The role of irrigation in increasing agricultural production is well recognized and as a result several irrigation systems have been established all over the world. In all most all the countries in the Asian region considerable number of irrigation systems have been constructed.
However, the performance of these irrigation systems has come in for considerable criticism. Among the irrigation systems, the relatively larger ones have been subjected to more criticism while the smaller ones appear to have performed well.
In case of the large irrigation systems, several adverse performance parameters have been mentioned. These include economic factors like inadequate returns on investments, performance factors like low water use efficiencies, social factors like failing to achieve equitable water distribution and finally environmental factors like soil salanization, contamination of groundwater resources and adverse public health effects.
In this article some aspects of irrigation systems management are outlined. These management steps will improve the operation of the system and also help in environmental protection.
Irrigation Systems Management:
A large irrigation system usually consists of one or more storage reservoirs or diversion structures (or pumping plants) and delivers water to the command area through a network of canals and related structures. Water is delivered to several farmers with individual land holdings.
The irrigation systems, by and large are operated by State officials who have to ensure the water supplies to the farmers. The crop production in the area and in turn the farmers’ incomes depend heavily on the irrigation supplies.
The irrigation systems should therefore be considered as economic enterprises and operated with management focus. After an irrigation system is constructed and comes into operation, the existing cropping patterns undergo a change.
The available water supplies in an irrigation system are not the same every year and the structures constructed could deteriorate with time. In addition, because of the large volumes of water delivered to the command areas, the environmental conditions in the command areas undergo certain changes.
The system operation should be planned in such a way that the available supplies are equitably distributed, the delivery systems are properly maintained and finally the environmental hazards are kept to a minimum.
The system should have plans for the years when water supplies available are below normal or for years when the system may have to withstand excess water in the form of floods.
The following items that constitute an irrigation system management are outlined:
1. Reservoir Operating Rules in Multipurpose Projects:
The sources of irrigation water for some irrigation systems are multipurpose reservoirs constructed for flood control, hydropower generation and water supply. The impounding dam is generally located in the upstream portion of the basin and releases water through spillways and through turbines for power generation.
The water is picked up downstream through weirs and barrages and diverted to the irrigation system. The operation of a multipurpose reservoir is to be coordinated according to the requirements of the power generation system, downstream demands and flood control aspects.
In order to cater to the demands, such projects normally setup operating rules for the reservoir operation. The use of water from the reservoir has to be planned in advance in order to specify the likely water allocation for each of the demand.
In such projects, in times of water shortages, the hydropower generation component is generally not compromised and the irrigation supplies could be curtailed. The reservoir operating rules need to be understood and irrigation demands are to be managed along with other demands.
The most important aspect of an irrigation system management is the delivery of water from the storage or diversion to the farmers’ fields. In case of smaller systems, water might be conveyed through a single channel and directly delivered to the fields.
In case of the larger systems, water is conveyed through a network of main and secondary canals with several controls and finally delivered to the tertiary units. It is very difficult to have a uniform policy of water allocation and deliveries in case of large systems.
The two main issues with the water deliveries are the rate of flow and the duration for which the water is provided. Beyond the project outlet, the delivered water is distributed to the farmers’ fields containing usually more than one crop.
In an ideal situation the total water deliveries should match with the crop requirements. The mismatch between deliveries and requirements (Fig. 19.2) will result either in excess or deficit supply. In a given situation, it is desirable to keep either the excesses or the deficits to a minimum.
Most of the irrigation systems maintain agro-meteorological observatories and the data from these stations should be utilised both for estimating the crop water requirements and planning water deliveries. In rainy season, particularly in case of lowland paddy, water deliveries could be adjusted with rainfall.
Water deliveries for salt affected areas in an irrigation system need to be carefully monitored. There will generally be more and more demand for water in such areas, but increased water deliveries should not aggravate the waterlogging problems.
In terms of the water deliveries, the following points need to be attended to in each irrigation system:
i. Assess the water requirements and adequacy of water deliveries at various levels (e.g.,. tertiary and secondary), from the perspectives of both the water suppliers and water users.
ii. Identify the underlying principles and procedures for decisions on the timing and amounts of water allocated at various levels within an irrigation system, both before the irrigation season begins and during the season when unexpected water shortages may occur.
iii. Evolve policies of water deliveries at different levels and make aware of the policies to the operating officials as well as the farmers.
