Practices of Irrigation & On-farm Water Management: Volume 2

The conveyance efficiency in irrigation projects is poor due to seepage, percolation, cracking, and damaging of the earth channel. Seepage loss in irrigation water conveyance system is very significant, as it forms the major portion of the water loss in the irrigation system. Irrigation conveyance losses controlled through lining may reduce the drainage requirement and also enhance irrigation efficiency. As such, reliable estimates of quantities and extent of seepage losses from canals under pre- and post-lining conditions become important. Various methods are used to estimate the canal seepage rate. The loss in conveyance is unavoidable unless the canal is lined. Lining may be done with a large variety of materials. Selection of a suitable one depends mainly on cost, performance, durability, and availability of lining materials.

The application of water to soils for crop use is referred to as irrigation. Irrigation systems differ greatly depending on what they are going to be used for. They range from the simple hand watering method used in most home gardens and many nurseries to the huge flood and furrow irrigation systems found in large-scale production. Surface (gravity-driven surface irrigation), sprinkler, drip/micro, and subsurface are types of irrigation methods that are used by growers to irrigate various crops. Each system has its advantages and disadvantages. But with good design, they can be very successful for appropriate cases. Water losses from irrigation vary with the type of irrigation method. The water management decisions strongly influence how uniform water can be applied through different irrigation methods to provide optimal soil water conditions for crop growth and marketable yields. The most appropriate irrigation method for an area depends upon physical site conditions, the crops being grown, amount of water available, and management skill. This chapter gives some very broad guidance and indicates several important criteria in the selection of a suitable irrigation method.

Irrigation scheduling is the decision process related to “when” to irrigate and “how much” water to apply to a crop. The irrigation method concerns “how” that desired water depth is applied to the field. To achieve high performance in an irrigation system, it must be designed to irrigate uniformly, with the ability to apply the right depth at the right time. Properly designed, installed, maintained and managed irrigation systems greatly reduce the volume of irrigation water and hence save energy and money. Besides, it improves the crop yield and quality. This chapter discusses the detailed design aspects of different types of irrigation system. The design procedures are explained through sample examples.

Any water applied above that needed to grow a crop is inefficient use of water. In order to determine how much irrigation water to apply, it is needed to estimate irrigation efficiency. There are many definitions of irrigation efficiency. Which one to use depends on which aspect one is interested in. Efficiency can be measured at the scale of a whole catchment, at the individual plant scale, and at almost any level in between. The scale of measurement depends on the focus of the person doing the measurement. A range of issues affect irrigation efficiency.

Together with energy, water is one of the major fuels of economic development. A development plan, especially in a water-short area, such as an arid zone belt, or a flat area underlain by hard rocks without major surface streams, cannot be drawn unless a clear idea of water availability and costs has been reached.

A watershed is the geographic area where all water running off the land drains to a common outlet. Watershed management activities can be considered at the state, river basin, individual watershed level or regional scale. For improving watershed protection and restoration, it is a prerequisite to know how agricultural systems influence soil and water resources.

Chemicals from agricultural field and other sources frequently enter the soil, subsoil, and aquifer. This may happen either by normal management practices or by accident, and the resulting chemical residues pose hazards to the environment and ecosystem. Whether we are using fertilizer or other pollutants, it is useful to know how fast it moves.

Salinity is an important land degradation problem. Salinity is more widely known and refers to the amount of soluble salt in a soil. Sodicity refers to the amount of sodium in soils. The consequences of salinity have detrimental effects on plant growth and final yield damage, reduction of water quality for users, sedimentation problems, and soil erosion. When crops are too strongly affected by the amounts of salts, they disrupt the uptake of water into roots and interfere with the uptake of competitive nutrients.

For the maximum growth of plants, it is essential to provide a root environment that is suitable for it. Water logging has an effect on the uptake of nutrients by plants. Drainage provides favorable condition for root growth, enhance organic matter decomposition, reduce salinity level above the drain, and maintain productivity of the land. For successful drainage design, the complex interaction of water, soil and crop in relation to quality of water must be well understood beforehand. The knowledge of drain material (drainage conveyance conduit) and placement technique of the drain (including selection of envelop material and its design with respect to soil bedding) are also of great importance. Judgment of alternate design options, and, monitoring and evaluation of the system after installation are demanded for successful outcome from the drainage projects. Disposal and treatment issues of drainage effluent are of concerns now-a-days. This chapter discusses all of the above points.

In some cases, we need to know the knowledge of specific process within a complex system of interacting and interdependent phenomena, and then need to reintegrate such knowledge to obtain a comprehensive and accurate solution of the phenomena. Model is ideal to integrate the complex system and to obtain the answer if the condition is. It is merely a useful tool in obtaining answers in the choice of a decision or policy.

In most part of the world, water resources are finite and most of the economically viable development has already been implemented. In addition, population growth and the effects of cyclic droughts on irrigated agriculture have put pressure on the available water resources. Such prevailing conditions have the effect of creating an imbalance between the increasing water demand and limited available water supply. Under this perspective, effective planning and management can only be obtained on the basis of reliable information on spatial and temporal patterns of farmer’s water demand, on farming irrigation practices, and on physical and operational features of large-scale irrigation systems. The timely and reliable assessment and monitoring of water resources and systematic exploration and developing new ones is of paramount importance. For this, it is necessary to employ modern methods of surveying, investigations, design, and implementation. Remote sensing and GIS are viewed as an efficient tool for irrigation water management.

Every day, millions of water pumps deliver water from wells to homes, farms, and businesses. A pump is the link to the water resource. Without pumps, we could not access ground water. As energy costs continue to increase, developing more efficient equipment will contribute to saving energy. Significant opportunities exist to reduce pumping system energy consumption through smart design, retrofitting, and operating practices. Cost of water supply depends on the appropriate selection (type and size for the prevailing condition) and efficiency of the pumping equipments. Each type of pump has its merits and demerits. Proper selection of pumps, motors, and controls to meet the requirement is essential to ensure that a pumping system operates effectively, reliably, and efficiently. The basics of pump control systems and hydraulic system are useful in pump operation. A proper discussion of pumping considers not just the pump, but the entire pumping “system” and how the system components interact. The recommended systems approach to evaluation and analysis includes both the supply and demand sides of the system.

The growing energy use all over the world and the increase in energy cost result in an increase in the prices of energy-dependent products, such as crops, meats, etc. Environmental pollution caused by the use of traditional energy sources, such as fossil fuel, makes it necessary to find new solutions for this problem. In addition, sources of fossil fuel are being rapidly depleted and energy consumption is increasing at an exponential rate. Under such situation, renewable energies seem to be the alternative. Renewable energy effectively uses natural resources such as sunlight, wind, rain, tides, and geothermal heat, which may be naturally replenished. Using renewable energy resources to power an irrigation system is a means of decreasing the dependency of food products on the prices of fuel and minimizes the impact of the irrigation system on the environment.