Chapter: Civil - Water Resources and Irrigation Engineering - Irrigation Engineering

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Planning of Irrigation Projects

Agricultural establishments capable of applying controlled amounts of water to lands to produce crops are termed irrigation projects.

PLANNING OF IRRIGATION PROJECTS

 

 

Agricultural establishments capable of applying controlled amounts of water to lands to produce crops are termed irrigation projects. These projects mainly consist of engineering (or hydraulic) structures which collect, convey, and deliver water to areas on which crops are grown. Irrigation projects may range from a small farm unit to those serving extensive areas of millions of hectares. A small irrigation project may consist of a low diversion weir or an inexpensive pumping plant along with small ditches(channels)and some minor control structures .A large irrigation project includes a large storage reservoir , a huge dam ,hundreds f kilometers of canals, branches and distributaries ,control structures ,and other works. Assuming all other factors (such a enlightened and experienced farmers, availability of goods seeds, etc.) reasonably favorable, the following can be listed as conditions essential for the success of any irrigation project.

 

 

(i)       Suitability of land (with respect to its soil, topography and drainage features) for continued agricultural production,

 

(ii)     Favorable climatic conditions for proper growth and yield of the crops,

 

(iii)  Adequate and economic supply of suitable quality of water, and

 

(iv)  Good site conditions for the safe construction and uninterrupted operations of the engineering works.

 

 

During the last four decades, many large irrigation projects have been built as multipurpose projects. Such projects serve more than one purpose of irrigation or power generation. In India, such large projects (singlepurpose or multi purpose) are constructed and administered by governmental agencies only .Most of the irrigation projects divert stream flow into a canal system which carries water to the cropland by gravity and, hence are called gravity projects. In pumping projects, water is obtained by obtained by pumping but delivered through a gravity system.

 

A gravity type irrigation project mainly includes the following works:

 

·     Storage (or intake) and diversion works,

·     Conveyance and distribution channels,

·     Conveyance, control, and other hydraulic structures,

·     Farm distribution, and

·     Drainage works.

 

Development of Irrigation Project:

 

 

A small irrigation project can be developed in a relatively short time. Farmers having land suitable for agriculture and a source of adequate water supply can plane their own irrigation system, secure necessary finance from banks or other agencies, and get the engineering works constructed without any delay. On the other hand, development of a large irrigation project is more complicated and time 'consuming. Complexity and the time required for completion of a large project increase with the size of the project. This is due to the organizational, legal, financial administrative, environmental, and engineering problems all of which must be given detailed consideration prior to the construction of the irrigation works. The principal stage of a large irrigation project are: (i) the promotional stage, (ii) the planning stage, (iii) the construction stage, and (iv) the settlement stage. The planning stage itself consists of three substages: (i) preliminary planning including feasibility studies, (ii) detailed planning of water and land use, and (iii) the design of irrigation structures and canals. Engineering activities are needed during all stages (including operation and maintenance) of development of an irrigation project. However, the planning and construction stages require most intensive engineering activities. A large irrigation project may take 10 '30 years for completion depending upon the size of the project.

 

Feasibility of an irrigation project:

 

 

A proposed irrigation project is considered feasible only when the total estimated benefits of the project exceed its total estimated costn project is feasible only if his annual returns (after completion of the project) exceed him annual costs by sufficient amount. The feasibility of an irrigation project is determined on the basis of preliminary estimates of area of land suitable for irrigation, water requirements, available water supplies, productivity of irrigated land, and required engineering works.

 

 

Planning of an irrigation project:

 

 

Once the project is considered feasible, the process of planning starts. Sufficient planning of all aspects (organizational, technical, agricultural, legal, environmental, and financial) is essential in all irrigation projects. The process of planning of an irrigation project can be divided into the following two stages:

 

1.     Preliminary planning, and

2.     Detailed planning.

 

 

Preliminary plans, based on available information, are generally approximate but set the course for detailed planning. Based on preliminary planning, the detailed measurements are taken and the detailed plans are prepared. Obviously, detailed plans are more accurate. Alterations in the detailed plans may be necessary at all stages of the project. The preparation of plans of an irrigation project in an undeveloped region is a complicated task and needs the expertise of specialists in areas of engineering, agriculture, soil science, and geology. The following are the main factors which must be determined accurately during the planning stage of an irrigation project.

 

1.     Type of project and general plan of irrigation works.

2.     Location, extent and type of irrigable lands,

3.     Irrigation requirements for profitable crop production

4.     Available water supplies for the project,

5.     Irrigable (culturable) areas which can be economically supplied with water,

 

6.     Types and locations of necessary engineering works,

7.     Needs for immediate and future drainage.

8.     Feasibility of hydroelectric power development,

9.     Cost of storage, irrigation, power and drainage features,

10.                        Evaluation of probable power, income and indirect benefits.

11.                        Method of financing the project construction.

12.                        Desirable type of construction and development.

13.                        Probable annual cost of water to the farmers.

14.                        Cost of land preparations and farm distribution systems, and

 

15.                        Feasible crops, costs of crop production, and probable crop returns.

 

 

Most of these elements of project planning are interrelated to some extent. Hence, the studies of the factors listed above should be carried out concurrently so that necessary adjustments can be made promptly as planning progresses.

 

 

The preliminary planning of an irrigation project consists of collecting and analyzing all available data fro the current study, securing additional data needed for preparing preliminary plans for major project features by limited field surveys, and determining the feasibility of the proposed development by making the preliminary study of major features in sufficient detail. While investigations for the preliminary planning of irrigation projects should be conducted with minimum expenditure, the results of the preliminary study must be sufficiently accurate. For preliminary investigations, hydrological studies can be based on the records of stations in the vicinity of the proposed project site. Suitability of land for cultivation purposes can be examined at representative sample areas. Foundation conditions at major irrigation works can be determined from surface and a few subsurface explorations. For detailed planning, accurate data on all aspects of the proposed irrigation project are required to work out the detailed plans and designs of various engineering works and to determine their economic site locations. Physical data needed for detailed planning are collected by topographic and location surveys, land and soil investigations and geological explorations (surfaces as well as subsurface) at the sites of major engineering works. Results of such surveys are suitably tabulated or plotted for convenient use in design offices and for planning further field work, if necessary. Hydrological data are usually determined by extensive studies of all available records and collecting additional data, if possible. Photographic records of pre 'construction (and also during construction) condition at locations of all engineering works and aerial surveys for dams and reservoir sites must be supplemented by accurate ground surveys. Geological explorations are also needed at the sites of dams, reservoirs, and major structures. Such data are useful in studies of water loss due to leakage and foundation designs. Sources of suitable amounts of building material (such as earth material, concrete aggregates, etc.,) must be located and explored. In case of insufficient supplies at the site, additional sources must be located.

 

Having collected the required data for detailed planning general plans for irrigation structures are prepared. Such plans are dependent on topography, locations of irrigable areas, available water sources, storage requirements and construction costs.

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