy, needing qualified staff for their execution. As a result of all these requirements, this method is rarely used, in spite of its theoretical advantages.
In most of the rice growing areas, paddy fields are submerged continuously throughout the crop growing period. In irrigated conditions this permanent submergence is normally achieved by providing a continuous feeble flow that compensates the crop's daily evapotranspiration and percolation. Any excess water is drained away from one field and provides the supply for the next lowlying field.
Continuous flow is perhaps the simplest water distribution system, but it is also the least efficient because delivery is generally from field to field, resulting in large evaporation losses. These are inevitable since the water moves from top to bottom in a thin, but extensive layer. Under this system water losses by deep infiltration and excessive runoff are high.
Where water is scarce, the continuous flow system can lead to considerable social unrest because farmers on higher land get the water needed while those lower down get very little or nothing.
Although continuous submergence of paddy fields has certain advantages (saving of labour, prevention of crop damage, better control of weeds, etc.), the system is more and more restricted to areas where water is plentiful and its efficient use is therefore less important.
In areas of water shortage, continuous flooding is gradually being replaced by "intermittent irrigation"1. With this system, any paddy field can be filled or drained at will by the farmer within the restrictions imposed by the irrigation and drainage network. Of course, it implies the existence of a complete and usually expensive system of irrigation and drainage with the necessary control structures. Water savings of 20-30 percent can be obtained by intermittent irrigation, when compared to continuous irrigation. This system also helps plant growth through periodic drainage and reduces any tendency for fertilizer to be leached.
1 The term "intermittent irrigation" means the intentionally controlled supply of water to paddy fields by the farmer.
This is an extremely important activity, with two main purposes: (i) short-term: acting as a means of management control - comparing the actual pattern of water distribution with what it should have been and helping to identify reasons for divergences; and (ii) long-term: amassing information on water supply, demand and performance etc. in past seasons as a guide to planning and implementation in forthcoming seasons.
In larger schemes, a full-time monitoring and planning unit should be attached to the Operation Service to undertake these functions, as indicated in Figure 11.
Besides the day-to-day activities in relation to water distribution, important functions that this unit could perform are: (a) the preparation of the annual Irrigation or Crop Plan; and (b) preparation of the Annual Report covering the irrigation season to account for the water distribution affairs throughout the season. It is essential that only relevant information (for the purposes of performance evaluation and future planning) should be included. A lot of Annual Reports are compiled for routine purposes only and are of very little value as management tools because the wrong information has been collected, or the information collected has not been correctly collated or analysed. It is also important that the accuracy of the data should be regularly checked; this means checks not only on equipment (e.g. measuring gauges) but also on the junior staff who do the recording.
A monitoring and planning unit could also be extremely useful in irrigation systems affected by drainage problems, in order to monitor the behaviour of the system. Irrigation systems affected by problems of periodic increases in sediment in the water or poor quality could also benefit greatly from the services of the monitoring and planning unit.
The establishment of agro-meteorological stations within the area of an irrigation scheme is most advisable in medium or large schemes to provide data for sound calculation of crop water requirements and water balance studies. The systematic collection of these data is essential for the proper operation of the system. Whether these data should be collected by the monitoring and planning unit, the irrigation scheme itself or the meteorological services is largely a question of internal agreement between these organizations, but in any case the data must be made available to the management of the irrigation scheme.
5.5.1 Water guards
5.5.2 Operators of large structures
5.5.3 Pump-set operators
5.5.4 Water masters
5.5.5 Chief of the operation service
5.5.6 Auxiliary staff
To function adequately an Operation Service requires the following personnel:
- Water guards
- Operators of large structures (main canal gates and intakes and dam gates)
- Pump-set operators
- Water masters
- Chief of Operation Service
- Auxiliary staff (drivers, clerical staff, secretaries).
The main responsibilities and manpower requirements for each of the above personnel are discussed below. With regard to the staffing, it should be noted that it can vary greatly depending on the technical characteristics of the irrigation system (number of control structures, complexity of information required about farmers' demands, etc.) and the social attributes of the farmers (educational level, size of holding, etc.). Staffing requirements are also obviously affected by the nature of local transport facilities and telecommunications.
