Contents preface (VII) introduction 1—37

1.9.3. Planning of an Irrigation Project
Once the project is considered feasible, the process of planning starts. Sufficient planning of all aspects (organisational, 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:
(i) Preliminary planning, and (ii) 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:

(i) Type of project and general plan of irrigation works,

INTRODUCTION

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(ii) Location, extent and type of irrigable lands,

(iii) Irrigation requirements for profitable crop production, (iv) Available water supplies for the project,

(v) Irrigable (culturable) areas which can be economically supplied with water, (vi) Types and locations of necessary engineering works,

(vii) Needs for immediate and future drainage, (viii) Feasibility of hydroelectric power development,

(ix) Cost of storage, irrigation, power, and drainage features, (x) Evaluation of probable power, income, and indirect benefits, (xi) Method of financing the project construction,

(xii) Desirable type of construction and development, (xiii) Probable annual cost of water to the farmers,

(xiv) Cost of land preparations and farm distribution systems, and

(xv) 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 analysing all available data for 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 (surface 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. There can be different

20 IRRIGATION AND WATER RESOURCES ENGINEERING
types of possible feasible plans for a particular project. Advantages and disadvantages of all such possible alternatives must be looked into before arriving at the final plan for the project.
Possibilities of using irrigation structures (dams and canal falls) for the development of hydroelectric power should also be examined in project planning.