The success of an irrigation system depends on the attention given to on-farm development and water management. When some of the large irrigation systems were planned and constructed, it was thought that once the water is delivered to the farmer, the objectives will be achieved.
Experience has shown that the farmer needs considerable assistance in bringing his fields to suit irrigated agriculture. In smaller systems, on-farm development could be taken up on individual holdings basis but in larger systems, it has to be undertaken on the basis of tertiary units.
For on-farm development the following could be considered:
1. Consolidation of land holdings wherever possible and applicable.
2. Land grading and field layout for surface drainage.
3. Lining of field water courses along with ancillary structures.
4. Surface irrigation design.
5. Irrigation schedules.
On-farm development has to be closely followed by the introduction of improved agricultural practices like adoption of improved crop varieties, use of fertilizers, crop pest control etc. In many irrigation systems, on-farm development work is not with the agency responsible for the main system construction and operation.
Again, the agricultural extension activities are not a part of the irrigation system operation but handled by a different organization. The administrative boundaries of the agency responsible for the agricultural extension activities may not coincide with the boundaries of the irrigation system command causing administrative difficulties.
4. Environmental Hazards:
The occurrence of several environmental hazards in major irrigation systems is a cause of considerable concern at present. Introduction of irrigation is bringing certain favourable and unfavourable changes in the command areas of irrigation projects.
Primarily there is a change in the cropping patterns due to the availability of water for agriculture. Changes in groundwater levels and in many cases change in the quality of groundwater in the command areas have been reported.
The need for constructing drainage channels have been felt in all the large scale irrigation projects. Drainage waters in many cases are of poor quality and the drainage channels become source of aquatic weeds. Because of a rise in groundwater levels, waterlogging and salinity problems appeared in several projects.
One major aspect which has not received adequate attention is the effects on health of the habitants in the command area. Many of the changes in the environmental factors have created conditions hazardous to human health.
Two groups of water-related diseases, the water-based and water-related vector-borne diseases, are most likely to be found in areas where irrigation has introduced large new water surface areas like lowland paddy. The diseases include malaria, schistosomiasis, lymphatic filariasis, onchocerciasis (river blindness), Japanese encephalitis and some other viral diseases transmitted by insects.
The settlement of new residents may bring in people without immunity, or they may bring new sources of infection or in more dense settlements disease transmission may be facilitated. Oomen et al. (1991) examine the irrigation-health problems in detail and offer suggestions for reducing health hazards.
The environmental hazards that are likely to occur in an irrigation system could be listed as follows:
1. Soil degradation, salinity and alkalinity.
2. Deterioration of groundwater quality.
3. Deterioration of surface water quality.
4. Waterlogging, formation of stagnant water pools and vector breeding places.
5. Stagnant drainage channels with aquatic weeds.
6. Changes in cropping patterns resulting in cropping systems injurious to human health.
7. Uptake of undesirable elements by plants causing long term health problems.
8. Spread of certain water borne diseases.
9. Irrigation return flows causing water quality problems for aquatic habitat.
10. Contamination of irrigation water with urban wastes.
5. Water Users’ Associations:
Farmers participation is not only useful but at times becomes essential for an effective management of the irrigation system. The assistance of the water users association could be taken in distribution of water in the tertiary units, settling minor disputes in water allocation and if possible in the maintenance of the system at the tertiary level.
In respect of the water users associations the following items need to be considered:
1. Type of water users association, formal or informal organization.
2. Methodology for introducing and strengthening the association.
3. Structuring of the association according to its functionality, according to village structure and hydrological unit.
4. Arrangements for membership and leadership.
5. Support for water users’ association from government agencies and others.
6. Activities undertaken by the water users’ association in irrigation management.
7. Financial structure of the water users’ association, membership fees and O&M costs, government subsidies.
8. Participation of water users’ association in the planning, design and construction of irrigation improvement works.
9. Capabilities in managing its resources, in keeping its records and in setting and implementing rules and regulations.
10. Conditions and factors affecting farmers’ participation relating to physical factors and in particular to socio-economic factors.
The management of the watershed area which supplies water to the irrigation reservoir may not be strictly come under irrigation system management. However, the erosion process in the catchment could bring in considerable quantities of sediment which affect the reservoir. In case of some reservoirs intensive conservation measures could reduce the inflows into the reservoir. All these factors need to be taken into consideration.