Ditchriders, ditchtenders, water guards, guards, water bailiffs, "zanjeros", and some other local names are used to designate this key man in the operation of the irrigation scheme. They are the main communication channel between the scheme management and the farmer, so the success of a smooth relationship between the two parties depends on their capabilities and honesty. Their main characteristics are described below:
a. Job description: Although these may vary slightly according to the type of scheme, the usual tasks are:- distribute and control the flows that each intake must deliver
- open and close intake gates or valves
- collection of the water requests
- preparation of the daily forms for the water delivery
- communication to the master water guard of the request for water
- control of the canals and watercourses to avoid unauthorized use of water
- compilation of agricultural and water data as needed
- delivery of water bills.
In many irrigation schemes, the water guards not only perform functions related to the operation of the system but also maintenance work during the off-season. In such cases the added duties are:- cleaning of the irrigation canal and ditches
- small repairs in the small hydraulic works (intakes, siphons, joints, etc.)
- supervision of workers doing any needed major repairs
- repairing and maintaining gates.
b. Qualifications: Basic primary school education is normally sufficient to undertake these functions. Water guards should have neither relatives nor properties in the areas they serve. They should be people of recognized honesty. They should also have farming and irrigation experience.
c. Manpower requirements at scheme level: The number of water guards needed at the scheme level is greatly influenced by the type of water distribution used and by the number of intakes to be controlled. Table 1 gives some average standards derived from projects in several parts of the world. Local circumstances, such as ease of access, particular configuration of canal layouts, transport facilities, etc., may introduce considerable variations in the manpower requirements. As far as possible the water guard should be made responsible for entire ditches or watercourses, because there could be friction between people due to differences in criteria for the water distribution.
Table 1 WATER GUARDS REQUIREMENTS FOR EACH 5000 HA1
Type of water distribution
Size of the farm2
Large 5-10 ha
Medium 2-5 ha
Small 2 ha
Canal rotation-free demand
1 The figures quoted are averages of data gathered from several projects. Local circumstances, such as transport facilities, ease of access, particular configuration of canal layouts, etc., may reduce or increase the above standards. The figures refer to fully-developed projects.
2 It is assumed that each farm has one intake. When an intake serves several farms, it should be considered as a unit, made up of all the farms served by the intake.
NA = not applicable
The operation of main canals and large secondary canals requires a specialized operator to handle the flow regulating hydraulic structures. These operators have responsibility for the structures in a given stretch of canal. A main intake may require one or more operators depending on its complexity and hours of work.
Main canal operators are frequently given round-the-clock responsibility and should therefore live in proximity to the stretch for which they are responsible, housing being provided by the management. They are often connected by telephone or radio with the Head Water Master in the main office. Information from the water guards is passed to the main office, where it is computed and orders for the control of flows are passed back to the canal operators.
The same applies mutatis mutandis to the operator of dam sluices where the main use of the dam is for irrigation.
a. Job description:- read the water levels in the canal, river or reservoir
- transmit data to Head Water Master
- manipulate gates and structures as indicated by main office
- receive data from master guards as to the required amount of water, and transfer data to the main office
- report to the Head Water Master any malfunctioning of gates and structures
- control and report on the state of maintenance of the stretch of canal for which he is responsible.
b. Qualifications: Completed secondary school education can be sufficient. Some mechanical knowledge is desirable.
c. Manpower requirements at scheme level: Data from several projects indicate that one canal operator can cover 10-15 km depending on the number of hydraulic structures in the canal. The main intake needs one or two people depending on the complexity of its operation. One person is also sufficient for the operation of the dam gates.
Where pump-sets are used either for lifting groundwater or surface water, pump operators are needed. They are particularly liable to abuse their positions because they have monopoly control over distribution within the areas commanded by their pumps. To keep this situation in hand, effective management control systems are especially important, linked to incentives, e.g. through promotion, to induce correct operation.
a. Job description:
- start and stop engines and motors
- operate engines or motors under the most suitable conditions
- provide for the regular maintenance of pump and engines/motors
- check the well discharge regularly check the number of hours that the pump is utilized by each farmer or group of farmers (where applicable)
- ensure the requisite supplies of fuel oil and grease are available.
b. Qualifications: Those who complete secondary school education can be pump operators provided short training courses are given to them on the operation of pump-sets. It is desirable that pump operators be mechanics, or alternatively have mechanical training; however such people are usually in short supply. Where the pump operator is responsible for providing the water to the farmers, he must be a man of known integrity because undesirable situations can arise when an operator accepts bribes from farmers or is a party to other malpractices.
c. Manpower requirements: Normally there is an operator for each pump-set (in the case of wells) for each turn of 8-10 hours. Where several pump units are grouped together the whole group also needs one operator for each turn. Manpower requirements for pump operators can be reduced by automation of the operation.
