SCOPE OF IRRIGATION ENGINEERING
Irrigation engincering, as practised in ndia, is not confined only to the application of water to the land for raising crops.
It includes all aspects and problems extending from the watershed to the agricultural fields.
It deals with hydrology, river engineering, the design and construction of dams, weirs, canals and various other hydraulic and irrigation structures.
It also deals with the problems of sub-surface drainage, soil reclamation, irrigation practices and water-soil-crop relationships.
Generally, allied subjects such as flood control, hydropower, inland navigation are also studied in irrigation engineering.
In fact, irrigation engineering embraces almost all the aspects of water resources engineering and the multipurpose river valley projects discussed in the preceding section.
The various aspects of irrigation engineering can be divided into the following sub-heads :
1) WATER RESOURCES AND HYDROLOGY ASPECT :
The first aspect of irrigation engineering is to locate various water resources and to study the hydrology of the region.
The basic knowledge of water resources engineering and hydrology is essential for an irrigation engineer.
Hydrology is a science that deals with the depletion and replenishment of the water resources on the earth.
It includes study of meteorology, precipitation, stream flow, floods, river engineering, reservoirs and flood control.
While designing and planning various irrigation structures, such as dams, reservoirs, spillways. aqueducts and tube wells, the irrigation engineer requires the following information :
- The quantity of water that will be available at a reservoir site for storage. It is obtained from the actual stream gauging, and rainfall and runoff characteristics.
- The maximum discharge at a river site. Hydrographs and the flood frequency studies are made to estimate the maximum discharge.
- The reservoir capacity that would be required to assure adequate water for irrigation, hydropower, and municipal water supply.
- The quantity of ground water which can be economically exploited for various uses.
- The effects which are likely to occur on the discharge, water levels and characteristics of the river after the construction of various irrigation structures.
2) ENGINEERING ASPECT :
The engineering aspect of irrigation engineering involves development of a source of water for irrigation and construction of various irrigation structures for the storage, diversion, conveyance and application of water.
It is a vast field and can be subdivided into the following :
i) Dams and Water Power Engineering :
For utilisation of surface water, a dam is across the river to create a reservoir.
This phase includes the study of different types of dams, spillways, constructed dam outlets, hydroelectric power house, etc.
ii) Diversion and Distribution Engineering:
For perennial rivers, diversion head works are constructed to raise the water level and direct the water into the canals.
A pickup weir is required on a non-perennial river if there is a dam on the upstream which releases stored water into the river.
A distribution system consisting of a network of canals is required to convey the water to the agricultural fields.
This phase involves design and construction of the weir, head regulators, canals, falls, cross-drainage works, canal outlets and various other canal structures.
iii) Minor irrigation schemes :
This includes well irrigation, tank irrigation, bandhara irrigation and inundation irrigation.
3) AGRICULTURAL ASPECT :
The agricultural aspect involves irrigation practice and the study of agricultural characteristics of the land.
i) Irrigation Practice :
The water available at the canal outlet is taken to the agricultural fields through small channels called water courses.
Irrigation practice involves the estimation of the water requirements of the various crops.
It is also concerned with methods of application of water to the agricultural fields.
Design of surface and subsurface drains is important for the disposal of excess irrigation water to prevent waterlogging and salinity.
ii) Study of agricultural characteristics :
It includes the following :
- Proper levelling, shaping and preparation of the agricultural land before sowing.
- Soil investigations to assess the suitability of the land for various crops.
- Consolidation of the small and scattered holdings so that irrigation can be done economically for large fields.
- Design and construction of field channels which carry water from the water courses to the field.
- Selection of the proper cropping pattern to suit the soil, climate and other conditions.
- Assessment of the optimum water requirements of the crops and the proper depths of water cessary in a single application of water and the number of waterings.
- Methods for distribution of water uniformly and periodically to obtain the maximum crop yield.
- Determination of the water retention capacity of different soils and the permeability of the soils.
- Methods for reclamation of saline and alkaline lands to make them suitable for cultivation.
- Methods to control the waterlogging of the agricultural land.
- Methods for the protection of soils against erosion.
- Study and introduction of improved hybrid and high-yielding varieties of crops.
- Study of the ancillary inputs such as fertilizers, insecticides, pesticide, etc.
(iii) Command Area Development (CAD) :
An irrigation engineer should be well versed with the above mentioned agricultural aspects.
All those aspects are included in the general development of command area, popularly known as Command Area Development (CAD).
To take full advantage irrigation potential and to safeguard the interests of farmers, CAD is now considered as a necessary feature of all the major and medium irrigation projects.
4) MANAGEMENT ASPECT :
The management aspect is quite important for all irrigation projects. It deals with the successful implementation and efficient management of engineering an agricultural works discussed above.
Some of the points to be considered in the efficient management the project are as follows :
- There should be most economic use of available water so as to have the optimum benefits per unit of available water and also per unit of area land available.
- The cultivation should be carried out in the most scientific manner so as to obtain the maximum yield of crops.
- The distribution of water among various cultivators should be managed properly. Some kind of rotation system, such as warabandi, should be introduced.
- Reliable and efficient service should be provided to the cultivators so that the irrigation water is available to them as and when required.
- In order to increase the efficiency of irrigation, the small land holdings of the small farmers should be consolidated to form large holdings. If necessary, co-operative societies may be formed interest of small farmers.
- Proper arrangement for the measurement of water used by farmers and collection of water charges should be made.
- The ill effects of over-irrigation should be eliminated by adopting suitable measures.
- Various irrigation works should be properly protected and maintained.
- The farmers should be trained and educated to take full advantage of the irrigation water.
- Last, but not the least, the management must ensure protection of the environment and ecology Uncontrolled irrigation may result in water logging, salt problems, soil erosion and various other problems, leading to irreparable loss of precious soil mantle.