In spite of the general awareness of the requirement of drainage in irrigation systems, the implementation of the drainage measures has not progressed to the desired extent. The problems of salanisation and raising groundwater levels are being reported in some irrigation systems. As an initial step, in all irrigation systems, surface drainage systems should be given attention and these should be installed as per requirement.
Large scale subsurface drainage systems have not been installed in the Asian region except in the Indus basin in Pakistan. Some efforts relating to the installation of tile drain systems are reported from India.
It is reported that subsurface drainage systems are installed in considerable areas in Japan. The concept of subsurface drainage appears to require further investigation for large scale adoption in the irrigation systems in the Asian region.
8. Infrastructural Development:
Irrigation systems as they come into operation, change the cropping patterns and contribute to increase production of several agricultural commodities. The farmers in the irrigation command areas should be assisted by way of providing marketing facilities, roads etc. Quite often these activities do not fall under the purview of the irrigation system manager, but he has to negotiate with other organizations to get such activities initiated.
The project should also have good communication facilities for operating the water delivery system and for emergency maintenance operations.
9. Water Pricing and Irrigation Service Fee:
There appears to be no uniform policy regarding the charges for irrigation supplies effected through the irrigation systems. In some large systems, no charges are levied (as in Thailand) while in many of the systems nominal charges are imposed on the farmers based upon the extent of the irrigated area.
The water pricing in irrigation systems is an issue for consideration. Suitable charges levied from the beneficiaries could meet the maintenance cost of the system and may also contribute to the farmers’ awareness and participation in the water management aspects in the irrigation systems.
10. Diversified Use of Irrigation Systems:
Even though irrigation systems are designed essentially for providing water for crop production, in some instances irrigation water is being used for other purposes like municipal and industrial uses.
Such uses need not necessarily be banned but should be taken to ensure quality standards. Also municipal or industrial activities should not result in the contamination of water in the irrigation system.
The irrigation system manager should be aware of the diversified uses of the system. Crop diversification and possibilities for aquaculture need to be investigated wherever possible.
Monitoring and Evaluation of Irrigation System:
Each irrigation system should have a regular program of monitoring and evaluation. The monitoring and evaluation programs should be separated from the normal water delivery and maintenance operations.
Monitoring should consist of both physical and economic parameters and should include the following:
1. Climatic parameters at selected locations in the command area.
2. Cropped areas.
3. Water deliveries.
4. Groundwater levels.
5. Drainage conditions.
6. Condition of the water delivery system.
Evaluation of the irrigation system should consist of a set of performance indicators.
These may include the following:
1. Area of land irrigated in relation to water supply.
2. Crop yields in the command area.
3. Profitability-actual income for the farmer.
4. Volume of complaints against the agency.
5. Illegal tapoffs in the system and other administrative problems.
6. Departure from planned cropping pattern.
7. Comparison between canal head and tail performance.
8. Responsiveness of agency to farmers’ needs.
It is difficult to develop a uniform procedure for evaluation of all irrigation systems as the physical conditions under which each of the systems operate are different. An attempt should therefore be made to define or develop a set of performance parameters for a particular irrigation system and evaluate these parameters either seasonally or annually.
Molden and Gates (1990) and Rao (1993) present a set of parameters for evaluating irrigation water delivery systems. These parameters consist of adequacy, efficiency, dependability and equity of the water delivery system.
The major state variables that determine water delivery system performance refer to either volume, rate, frequency or duration of water delivery.
At a point x in the system and at time t, these state variables can be defined as follows:
QD (x, t) – Actual amount delivered by the system.
QR (x, t) – Amount of water required for consumptive and other uses downstream of the delivery point x.
CVT – Temporal coefficient of variation (ratio of standard deviation to mean) over the time period T.
CVR – Spatial coefficient of variation over the region R.
Using these values, Molden and Gates (1990) define the different measures of performance as follows:
The above parameters can be estimated either at the tertiary unit level or higher aggregation levels. Extensive measurements of QR and proper estimate of QD values are needed. Procedures for numerically calculating these parameters have been indicated.
This is one example and there could be other ways for evaluating the water deliveries and the overall performance of the system. With the available procedures and information, each system should have some procedure for its evaluation, the results of which could be useful for improving the system performance.