Water masters, known also as "master water guards", "head water bailiffs", "water foremen" or "capataces riego", supervise the ditchriders and canal operators and are the main channel of communication with the Chief of the Operation Service. Such an appointment is only necessary when the group of water guards to be supervised is larger than 12-15, otherwise the Chief of the Operation Service can do the supervision himself.
a. Job description:- receive the water request from the water guards transmit the water request to the Chief of the Operation Service
- coordinate, with the canal operators, the operation of the main canal gates
- transmit operational orders to the water guards according to instructions received from the Chief of the Operation Service
- supervise that the orders transmitted to the water guards are executed accurately.
Where the Operation Service is entrusted with maintenance responsibilities during the off-season, the water master supervises major and minor maintenance work.
b. Qualifications: Secondary school level. Ability to manage and direct people. Preferably he should have a number of years of experience on the same scheme.
c. Manpower requirements: The number of watermasters is dictated by the management rule that direct supervision can only be exercised over a limited number of people (5-10), although there are exceptions depending on the complexity of the coordinating and supervisory tasks, as well as on the nature of communications, transport, etc. In line with this rule, experience has shown that for most of the existing irrigation schemes, the standard is one water master for each 6-12 water guards.
The other determinant element is that the water master should, as far as possible, be responsible for one or several hydraulically independent sections, i.e. those served by a single canal.
The Chief of the Operation Service - also called Irrigation Supervisor - is responsible for the operation of the whole scheme or a large section of it. His main function is to collect the information provided by the water guards, process it, and issue the operational orders to be executed.
a. Job description:- responsible for the preparation of the annual irrigation plan
- contribute as required to the preparation of the annual report
- schedule the operation as planned
- supervise all the aspects related to the operation of the scheme
- impose fines and penalties on farmers breaking the rules as adopted in the rules or regulations of the scheme
- control operational expenses
- ensure the supply of materials necessary for continued operation.
Where the operation and maintenance activities are carried out by the same unit, the responsibilities of the Head Maintenance Engineer may have to be added.
b. Qualifications: The incumbent should be a qualified irrigation engineer (MSc), i.e. someone with a technical understanding of soil-water-plant relationships as well as engineering matters (hydraulics, construction, etc.). He should have at least five years of professional experience in the field. An agricultural engineer could also qualify, provided that proper experience in operational matters has been gained.
Fig. 11 Typical organization of an Operation Service
The ability to direct and coordinate people is an essential requirement.
c. Manpower requirements: A Chief of the Operation Service is needed for medium or large irrigation schemes (2000 to 50000 ha). For larger independent sections of 30 to 40000 ha, each with its own Head of Section, overall supervision is necessary by the Chief of the Operation Service. In the latter case, the qualifications of the Chief must be appropriately upgraded.
On the contrary, in small irrigation schemes (less than 2000 ha), the functions of the water master can be merged with those of the Chief of the Operation Service.
Auxiliary staff (drivers, bookkeepers, clerical staff, etc.) should be limited to the minimum indispensable to undertake the necessary work. When possible, these services should be provided by a pool serving the other units (maintenance, administration, etc.).
Little equipment is needed for the operational activities, although it does include items for transport. The following are usually needed:
a: for the Water Guards: portable water measuring devices can be used to check water flows when the irrigation system is not equipped with water measuring structures. Bicycles or motorcycles help to improve the service.
b: for the Canal Operators: radio or telephone for communicating with the main office. They should also have good transport facilities.
c: for the Pump Operators: adequate mechanical tools for their maintenance work. Transport of fuel, oil and grease should be arranged by the main office.
d: for the Main Office: small desk calculators and desk computers are necessary for medium-scale schemes. The value of using desk computers or larger ones depends on the complexity of the water distribution methods being used, but they are becoming increasingly popular in several countries (USA, France, Spain, Mexico and others).
The hierarchical basis for the organization of the Operation Service was given in Chapters 2 and 4. The example given in Figure 11 illustrates a typical organization of an Operation Service. As mentioned earlier, the establishment of a Planning and Monitoring Unit to assist the Chief of the Operation Service is highly desirable, particularly in large and medium schemes.